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Water scarcity assessments in the past, present and future

1 School of Environmental Science and Engineering, South University of Science and Technology of China, Shenzhen, 518055, China

2 Swiss Federal Institute for Aquatic Science and Technology (Eawag)

3 Department of Environmental Sciences, University of Basel, Switzerland

Simon N. Gosling

4 School of Geography, University of Nottingham, Nottingham, NG7 2RD, United Kingdom

Matti Kummu

5 Water and development research group, Aalto University, Finland

Martina Flörke

6 Center for Environmental Systems Research, University of Kassel, Kassel, Germany

Stephan Pfister

7 ETH Zurich, Institute of Environmental Engineering, 8093 Zurich, Switzerland

Naota Hanasaki

8 National Institute for Environmental Studies, Tsukuba, Japan

Yoshihide Wada

9 NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025, USA

10 Center for Climate Systems Research, Columbia University, 2880 Broadway, New York, NY 10025, USA

11 Department of Physical Geography, Faculty of Geosciences, Utrecht University, Heidelberglaan2, 3584 CS Utrecht, The Netherlands

Xinxin Zhang

12 School of Nature Conservation, Beijing Forestry University, Beijing, 10083, China

Chunmiao Zheng

Joseph alcamo.

13 Center for Environmental Systems Research, University of Kassel, Kassel, Germany

14 Institute of Industrial Science, The University of Tokyo, Tokyo, Japan

Water scarcity has become a major constraint to socio-economic development and a threat to livelihood in increasing parts of the world. Since the late 1980s, water scarcity research has attracted much political and public attention. We here review a variety of indicators that have been developed to capture different characteristics of water scarcity. Population, water availability and water use are the key elements of these indicators. Most of the progress made in the last few decades has been on the quantification of water availability and use by applying spatially explicit models. However, challenges remain on appropriate incorporation of green water (soil moisture), water quality, environmental flow requirements, globalization and virtual water trade in water scarcity assessment. Meanwhile, inter- and intra- annual variability of water availability and use also calls for assessing the temporal dimension of water scarcity. It requires concerted efforts of hydrologists, economists, social scientists, and environmental scientists to develop integrated approaches to capture the multi-faceted nature of water scarcity.

1. Introduction

Population growth, economic development and dietary shift (towards more animal products) have resulted in ever increasing water demand, and consequently pressures on water resources. Many parts of the world are enduring water scarcity which generally refers to the condition wherein demand for water by all sectors, including the environment, cannot be satisfied fully due to the impact of water use on supply or quality of water [ Falkenmark et al., 1989 ; Alcamo, et al., 2000 ; Vörösmarty et al., 2000 ]. In the Global Risks 2015 Report of the World Economic Forum, water supply crisis was identified as the top 1 high-impact risk for our current times [ World Economic Forum, 2015 ].

Understanding water scarcity is important for formulating policies at global, regional, national and local scales. “Addressing water scarcity and quality” is one of the six themes of the 8 th Phase of the International Hydrological Programme (IHP-VIII) that focuses on “Water Security: Responses to Local, Regional and Global Challenges (2014–2021)”. Similarly, it is a key focus of the scientific decade 2013–2022 of the International Association of Hydrological Sciences (IAHS), named “ Panta Rhei – Everything Flows”, which is dedicated to research activities on changes in hydrology and society [ Montanari et al., 2013 ]. A targeted working group on “Water Scarcity Assessment: methodology and application” was established in the Panta Rhei program to develop innovative methodology and conduct water scarcity assessment ( http://iahs.info/Commissions--W-Groups/Working-Groups/Panta-Rhei/Working-Groups.do ). “Substantially reduce the number of people suffering from water scarcity” is also one of the targets set in the Sustainable Development Goals recently adopted by the United Nations [ UN, 2015 ].

Since the late 1980s, when water scarcity became an issue, many indicators have been developed to facilitate the assessment of status of water scarcity across the world ( Table 1 ). Publications on water scarcity assessment have increased dramatically in the last two decades ( Fig. 1 ) amid the intensification of the problem in increasing parts of the worlds. Rather straightforward water scarcity indicators were developed in the late 1980s throughout the beginning of the 2000s, which were criticized for their focus on surface water and groundwater (so called blue water) only, neglecting the important role of green water (soil moisture fed by rainfall) and spatial and temporal variations [ Savenije, 2000 ; Rijsberman, 2006 ].

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The number of publications based on the keyword “water scarcity” from Scopus as of 17 January 2016. The years of publication of specific water scarcity indicators are marked.

Summary of the characteristics of water scarcity indicators. EFR stands for Environmental Flow Requirements.

Entering the 2000s, more sophisticated approaches with high spatial resolution have been developed, attempting to incorporate more aspects of water, such as: water quality, green water (soil moisture), and environmental flow requirements. In recent years, explicit representation of water quality and environmental flow requirement have been taken into account, through a multiple-value water scarcity indicator [ Zeng et al., 2013 ; Liu et al., 2016 ]. Although this development has increased understanding of the multi-faceted nature of water scarcity, these attempts usually focused on merely one aspect of water scarcity. In contrast to the wide use of the classical water scarcity indicators developed in the early years, the more integrated indicators have rarely been applied beyond the research groups where they were developed.

It is worth mentioning that most approaches for water scarcity assessment have used single indicators to quantify water scarcity. A few have combined two indicators. For example, Falkenmark [1997] assessed blue water scarcity with two indicators, water shortage and water stress (see Table 1 ), together using ‘Falkenmark matrix’. Kummu et al. [2016] used similar approach to Falkenmark [1997] for water scarcity assessment on the global level for the whole 20 th century. According to Kummu et al. [2016] , areas under both water shortage and stress have very limited adaptation options to alleviate the scarcity compared to areas under sole stress or shortage.

In this paper, we provide a comprehensive review of existing water scarcity indicators and reflect on their relevance in a rapidly changing world. Based on which, we highlight some major challenges faced in the future research and propose ways forward.

2. An overview of classical water scarcity indicators

2.1. the falkenmark indicator.

The Falkenmark Indicator [ Falkenmark et al., 1989 ], measuring water scarcity is a simple yet widely used method for calculating water scarcity. It requires: the number of people living within a given spatial domain and the volume of water (termed blue water by Falkenmark ) available within that domain. The volume of water available per person is then calculated in m 3 /cap/year. The indicator’s reliance on population leads to the Water Crowding Index (WCI), which measures the number of people per unit of available water, e.g., persons/million m 3 /year. A value of 1,700 m 3 /cap/year of renewable freshwater was proposed as the threshold for water scarcity [ Falkenmark et al., 1989 ], below which social stress and a high level of competition for water emerges [ Falkenmark and Rockström, 2004 ]. If water availability falls below 1,000 m 3 /cap/year then the area experiences high water scarcity , and below 500 m 3 /cap/year, absolute scarcity .

However, its ease of application is tempered by an important caveat: the index is only an indication of supply-side effects on global water scarcity [ Schewe et al., 2014 ]. The indicator overlooks temporal variability and the important drivers of demand, related to economic growth, lifestyle, and technological developments [ Savenije, 2000 ]. Management practices and infrastructure are not considered by the index and the simple threshold does not reflect the true spatial distribution of demand within and between the domains over which the index is calculated.

2.2. Water use to availability ratio

The water use to availability ratio, or criticality ratio, is another widely used indicator to assess water scarcity. The advantage of this ratio is that it measures the amount of water used, and relates it to the available renewable water resources [ Alcamo and Henrichs, 2002 ]. Over the past decades, the development of water use models has been fast, and water availability and use can now be modelled spatially explicitly on global scale with high spatial resolutions [ Alcamo et al., 2003a ; Hanasaki et al., 2008 ; Flörke et al., 2013 ; Wada et al., 2014 ].

Water use can refer to either water consumption or water withdrawals. Water consumption measures the amount that is removed from rivers, lakes or groundwater sources and evaporated to the atmosphere. Water withdrawal refers to the amount of water that is withdrawn from these sources, of which part returns to the system by leakage or return flows. The majority of the existing water scarcity studies use withdrawal to indicate water use [ Alcamo, et al., 2003b ; Oki and Kanae, 2006 ; Wada et al., 2011 ]. Recent work by Munia et al. [2016] uses consumption and withdrawals as a minimum and maximum levels of scarcity, respectively. However, since consumption is normally much smaller than withdrawal, the ratio of consumption to average available renewable water resources usually indicates an unrealistically low level of water scarcity.

Based on the water criticality ratio, high water stress occurs if water withdrawal exceeds 40% of the available water resources [ Alcamo and Henrichs, 2002 ]. However, as part of the withdrawal water returns back to water bodies and the actual proportion of the return flow vary across regions depending on natural and social-economic and technical conditions, using 40% as a water scarcity threshold may not be consistent in reflecting the status of water scarcity across regions.

2.3. Physical and economic water scarcity – the IWMI Indicator

The International Water Management Institute (IWMI) developed a more complex indicator for assessing water scarcity [ Seckler et al., 1998 ], combining the physical and economic water scarcities. Indicator takes into account the proportion of water supply, of a country in question, from renewable freshwater resource available for human requirements, while accounting for existing water infrastructure such as desalinization plants and water stored in reservoirs. A novel element of the index is that it considers an individual country’s potential to develop water infrastructure and to improve irrigational water use efficiency.

Their analysis yielded five country groupings. The country groupings were in turn used to define whether countries are either “physically water scarce” or “economically water scarce” [ Rijsberman, 2006 ]. The former is where countries are unable to meet estimated water demand in 2025, even after accounting for national adaptive capacity. The latter is where countries have a sufficient renewable water resource but would have to invest significantly in water infrastructure to make the resources available for consumption in 2025.

The index is available as a Microsoft Excel model [ Seckler et al., 1998 ] yet it has not been used as much as other indicators to assess global water scarcity, with exception to an assessment conducted by Cosgrove and Rijsberman [2000] . One reason for this is that it is considerably more complex than many other indices reviewed here and thus more time-consuming to compute. Another is perhaps that its interpretation is less intuitive than other indices and therefore less attractive for presentation to the public and/or a policy audience [ Rijsberman, 2006 ].

2.4. Water poverty index

The Water Poverty Index (WPI) proposes a relationship between the physical extent of water availability, its ease of abstraction, and the level of community welfare [ Sullivan, 2001 ]. It considers five factors: resources or water availability; access to water for human use; effectiveness of people’s ability to manage water; water use for different purposes; environmental integrity related to water and of ecosystem goods and services from aquatic habitats in the area. The WPI is mainly designed for assessing the situation facing poor water endowments and poor adaptive capacity.

The WPI is calculated with the weighted average of the five components, each of which is first standardized so that it falls in the range 0 to 100; thus the resulting WPI value is also between 0 and 100, representing the lowest and the highest level of water poverty [ Sullivan et al., 2006 ]. The indicator has the advantage of comprehensiveness. However, its application is hampered by its complexity and lack of information for some of the factors required for building the indicator on large scale [ Rijsberman, 2006 ]. It has so far only been applied at the community level for pilot sites in a few countries.

3. Progress in water scarcity assessment

Since the beginning of the 2000s, water scarcity assessment has entered an era characterized by the applications of more sophisticated models supported with spatial analytical tools. The water use to availability ratio has been the basis of many water scarcity assessment approaches developed during this period. The main efforts made in these assessments have been in the measurements of water “use” and “availability”.

3.1. Green-blue water scarcity

Green water refers to soil moisture in the unsaturated zone recharged by precipitation. It is a crucial water resource for agricultural production, responsible for about 90% of total water use of agriculture and 60% of the global food is produced without additional irrigation (i.e., blue water use) [ Rockström et al., 2009 ].

The development of the green-blue water indicator has attempted to incorporate green water in the assessment. The pioneer work was done by Rockström et al. [2009] who developed the first indicator to assess scarcity where both blue and green water resources are included. They measured the scarcity by comparing global average green-blue water consumption of 1300 m 3 /cap/year for a healthy diet (3000 kcal/cap/day of which 20% originates from animal sources) and locally available green-blue water resources. The area is under scarcity if available water resources are less than the average requirement of 1300 m 3 /cap/year. This was further developed by Gerten et al. [2011] who incorporated the local water requirements for a healthy diet to the calculations and thus taking into account spatial variations of the water needed to produce the actually grown food in different locations. These vary from less than 650 m 3 /cap/year in Europe and North America to over 2000 m 3 /cap/year in large parts of Africa [ Gerten et al., 2011 ; Kummu et al., 2014 ].

Despite the merit of incorporating green water in water scarcity assessment, the attempts so far suffer from a drawback of inconsistency. The blue water resources are generally quantified as the total run-off of renewable freshwater on the earth surface or given geographical locations/river basins, regardless of their accessibility. The green water resources, on the other hand, are quantified as the evapotranspiration of vegetation on croplands (and grazing land). This greatly underrepresents the quantity of green water resources because a large (if not larger) amount of evapotranspiration occurs on non-croplands.

3.2. Water footprint-based water scarcity assessment

The water footprint measures the amount of water used to produce the goods and services human uses [ Hoekstra et al., 2011 ]. Noting the problem of ignoring the return flow in using water withdrawal to refer to water use in the water scarcity assessment, Hoekstra et al. [2012] developed a water footprint-based assessment for global blue water scarcity assessment. Three alternatives are used in measuring water use and availability. First, water use refers to consumptive use of ground- and surface water flows – i.e., the blue water footprint. Second, the flows needed to sustain critical ecological functions are subtracted from water availability. A presumptive standard of 20% depletion rate is used as a threshold, beyond which, risks to ecological health and ecosystem services increase. Third, water use and availability are measured on a monthly rather than annual basis to account for seasonal water scarcity. The water scarcity indicator derived from this approach provides a picture of where and when current levels of water use are likely to cause water shortages and ecological harm within river basins around the world [ Hoekstra et al., 2012 ]. However, the assumption of EFR to be 80% of the total water resources across all the river basins in the assessment, as suggested by Richter et al. [2011] , is too simplistic, as it did not consider the complexity of EFR in individual river regimes. This may also overestimate EFR as well as water scarcity because the 80% EFR is set unrealistically too high for most of the regions of the world [ Liu et al., 2016 ]. Many studies found that appropriate levels of EFR vary across the river regimes considerably [ Pastor et al., 2014 ].

3.3. Cumulative abstraction to demand ratio – considering temporal variations

In many areas of the world, water scarcity is seasonal, i.e., it only occurs in some months of the year, while there may be enough water on an annual basis. Given this situation, some water scarcity assessments have attempted to take the seasonality into consideration. For example, Alcamo and Henrichs [2002] took into account low river flows in computing a version of the criticality ratio. Another example is the Cumulative Abstraction to Demand (CAD) ratio devised by Hanasaki et al. [2008] . The index was intended to apply the results of global hydrological models, which are able to simulate river discharge and water abstraction at a daily time step. This index is expressed as the ratio of the cumulated daily water abstraction from rivers to the cumulated daily potential water demand (i.e. consumptive water requirement for agricultural, industrial, and domestic use) for a specific year. Recent studies have also been conducted on monthly scale [ Wada et al., 2011 ; Hoekstra et al., 2012 ; Brauman et al., 2016 ]. It is assumed that if the ratio falls below unity, water scarcity can occur. Hanasaki et al. [2008] demonstrated that CAD is low in Southeast Asia and the Sahel due to periodic, severe water shortage in the dry season, which is often overlooked in the assessments adopting classical water scarcity indicators. CAD provides useful insights for assessing the impact of climate change on water resources. In some areas, annual total runoff is projected to increase due to global warming water scarcity may appear to diminish when the withdrawal to availability ratio is used, which may be misleading. In this case CAD presents a more realistic view of water scarcity because it takes into account the increase in water scarce conditions during the dry months [ Hanasaki et al., 2013 ; Haddeland et al., 2014 ]. However, the high demand for data and complex computational tasks have limited the use of this water scarcity assessment approach.

3.4. LCA-based water stress indicators

Water scarcity assessment has been introduced in Life Cycle Assessment (LCA) to address water consumption and its environmental impact since 2008 [ Frischknecht et al., 2009 ; Pfister et al., 2009 ; Berger et al., 2014 ] and is continuously expanded. The main methods used in LCA can be grouped into midpoint and endpoint indicators and address scarcity on watershed level [ Kounina et al., 2013 ]. Midpoint indicators address water scarcity as a water resource problem, while endpoint methods try to quantify potential impacts on human health or ecosystem quality, which goes beyond scarcity but includes vulnerability and resilience. LCA methods address water scarcity at the midpoint level.

In LCA, water consumptive use to availability ratios are used to derive an indicator based on various functions, such as logistic or exponential [ Kounina et al., 2013 ]. The most widely used indicator is the water stress index (WSI) [ Pfister et al., 2009 ]. Recognizing that both monthly and annual variability of precipitation may lead to increased water stress during a specific period, a variation factor is introduced to calculate the ratio, which differentiates watersheds with strongly regulated flows. Considering water stress is not linear with regards to water consumptive use and water availability ratio, an adjusted water stress index is calculated with a logistic function to achieve continuous values between 0 and 1, while 0.1, 0.5 and 0.9 are assigned as thresholds for moderate, severe and extreme water scarcity. The water stress index is served as a general screening indicator or characterization factor for water consumption in Life Cycle Impact Assessment. As the LCA based water scarcity assessment focuses on impact assessment of water use, the indicator has not been separately used for water scarcity assessment.

3.5. Integrated water quantity-quality-environment flow in the water scarcity assessment

The water scarcity indicators developed have mainly considered water quantity. Zeng et al. [2013] developed an integrated indicator, which is expressed as the sum of a quantity-induced indicator and a quality-induced indicator. The quantity-induced water scarcity indicator follows the criticality ratio approach, and is defined as the ratio of the water withdrawal to freshwater resources in a specific region during a certain period. The quality-induced water scarcity indicator is defined as the ratio of grey water footprint to freshwater resources. Here, grey water footprint is defined as the volume of freshwater that is required to assimilate the load of pollutants based on natural background concentrations and existing ambient water quality standards [ Hoekstra et al., 2011 ]. It does not have the same meaning as the terms used in urban water management, for which grey water refers to the water comes out of the shower or sink. This indicator combining quantity- and quality-induced water scarcity was illustrated by analyzing the water scarcity in China. The result shows that the northern parts of the country are suffering from both quantity- and quality-induced water scarcity ( Fig. 2 ). In southeast, quality-induced water scarcity is dominant due to the heavy water pollution. The results imply that northern China has a much bigger burden to deal with the water scarcity problems, while for other provinces, quality-induced water scarcity is a grand challenge.

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Water scarcity assessment for different provinces with the quantity-quality indicator approach. This map was generated by J Liu based on the approach of Zeng et al. [2013] .

On the basis of Zeng ’s indicator, EFR was further added in the water scarcity assessment, resulting in a quantity-quality-EFR (QQE) approach [ Liu et al., 2016 ]. It is structured with multi-components in the indicator: S quantity (EFR)|S quality . The QQE approach was first used for the Huangqihai River Basin in Inner Mongolia, China. The QQE water scarcity indicator in this river basin is 1.3(26%)|14.2, indicating that the basin was suffering from scarcity problems related to both water quantity (1.3 is larger than the threshold of 1.0) and water quality (14.2 is far larger than the threshold of 1.0, indicating a serious water pollution condition) for a given rate of 26% of EFR.

The QQE water scarcity indicator provides an easy to obtain and to understand measurement that contains the information of water quantity and quality status, as well as EFR. The procedure can be adapted to any other areas in the world to provide a comprehensive assessment on water scarcity. By specification, one can also use the percentage of EFR to indicate any other levels of ecological habitat status. However, the QQE indicator has some limitations. The indicator is not as straight forward as the existing indicators, which use a single value to indicate the status of water scarcity. It requires some professional knowledge to understand the indicator and interpret the information contained.

4. Where are we now?

Many global assessments of water scarcity have been conducted so far ( Figure 3 ). The spatial resolution ranges from country, region to grid cell. In general, all the indicators pointed out that the areas in the middle to low latitudes of the northern hemisphere have a high level of water scarcity. It is noticed that the physical and economic water stress ( Fig 3C ) and water poverty index ( Fig 3D ) also identified the severe water scarcity problem in almost all African countries. This is attributed to the lack of economic capacity to build water infrastructure as well as poverty, which have hindered these countries to access their water resources that are often physically abundant. Despite the relevance of concerning economic factors in water scarcity assessment, the complexity such concern brought to the assessment increases greatly. There is no consensus on which social and economic factors should be included, and for different countries and regions, these factors can be different. To keep the objectivity and simplicity, all the other water scarcity indicators developed so far have been based solely on physical quantity of water availability and use.

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Spatial distribution of water scarcity from different assessments. Below is a list of references for Fig. 3 A–H and the indicator used in relation to Table 1 . A: Water shortage (modified from Kummu et al., [2010] ); B: Water stress (modified from Wada et al., [2011] ); C: Physical and economic water scarcity (modified from Seckler et al., [1998] ); D: Water poverty index (modified from World Resources Institute [2006] ; Sullivan et al., [2002] ); E: Green-blue water scarcity (modified from Kummu et al., [2014] ); F: Monthly blue water stress (modified from Mekonnen and Hoekstra, [2016] ); G: Cumulative abstraction to demand ratio (modified from Hanasaki et al., [2013] ); H: LCA-based water stress indicator (modified from Pfister et al. [2009] ). Note: all maps were redrawn by authors based on original data from the sources given above, except water poverty index, which was modified from a softcopy map. Further, legend colors in some maps are modified for consistency.

One of the main outcomes of water scarcity assessments is estimates of number of people affected by water scarcity. Results differ when different indicators are used, even for the same indicator from different reference sources ( Figure 4 ). For example, estimates using the criticality ratio with a threshold of 40% tend to be higher than those based on the Falkenmark indicator with a threshold of 1000 m 3 /person/year. Variations in number of people living in water scarcity with the same indicator are partially related to different spatial resolutions in the assessment. In general, the higher spatial resolution results in larger number of people suffering from water scarcity ( Fig. 3 ). This is because the high spatial resolution can better reflect the water scarcity situation in urban areas with high population concentration [ Vörösmarty et al., 2010 ]. However, high spatial resolution tends to underestimate human capacity to bring water from outside into cities. Also, including green water will enlarge the quantity of water availability for a geographical unit (e.g., country, region), resulting in smaller estimates of people living in water scarcity. Respecting the EFR by leaving sufficient water in steams, on the other hand, results in larger estimates, because it reduces the water resources available for humans. Furthermore, including water quality can lead to substantial increase in the magnitude of water scarcity, as the poor water quality can make available water not usable. Overall, the estimated numbers from different indicators suggest that between 1.5 and 2.5 billion people were living within areas exposed to water scarcity around the year 2000 ( Fig. 4 ), but water footprint based water scarcity assessment increases the number to 4 billion [ Mekonnen and Hoekstra, 2016 ]. When water stress and water shortage are assessed in a combined manner, altogether 3.8 billion lived under some degree of water scarcity in 2005 [ Kummu et al., 2016 ]. The numbers are projected to increase substantially up to at least 2050 in association with the peak of world population. Current analyses suggest that thereafter the numbers may decline.

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Number of people suffering from water scarcity assessed with the average annual water availability per capita (1000m 3 /capita/year) and water use to availability ratio (40%). The marks show the estimates from different studies. Specific estimates include: 1.2 billion [ Hayashi et al., 2010 ], 1.4 billion [ Arnell, 2004 ], 1.6 billion [ Alcamo et al., 2007 ; Arnell et al., 2011 ; Gosling and Arnell, 2016 ], 1.7 billion [ Revenga et al., 2000 ], and 2.3 billion [ Kummu et al., 2010 ]. But the number may be quite different when other indicators are used, e.g. Mekonnen and Hoekstra [2016] estimated that 4 billion people live under conditions of severe water scarcity at least 1 month of the year between 1996 and 2005.

5. Future research challenges and directions

5. 1. validating water scarcity indicators.

The indicators presented in this paper have been used by scientists to compare their values in one region versus another in order to estimate the relative level of water scarcity. However, so far very little efforts have been made to prove how these indicators appropriately reflects the water scarcity quantitatively, and how the thresholds reasonably classify water scarcity. All the indicators and their thresholds have been determined based on expert judgments. The expression "to validate indicators" generally means to support or corroborate on a sound or authoritative basis [ Bockstaller and Girardin, 2003 ; Dauvin et al., 2016 ]. An essential problem in validating these indicators has been the difficulty in identifying an independent variable for water scarcity. Alcamo et al. [2008] used the “frequency of occurrence of drought-related crises” in three large river basins as an independent variable. Values of this metric were determined from media-content analysis by Taenzler et al. [2008] . With estimates of this variable, it was possible to test the validity of various water scarcity indicators. Using modelling data from a 15-year period, it was found that 6 out of 14 different tested water scarcity indicators were statistically related to the occurrence of drought-related crises [ Alcamo et al., 2008 ]. This initial work indicates that it may be possible to validate indicators, identify their appropriate range of application, and test scarcity thresholds. Research in this direction would strengthen the scientific basis of estimating water scarcity and perhaps accelerate the development of more useful indicators.

5.2. Incorporating water quality in water scarcity assessment

As poor water quality has intensified the pressure on water resources [ Bayart et al., 2010 ], including more specific water quality classes for ecosystem and human uses is necessary to enhance the pertinence of water scarcity assessments. Water quality is typically expressed as concentration of certain pollutants. The most considered pollutants influencing water quality have been nutrient emissions, typically nitrogen and phosphorous, and to a lesser extent, COD [ Björklund et al., 2009 ; Liu et al., 2012 ]. The assessment of water quality induced water scarcity is sensitive to the pollutant selected. In order to include water quality data in water scarcity assessments, suitable data need to be collected covering a range of water quality parameters. Often, the list of parameters to be considered may be guided by the objectives of a study, i.e. specific requirements for drinking water are different from that for irrigation water. For an aggregated water scarcity assessment, it would be ideal to use an aggregated water quality indicator that can reflect the overall water quality status. Building such an indicator with a broad applicability is a challenge faced in the future water scarcity assessment.

Another challenge in incorporating water quality is that the availability of water quality data is very heterogeneously distributed over the world and varies tremendously between regions with huge data gaps in developing countries. The United Nations Environment Programme Global Environment Monitoring System (GEMS) Water Programme is a multi-faceted water science centre oriented towards building knowledge on inland quality issues worldwide ( http://www.unep.org/gemswater/ ), which is still very limited considering the large surface of the earth. The GEMS/Water Programme, established in 1978, is the primary source for global water quality data. The related water quality database, GEMStat, is designed to share surface and ground water quality data sets collected from the GEMS/Water Global Network, so far including more than 3,000 stations ( http://gemstat.org/ ). For Africa, data found in scientific literature were very dissimilar and disparate, most published data were aggregated over long time periods and/or over several sampling stations [ UNEP, 2016 ]. Furthermore, specific locations of sampling stations were usually not available and the selection of parameters was restricted. In this context, global scale water quality models could be used as a complementary approach to fill data gaps of relevant parameters in time series and in regions where no reliable data exist. Since a model is a simplified representation of the real world system, its credibility is ensured by its model performance in terms of validation and testing against measured data. It is worth mentioning that the WaterGAP3 modeling framework has been enhanced by a large-scale water quality model WorldQual in order to estimate pollution loadings and in-stream concentration for a variety of parameters (e.g. Voß et al., [2012] ; Reder et al., [2013 , 2015 ]). Many crop models, such as GEPIC, have both components of hydrology and pollution loading [ Liu and Yang, 2010 ; Liu et al., 2013a ]. With their ability to calculate water availability, water use, and water quality parameters, the modeling framework is promising for simultaneously considering water quantity and water quality in water scarcity assessment.

5.3. Incorporating environmental flow requirements in water scarcity assessment

Rudimentarily, EFRs has been incorporated in water scarcity assessment by assuming a fixed percentage of river flow for EFR, ranging from 80% of the annual flow uniformly all over the globe [ Hoekstra et al., 2012 ] to specific proportions in given locations [ Smakhtin et al., 2004 ; Rockström et al., 2009 ; Gerten et al., 2011 ; Liu et al., 2016 ]. However, in the natural system, EFRs vary across flow regimes and seasons. E.g., Pastor et al. [2014] found that EFRs ranged between 25% and 46% of mean annual flow. This suggests an importance to incorporate locally pertinent EFR for a proper assessment of water scarcity status.

The future studies that estimate EFRs should consider a range of methodologies that account for seasonal variations and flow regimes in different parts of the globe [ Gerten et al., 2013 ]. Different approaches have been developed for assessing the EFRs for different river regimes. E.g., Laize et al. [2014] and Schneider et al. [2013] presented a comprehensive approach to quantify ecological risk as a result of flow alterations in terms of the deviation from natural flow conditions. They assessed hydrological alterations from natural flow dynamics caused by anthropogenic water use and dam operations and by using a subset of 12 different parameters chosen from the list of Indicators of Hydrological Alteration [ Richter et al., 1996 , 1997 ]. This approach considers different flow characteristics and describes non-redundant departures from the natural flow regime. In addition, changes in average magnitude and variability of each parameter are considered, and therefore, in total 24 sub-indicators are taken into account. This indicator system could be used to account for EFRs across regions in water scarcity assessment.

5.4. Temporal and spatial scales of water scarcity with consideration of green water and virtual water

In water scarcity assessments, the selection of spatial scale (or unit of analysis) is important, and difficult too. It has considerable impacts on results, as shown earlier ( Fig. 3 ) and by other studies [ Salmivaara et al., 2015 ; Perveen et al., 2011 ]. Most of the water scarcity assessments are conducted on a grid scale (30 arc-min, i.e. 50 km resolution near the equator), while for addressing water scarcity, country, basin or sub-basin (e.g. food production unit) scales are more policy relevant. A detailed study of the impact of different spatial scale on water scarcity assessment would be needed.

Most water scarcity indicators are measured on annual time scale. With significant intra-annual variations in water use and availability, it is important to understand when water is available and when it is needed within a year. Thus, the introduction of a monthly scale assessment could provide information whether there is enough water for each month to fulfill the requirements.

Other relevant aspect to temporal scale is the impact of inter-annual variability of water availability and water requirements on scarcity measures. Veldkamp et al [2015] found that on the shorter time scales (up to 6–10 years) the climate variability is the dominant factor influencing water scarcity while on the longer time scales the socioeconomic development is more important factor. Brauman et al. [2016] found that watersheds that appear to be moderately depleted on an annual time scale are almost uniformly heavily depleted at seasonal time scales or in dry years. Hence, the assessment of inter-annual variability adds important insights on the understanding of water scarcity.

It also needs to be pointed out that the whole population living in a region (e.g. country, watershed) are often not equally been impacted by water scarcity. For example, people with a higher income may be less affected by water scarcity than people with a lower income. Also the rural and urban population may be affected differently. For this reason, it would be more indicative to consider the possibly different effects of socio-economic conditions on the people residing in a water scarcity region. Adopting a probabilistic approach could reduce the scaling effects. This, however, requires more detailed information on the socio-economic conditions of people in the region.

Green water is an important component of water resources. However, in the water scarcity assessment, it has been rarely considered due mainly to different measurements of green and blue water resources, the former is in storage (in unsaturated soil) and the latter is flow measured on annual basis. The work which did consider green water only accounted for the portion that has been actually used by crops [ Rockström et al., 2009 ; Gerten et al., 2011 ]. This greatly underestimates green water resources. One possible approach to remedy the problem is to count for accumulated soil moisture on an annual basis on the land surface regardless of if it is used or not by crops or other plants. It needs to be pointed out that the validity to incorporate green water is sometime questioned in water resources management [ Bogardi et al., 2013 ]. One major reason is that green water is not part of the water budget that could be easily reallocated to other use. Our opinion is that soil moisture (green water) is an important resource which should be appropriately incorporated in the water availability accounting.

Most of the water scarcity indicators previously developed only account for local water resources and local water demand. But recent research advances have revealed that previously unrecognized global forces may drive local-scale water problems [ Vörösmarty et al., 2015 ]. Much of the global water use and pollution is from the production of commodities for global and regional trade, which embodies a large amount of virtual water flows and influences local water scarcity [ Zhao et al ., 2015 ; Hoekstra and Mekonnen, 2016 ; Vörösmarty et al., 2015 ; Zhao et al., 2016 ]. Long distance water transfer systems also impact the local water scarcity situations in both the sourcing and destination regions [ Liu et al., 2013b ]. There is a need to integrate virtual water flows and water transfers in the water scarcity analysis.

5.5. Need for collaboration between hydrological, water quality, aquatic ecosystem science and social science communities in water scarcity assessment

There are crucial connections between water availability and water quality [ Jury and Vaux, 2005 ] and both have been associated with human health [ Myers and Patz, 2009 ], food security [ Rockström et al., 2009 ; Simelton et al., 2012 ] and for sustaining native biodiversity and integrity of aquatic ecosystems [ Poff et al., 1997 ; Richter et al., 1997 ]. This means that assessments of water availability and quality should be conducted in a consistent way so that relevant dependencies between availability and quality are accounted for. This will require the integration of water quality and ecological parameters, and processes (and feedbacks between them) into water availability assessment models. This can only be achieved through sustained integration of the water availability modelling community with the water quality and ecological modelling communities.

Integrating these communities represents the first, and an important step, towards developing a comprehensive understanding of the susceptibility of global water availability and quality to change. Beyond this, the relevant communities will need to develop improved hydrological models at the global scale that consider both water quantity and quality. Reliable observations of water quality at sufficient spatial resolution across the globe will also be needed to validate the models.

As noted above, water scarcity indicator thresholds are artificial and ‘best guess’ rather than evidence-based. There are limitations about the utility of indicators [ Fekete and Stakhiv, 2014 ] given the complexity of water management challenges that these indicators intend to support. These indicators are generally insufficient to incorporate the complex socio-economic backdrop driving water demands and they do not address the alternative pathways such as the choices of water produced. Fostering interdisciplinary or even trans-disciplinary research in water scarcity studies as well as the integration of stakeholders offers the possibility of clear frameworks and hence the improvement of systems’ understanding. For example, factors affecting water demand, such as changes in lifestyle, perceptions of water scarcity, and attitudes towards water use, are routed in social science understandings of how these factors can be influenced by government policy and social norms [ Wolters, 2014 ]. Moreover, a novel opportunity exists to make social science more effective in improving water management and understanding the drivers of water scarcity [ Lund, 2015 ].

  • We provide a comprehensive review of water scarcity indicators and reflect on their relevance in a rapidly changing world
  • There is a need to incorporate green water, water quality and environmental flow requirements in water scarcity assessment
  • Integrated approaches are required to capture the multi-faceted nature of water scarcity

Acknowledgments

This study was supported by the National Natural Science Foundation of China (41571022), National Science Fund for Distinguished Youth Scholars (41625001), the Beijing Natural Science Foundation Grant (8151002), the National Natural Science Foundation of China (91325302, 91425303), the National Science and Technology Major Project (2015ZX07203-005). The work on the paper was developed within the framework of the Panta-Rhei Research Initiative of the International Association of Hydrological Sciences (IAHS). The present work was partially developed within the framework of the Panta Rhei Research Initiative by the working group “Water Scarcity Assessment: Methodology and Application”. All data used for this paper are properly cited and listed in the references. This is a review article and we do not generate data except for those used in Figure 2 . Users can contact the correspondence author when they need water scarcity data in this figure.

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Global water scarcity including surface water quality and expansions of clean water technologies

Michelle T H van Vliet 1,2 , Edward R Jones 1 , Martina Flörke 3 , Wietse H P Franssen 2 , Naota Hanasaki 4 , Yoshihide Wada 5,1 and John R Yearsley 6

Published 26 January 2021 • © 2021 The Author(s). Published by IOP Publishing Ltd Environmental Research Letters , Volume 16 , Number 2 Citation Michelle T H van Vliet et al 2021 Environ. Res. Lett. 16 024020 DOI 10.1088/1748-9326/abbfc3

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1 Department of Physical Geography, Utrecht University, P.O. Box 80.115, 3508 TC, Utrecht, The Netherlands

2 Water Systems and Global Change Group, Wageningen University, P.O. Box 47, 6700 AA, Wageningen, The Netherlands

3 Ruhr-Universität Bochum, Universitätsstr. 150, DE-44801, Bochum, Germany

4 National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba, Japan

5 International Institute for Applied Systems Analysis (IIASA), Schlossplatz 1, A-2361, Laxenburg, Austria

6 Department of Civil and Environmental Engineering, University of Washington, Seattle, WA, 98195, United States of America

Michelle T H van Vliet https://orcid.org/0000-0002-2597-8422

Naota Hanasaki https://orcid.org/0000-0002-5092-7563

Yoshihide Wada https://orcid.org/0000-0003-4770-2539

John R Yearsley https://orcid.org/0000-0002-2630-9589

  • Received 5 May 2020
  • Accepted 9 October 2020
  • Published 26 January 2021

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Method : Single-anonymous Revisions: 2 Screened for originality? Yes

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Water scarcity threatens people in various regions, and has predominantly been studied from a water quantity perspective only. Here we show that global water scarcity is driven by both water quantity and water quality issues, and quantify expansions in clean water technologies (i.e. desalination and treated wastewater reuse) to 'reduce the number of people suffering from water scarcity' as urgently required by UN's Sustainable Development Goal 6. Including water quality (i.e. water temperature, salinity, organic pollution and nutrients) contributes to an increase in percentage of world's population currently suffering from severe water scarcity from an annual average of 30% (22%–35% monthly range; water quantity only) to 40% (31%–46%; both water quantity and quality). Water quality impacts are in particular high in severe water scarcity regions, such as in eastern China and India. In these regions, excessive sectoral water withdrawals do not only contribute to water scarcity from a water quantity perspective, but polluted return flows degrade water quality, exacerbating water scarcity. We show that expanding desalination (from 2.9 to 13.6 billion m 3 month −1 ) and treated wastewater uses (from 1.6 to 4.0 billion m 3 month −1 ) can strongly reduce water scarcity levels and the number of people affected, especially in Asia, although the side effects (e.g. brine, energy demand, economic costs) must be considered. The presented results have potential for follow-up integrated analyses accounting for technical and economic constraints of expanding desalination and treated wastewater reuse across the world.

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1. Introduction

A growing worldwide population strongly increases the demands for clean water for different sectoral water uses (e.g. irrigation, domestic, energy, manufacturing uses) (Biswas and Tortajada 2018 ). Climate change induced increases in the frequency and intensity of hydro-climatic extremes (e.g. droughts, floods) (Dankers et al 2014 , Prudhomme et al 2014 , Trenberth et al 2014 ), combined with increasing intensification of agriculture, industrialisation, urbanisation, and water extractions and uses, aggravate water quality deterioration, particularly in developing countries (Macdonald et al 2016 , UNEP 2016 , Sinha et al 2017 ). These changes will challenge sustainable management of 'clean accessible water for all', one of the UN Sustainable Development Goals (SDGs) for 2030 (UN 2015 ).

So far, water scarcity assessments have focussed mainly on water quantity (Schewe et al 2014 , Liu et al 2017 , Cui et al 2018 ). A widely used index of water scarcity or water stress considers the proportion of the freshwater use (withdrawal) relative to the available freshwater resources (Liu et al 2017 ). This indicator has been used for several scientific studies (Kummu et al 2016 , Liu et al 2017 , Vanham et al 2018 ) and is also presented as SDG-indicator 6.4.2 for estimating levels of water stress (UN 2015 ). Previous work by Vanham et al ( 2018 ) evaluated the shortcomings of this water scarcity indicator, including the absence of water quality, the lack of consideration of unconventional water resources, and the weak temporal (annual) and spatial (country) resolutions used in most water scarcity assessments (Vanham et al 2018 ).

It is imperative that we understand regional hotspots of water scarcity in terms of both water quantity and quality, as the usability of water for human purposes and ecosystem health depends on both sufficient water quantity and suitable water quality (van Vliet et al 2017 ). Earlier studies used the water poverty index combining water quantity and quality data (Sullivan et al 2003 ) or included water pollution drivers in calculations of threat indices to human water security and biodiversity (Vörösmarty et al 2010 ). For Chinese cities and river basins (Zhao et al 2016 , Liu et al 2017 ), the ratio of total water demands to freshwater availability has been combined with the grey water footprint (Hoekstra and Mekonnen 2012 ) (i.e. the amount of water required to dilute pollutants in wastewater to sufficiently meet environmental water quality standards). Following on this concept, an indicator of water scarcity has been developed including water quality requirements for different sectoral water uses (van Vliet et al 2017 ). However, an assessment of water scarcity accounting for water quality and clean water technologies is still lacking, in particular at the large scale.

Typically, water scarcity solutions focus on decreasing sectoral water uses (e.g. improved water use efficiencies) or by increasing water availability (e.g. increasing reservoir storage capacity). These solution options have been included in earlier water scarcity assessments (e.g. Ward et al 2010 , Wada et al 2014a , Jägermeyr et al 2015 ). Clean water technologies suiting both the water quantity and water quality demands, such as desalinated water use and treated wastewater reuse, are fast-growing (Elimelech and Phillip 2011 , Gude 2017 , Jones et al 2019 ). Both options are considered as a key component to reduce water pollution and freshwater scarcity globally (SDG targets 6.3 and 6.4) (UN 2015 ). While some first steps have been made to implement seawater desalination in water scarcity quantifications (Oki and Kanae 2006 , Hanasaki et al 2016 ), these assessments have ignored desalination of inland (brackish, river) waters and other sources (e.g. wastewater, brine), which together contribute to almost 40% of the desalination water use worldwide (Jones et al 2019 ). Furthermore, the desalination data used in previous studies did not consider sector-specific uses of desalinated water. Another previous study of Parkinson et al ( 2019 ) focused on improved water access, treatment and efficiencies towards the SDG6 targets using an integrated assessment modelling approach, but water quality conditions were disregarded.

Here we fill in the knowledge gap by presenting global hotspots of water scarcity driven by both surface water quantity and water quality issues, and quantify expansions in desalination and treated wastewater reuse to reduce the number of people suffering from water scarcity as required by UN's SDG6.

2.1. Water scarcity indicators and framework

We developed new indicators and a globally applicable model framework of water scarcity including a water demand versus supply dimension from both a surface water quantity and water quality perspective (figure 1 ). Our framework includes global gridded simulations at 0.5° × 0.5° spatial resolution of surface water availability and sectoral water use (section 2.2 ), surface water quality and sector water quality requirements (section 2.3 ) and spatially-explicit data of desalination and treated wastewater reuse capacities (section 2.4 ). We focus on these two water technologies, because they are fast-growing technologies suiting both water quantity and quality demands (Elimelech and Phillip 2011 , Gude 2017 ) and because they are considered as a key component to reduce freshwater scarcity globally (UN 2015 ). Next to this, wastewater treatment impacts are also included in the modelling of pollutant loadings and hence in surface water quality concentrations. The focus of this water scarcity assessment is on surface water resources, and with particular focus on impacts of surface water quality, desalination and treated wastewater reuse on water scarcity levels. We do not include groundwater resources in our study, given the current lack of a globally-applicable groundwater model accounting for both water quality and quantity.

Figure 1.

Figure 1.  Water scarcity framework and three water scarcity indicators: 1. water scarcity based on only quantity (WS), 2. water scarcity including both water quantity and water quality (WSq); and 3. water scarcity based on both water quantity and quality, and including desalination and treated wastewater reuse (WSq _ desal + wwr ).

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Water scarcity was quantified using three different water scarcity indicators: 1) water scarcity based on only surface water quantity (WS); 2) water scarcity including both surface water quantity and water quality for different sectoral uses (WSq); and 3) water scarcity based on both surface water quantity and quality, and including desalination of various sources (sea water, inland resources) and treated wastewater reuses per sector (WSq _ desal + wwr ). These three indicators are briefly discussed below and in more detail (including their equations) in the supplementary section 1 (available online at stacks.iop.org/ERL/16/024020/mmedia ).

Water scarcity based only on quantity (WS) is calculated as the ratio of water withdrawals for all sectors to surface water availability ('criticality ratio'), accounting also for environmental flow requirements (EFRs). The 'criticality ratio' is a widely use approach (Alcamo et al 2003b , Raskin et al 1997 , Liu et al 2017 , Vanham et al 2018 ), which has also been adopted by the UN SDG-indicator 6.4.2. (for details see supplementary section 1.1 and supplementary equation 1).

Water scarcity including both water quantity and water quality (WSq) is estimated by using the ratio of the sectoral water withdrawals of acceptable quality to the water availability. Under conditions that a water quality constituent i does not meet the sector water quality requirements for sector j ( C i > C max i,j ) we quantify the additional water needed to obtain acceptable water quality by dilution (dq i,j ). For this, we estimate for each water use sector the most critical water quality constituent resulting in the highest dilution water demands (dq max j ). Here we follow on from the concepts of grey water footprint and previous work (Hoekstra and Mekonnen 2012 , van Vliet et al 2017 , Ma et al 2020 ), but focussing on dilution of water withdrawn for specific-sector uses rather than total water availability. For thermoelectric water withdrawals, which largely depend on water temperature as the critical water quality constituent, we used spatially-explicit values of maximum permitted water temperature for cooling water use (see supplementary section 3.5, supplementary table 1). Where the water temperature exceeds permissible levels, we calculate the extra surface water withdrawal needed to dilute thermal effluents from power plants (i.e. dissipate the same waste heat). This is in line with the increase in water demands for power plant cooling under higher water temperatures as quantified in earlier work (Koch and Vögele 2009 , van Vliet et al 2012 ). Additional dilution water demands can also be estimated to obtain acceptable salinity, for instance, for irrigation uses. This dilution water suiting water quality for sectoral use can in principle originate from various sources (e.g. treated (waste) water or groundwater). In our global assessment we do however not specify the origin of these alternative water resource, but we quantify the potential dilution water requirement needed to obtain acceptable quality. This results in a calculated additional 'pressure' on the water system (higher water scarcity levels) in case water quality does not meet certain sectoral water quality requirements. Our water scarcity approach explicitly accounts for different quality requirements by different intended uses (for details see supplementary section 1.2 and supplementary equation 2).

We further developed this water scarcity indicator to account for spatially-explicit desalination uses and treated wastewater reuses. We distinguish between desalinated water from 'new' sources (i.e. beyond what is available from inland waters, e.g. seawater) and 'existing' (inland) sources (brackish water, river waters) per water use sector (see equation 1; for details see supplementary section 1.3). Both desalination and treated wastewater are subtracted from the sectoral water demand and hence also cause a reduction in the volume of water required for dilution of water to obtain an acceptable quality (dq).

Where WSq desal + wwr = water scarcity including water quality, desalination and treated wastewater reuse [−]; D = water withdrawal for sector j [m 3 s −1 ]; Q = water availability [m 3 s −1 ]; EFR = environmental flow requirements [m 3 s −1 ]; dq i,j = extra water withdrawals for dilution to obtain acceptable quality for sector j and water quality constituent i [m 3 s −1 ]; dq max j = maximum required water withdrawals for dilution to obtain acceptable quality for sector j based on the most critical water quality constituent [m 3 s −1 ]; N j = desalinated water of 'new' sources (e.g. seawater, brine) for sector j [m 3 s −1 ]; E j = desalinated water of 'existing' sources (inland brackish, river water resources) used for sector j [m 3 s −1 ]; W j = treated wastewater reuse for sector j [m 3 s −1 ]; C i = actual water quality level of water quality constituent i [unit depends on water quality constituent considered, e.g. mg l −1 for concentrations, °C for water temperature]; C max i,j = maximum water quality threshold for water quality constituent i for water use sector j [e.g. mg l −1 ,°C].

All water scarcity calculations are at 0.5° × 0.5° spatial resolution globally and with a monthly timestep, focussing on the period of 2000–2010. We identified water scarcity levels higher than 0.4 as 'severe water scarcity' in line with previous work (Liu et al 2017 , Hanasaki et al 2018 ), facilitating comparisons with previous studies. The average population under 'severe' water scarcity was quantified by combing our monthly water scarcity calculations with gridded (0.5°) population data (Goldewijk et al 2005 , 2010 ).

2.2. Global water resources and sectoral water use modelling

For the water quantity component of our water scarcity framework we used global gridded simulations of surface water availability (i.e. discharge), sectoral water use (i.e. withdrawal and consumption) at 0.5° × 0.5° spatial resolution and on a monthly time step for 1979–2010 from four global hydrological models: PCR-GLOBWB (van Beek et al 2011 , Wada et al 2011 , 2014b , Sutanudjaja et al 2018 ), H08 (Hanasaki et al 2008 ), WaterGAP2 (Döll et al 2003 , Alcamo et al 2003a , Flörke et al 2013 , Müller Schmied et al 2016 ) and VIC (Liang et al 1994 , Lohmann et al 1998 , Hamman et al 2018 , Droppers et al 2019 ). We used simulated actual water withdrawal and consumption for the main water use sectors irrigation, domestic, manufacturing and thermoelectric water uses. These global hydrological models were selected because of their ability to simulate both water availability and sectoral water use on a global scale. Multi-model mean results were calculated to account for uncertainties in water availability and sectoral water use (withdrawal and consumption) simulations. EFRs were calculated using the monthly variable flow method (Pastor et al 2014 ), on the multi-model average discharge. For further details and results on the global water resource and water use modelling we refer to supplementary section 2.

2.3. Global water quality modelling and sector water quality requirements

The water quality component of our water scarcity framework accounts for surface water temperature, salinity (total dissolved solids; TDS), organic pollution (biochemical oxygen demand; BOD) concentrations), total nitrogen (TN) and total phosphorous (TP) concentrations. These water quality constituents are selected because they are key in constraining different sector water uses and ecosystem health (Scheffer et al 2001 , von der Ohe and Liess 2004 , Dumont et al 2012 , Herbert et al 2015 ). In addition, most of these water quality constituents are also part of SDG indicator 6.3.2 ('Proportion of bodies of water with good ambient water quality').

We developed a process-based global gridded surface water quality model to simulate surface water temperature, salinity (TDS concentrations), and organic pollution (BOD concentrations) using the approaches described in supplementary section 3. This water quality model was applied on 0.5° × 0.5° spatial resolution globally and monthly timestep for the period 1979–2010. Simulated return flows from the global hydrological models per water use sector (supplementary section 2, supplementary figure 3) were calculated and used as input to estimate pollutant loadings for the surface water quality modelling. Thermoelectric return flows were used to simulate impacts of heat effluents from power plants on surface water temperature. For calculating TDS loadings, irrigation and manufacturing return flows, together with population numbers and TDS excretion rates were used. For organic pollution (BOD) loadings, we used manufacturing return flows, population and livestock numbers, and excretion rates per capita and livestock type (cattle, chickens, ducks, goats, pigs and sheep). Next to this, pollutant loadings were calculated including the country-based fractions of wastewater treatment types (primary, secondary, tertiary and advanced treatment) and removal efficiencies per pollutant and treatment level (for details see supplementary section 3). In addition, global grid-based (0.5° × 0.5°) simulations of in-stream concentrations of TN and TP were produced with the IMAGE-GNM model (Beusen et al 2015 , 2016 ) (supplementary section 3).

Model validation against observed surface water quality records show that the observed water quality conditions are represented realistically by the global surface water quality model (supplementary figures 5–10 and supplementary section 3 for more details). However, the station density and number of water quality measurements for model validation is low particularly in the relatively dry regions of the world (e.g. parts of Africa, Australia, Asia and Middle East). This limits analyses of the water quality model performances in those regions. Next to this, the uncertainties in the simulated water availability are also highest in particular in these dry regions (supplementary figure 4), which likely also results in higher uncertainties in simulated in-stream concentrations and water scarcity levels. The results of simulated water availability, water quality and water scarcity are therefore masked in the global maps for the very dry regions of the world (with surface water availability less than 1 m 3 s −1 ). These very dry regions contribute to less than 1.6% of the global population.

Water quality requirements for irrigation, domestic, manufacturing and thermoelectric water uses and for ecosystem health used in our water scarcity framework are derived per sector from international standards (supplementary section 3.5). The exception is water temperature for which standards were considered only for energy (thermoelectric) uses and ecosystem health. An overview of the selected water quality thresholds for all water use sectors and selected water quality constituents, as well as the corresponding sources is presented in supplementary table 1.

2.4. Desalination and treated wastewater reuse globally

Desalination capacity was derived from a global spatially-explicit desalination plant database (GWI 2019a ) including results of 15 906 operational desalination plants (supplementary section 4.1). This database accounts for desalinated water use per main water use sector (domestic, manufacturing, energy, irrigation) individually (supplementary figure 12). Our approach thus accounts for sector-specific desalination uses and considering different sources: seawater, inland (brackish, river) sources, brine and wastewater.

A global spatially-explicit dataset of wastewater reuse was developed on 0.5° × 0.5° spatial resolution by downscaling of country data of existing sources (AQUASTAT 2019 , GWI 2019b ) with total gridded population numbers (Klein Goldewijk 2005 , Klein Goldewijk et al 2010 ) as described in more detail in supplementary section 4.2 (supplementary figure 13).

2.5. Expansion in desalination and treated wastewater reuse towards water scarcity mitigation

We quantify how much expansion in desalination and treated wastewater reuse would potentially be required compared to current capacities to 'substantially reduce the number of people suffering from water scarcity' in line with SDG target 6.4. For this final part of the analyses, we focus on water scarcity levels below 0.2 as target towards water scarcity mitigation, because a water scarcity threshold of 0.2 has typically been set as a limit towards 'moderate water scarcity' in contrast to 0.4 representing 'severe water scarcity' (Liu et al 2017 , Hanasaki et al 2018 ). For the analyses of potential expansion in desalination and treated wastewater reuse towards water scarcity mitigation (in line SDG target 6.4) we therefore consider technological expansions aiming at water scarcity levels below 0.2 as an appropriate target. We calculated the required expansion in desalination capacity of both seawater and inland water resources and treated wastewater reuse volume needed under the present (2000–2010) levels to obtain water scarcity levels below 0.2 (WSq _ desal + wwr ≤ 0.2). We consider an increase in desalination capacity (from both sea water and inland surface water resources) required to fulfil sector demands for the domestic, manufacturing and energy sectors, which are the dominant users of desalinated water, accounting for 97% of the world's desalination capacity (Jones et al 2019 ). Expansion in sea water for desalination are constrained to locations proximate to the coastline (<100 km) where increases in seawater desalination are economically feasible and technically viable (Zhou 2005 ). In locations without ready access to seawater, expansions in desalination are assumed to be covered by existing inland water resources (e.g. river water, brackish water), and are constrained by available water resources in contrast to desalination expansion of seawater, which was considered as an 'unlimited source'. Expansion in treated wastewater reuse towards water scarcity reduction is used for the irrigation sector only, which is the dominant user in terms of treated wastewater (Qadir et al 2007 , WWAP 2017 , Zhang and Shen 2017 ). Expansion in treated wastewater reuse capacity were constrained by the available total wastewater produced per gridcell (for details see supplementary section 4.3, supplementary table 3).

3.1. Water scarcity hotspots driven by water quantity and water quality

Our results show that including water quality contributes to an increase in the percentage of the global population currently suffering from severe water scarcity from an annual average of 30% (22%–35% monthly range; only quantity) to 40% (31%–46%; including water quality) for 2000–2010. We focus here on water scarcity levels equal or higher than 0.4, which has typically been set as a limit towards 'severe water scarcity' (Liu et al 2017 , Hanasaki et al 2018 ). Water scarcity levels and hence the number of people affected differ per month, with the largest inter-annual variability in Australia and lowest in North America (figure 2 (a)). Water scarcity intensification by accounting for water quality occurs in South America and Africa, but also in particular in the severe water scarcity regions, such as in South and East Asia (India and China), Middle East, Southern Europe and Mexico (figures 2 (a) and (b)). In most of these water scarcity hotspots we find that water scarcity is driven by a combination of water quantity and water quality issues (figure 2 (c)). Here, excessive sectoral water withdrawals result in high water quantity-driven water scarcity, but polluted return flows degrade water quality, depending also on wastewater treatment efficiencies and capacities.

Figure 2.

Figure 2.  Water scarcity driven by water quantity and water quality issues for 2000–2010. Impacts of water quality on global water scarcity levels including both water quantity and various water quality constituents (water temperature, salinity (TDS), organic pollution (BOD), total nitrogen and total phosphorous concentrations) and bar plots with percentage of population affected by severe water scarcity (a), percentage increase in water scarcity levels by including water quality compared to the approach focussing solely on water quantity (b) and identification of main drivers of water scarcity (water quantity, water quality or combined) (c). Regions with water availability less than 1 m 3 s −1 are masked (white).

While different water quality constituents (pollutants) may have different impacts in terms of constraints for sectoral uses, overall consistent water quality hotspots are identified for organic pollution, salinity and nutrients (figure 3 ). This is due to common pollution sources and contributing sectors, and is in line with previous large-scale water quality assessments covering multiple water quality constituents (Kroeze et al 2016 , UNEP 2016 , Strokal et al 2019 , van Vliet et al 2019 ). In particular in north-eastern China, but also in other parts of central Asia, and parts of the Mediterranean, western US and Mexico, are identified as water quality hotspots regions in terms of high salinity (TDS), organic pollution (BOD) and nutrients (TN, TP) concentrations.

Figure 3.

Figure 3.  Global surface water quality hotspots. Average simulated in-stream concentrations presented for simulated organic pollution as indicated by biochemical oxygen demand (BOD) (a), salinity as indicated by total dissolved solids (TDS) (b), total nitrogen (TN) (c) and total phosphorous (TP) (d) concentrations. Regions with water availability less than 1 m 3 s −1 are masked (white). For details of water quality modelling and validation results see supplementary section 3, and supplementary figures 5–10.

Degraded water quality may result in unsuitability for sectoral water uses, exacerbating water scarcity levels. For the most severe water scarcity hotspots in the world, including eastern China and parts of central Asia, water scarcity is strongly water quality-driven (figure 2 (c)). Here, we see that water scarcity levels increase by an order of magnitude compared to water scarcity based on only water quantity. Exacerbation of water scarcity due to water pollution in China is in line with previous water scarcity studies for this region (Zhao et al 2016 , Ma et al 2020 ). In contrast, in regions with low sectoral water uses and pollution levels and with high water availability (e.g. tropical regions and high latitudes) we find that water scarcity levels, while being low, are mainly water-quantity driven (figure 2 (c)).

We identify for each water use sector and for freshwater ecosystems the main critical water quality constituent that has the strongest contribution in water scarcity intensification. This shows that increases in water scarcity for the energy (thermoelectric) sector are in particular driven by high water temperatures (figure 4 (a)), with higher water scarcity particularly in eastern China, India, US, Europe, and parts of Australia. High salinity (TDS) levels mainly constrain irrigation and manufacturing uses in most regions (figures 4 (b) and (c); for 72% and 77% of area for irrigation and manufacturing, respectively). Domestic water scarcity levels increase due to various critical water quality constituents; high organic pollution (BOD concentrations) in particular in eastern Asia, high TN mainly in Europe, and high salinity (TDS) levels mainly in arid regions (e.g. western US) (figure 4 (d)). Surface water quality thresholds for ecosystem health are exceeded in particular for BOD (45%) and phosphorous (42%) (figure 4 (e)).

Figure 4.

Figure 4.  Main critical water quality constituents contributing to water scarcity for human uses and freshwater ecosystems in water scarcity regions. Maps presenting the water quality constituents that contributed strongest to increases in water scarcity for energy (a), irrigation (b), manufacturing (c), domestic uses (d), and freshwater ecosystems (e).

3.2. Reducing (clean) water scarcity

In a next step, the newly developed water scarcity indicator (WSq _ desal + wwr ) was used to calculate the potential expansion in desalination and treated wastewater reuse towards water scarcity alleviation. From a water resource perspective, the population under severe water scarcity (water scarcity levels equal or higher than 0.4) could potentially be reduced from 40% (31%–46%) to 14% (7.0%–16%) under maximum expansions (figure 5 (a)). This would require a worldwide increase in desalination capacity from 2.9 to 13.6 billion m 3 month −1 and an increase in treated wastewater reuse from 1.6 to 4.0 billion m 3 month −1 . In terms of treated wastewater reuse, the strongest increases are calculated for China and India, which together contribute to 60% of the required expansion in treated wastewater reuse worldwide (figures 5 (b) and 6 (a), (c)). In these densely populated regions, large amounts of wastewater is produced that could potentially be treated and reused to fulfil the high irrigation water demands in these regions. The highest potential expansion in desalination capacity towards water scarcity mitigation is quantified for the USA, China and India and several European countries contributing to water scarcity reduction for domestic and industrial uses (figures 5 (c) and 6 (b), (d)). In some regions, such as India, eastern Asia (China), but also parts of the USA, Europe and other regions, these calculated potential expansions in desalination and treated wastewater reuse are still insufficient to meet the sectoral water demands. This is due to limited available wastewater resources that can be treated and reused, a lack of close access to seawater or limited availability of inland surface resources for desalination. While saline or brackish groundwater desalination could potentially be used in some of these regions, it should be noted that this has been disregarded in our analyses.

Figure 5.

Figure 5.  Impacts of expanding desalination and treated wastewater reuse and required capacity increase towards water scarcity mitigation. Reduction in population under severe water scarcity (a) and required mean expansion in treated wastewater reuse capacity (b) and desalination (c) towards water scarcity mitigation. Circular barplots (b), (c) show results for a selection of 30 countries with highest increase in required total expansion of desalination and treated wastewater capacity towards water scarcity mitigation (in million m 3 month −1 ) and situated in different world regions (NA = North America, SA = South America, EU = Europe, AF = Africa, AS = Asia and Russia, AU = Australia and Oceania).

Figure 6.

Figure 6.  Required potential expansion (absolute and relative increase) in treated wastewater reuse (a), (c) and desalination (b), (d) towards water scarcity mitigation.

4. Discussion and conclusions

We developed a new global water scarcity framework including a water quality dimension and the use of fast-growing clean water technologies suiting both water quantity and quality aspects (i.e. desalination and treated wastewater re-use). Our global study shows that water scarcity levels and percentage of people affected by severe water scarcity are substantially higher when we account also for water quality (on average 40%) rather than solely water quantity (30%). Moreover, we show that water scarcity in most hotspots regions (India, China, Middle East, Mediterranean and Mexico) is driven by a combination of water quantity and water quality issues (figure 2 ). We show that desalinated water use and treated wastewater reuse can potentially strongly reduce the number of people affected by water scarcity (SDG target 6.4), especially in Asia (figures 5 and 6 ). These results are relevant in terms of defining water investment strategies and water resources exploitation potentials on a longer term (Cobbing and Hiller 2019 , Damania et al 2019 ). For instance, in regions where water scarcity is also strongly driven by water quality, investments in clean water technologies or pollution prevention measures (Damania et al 2019 ) would be recommended in addition to traditional measures focusing on water supply management (e.g. reservoir construction).

While our global assessment has been limited to a selection of water quality constituents (i.e. water temperature, salinity, organic pollution, total nitrogen and total phosphorous) relevant for various sectoral uses and ecosystem health, our water scarcity framework could potentially be used to add also other water quality constituents (e.g. pathogens, heavy metals, pesticides, pharmaceuticals and other emerging pollutants). This would require to expand the modelling of pollutant loadings and in-stream concentrations as well as the determination of suitable sectoral water quality standards for additional water quality constituents. The presented estimates of water quality impacts on water scarcity levels and number of people under severe water scarcity could then potentially increase, depending on whether sectoral water quality standards for those water quality constituents are exceeded.

It is important to note that our current water scarcity assessment is limited by the lack of global data for groundwater resources availability and water quality. Previous studies have highlighted a major role of groundwater resources availability and changes on water scarcity levels (Döll 2009 , Foster and Macdonald 2014 , Richey et al 2015 , Damkjaer and Taylor 2017 ). While the focus of our water scarcity assessment is on surface waters and the impacts of surface water quality and water technologies, the water scarcity concept developed in our study has the potential to include groundwater resources. This will provide a more comprehensive understanding of water scarcity, accounting for both surface and groundwater resources from both a water quantity and water quality perspective across different scales. Inclusion of groundwater resources would in particular be important in regions with a relative high contribution of water withdrawals from groundwater resources, such as India (Döll et al 2012 , Wada et al 2014b ), regions where the quality of groundwater resources is deteriorating (Macdonald et al 2016 , Burri et al 2019 , Gleeson et al 2020 ) or where there is a potential for increased sustainable groundwater exploitation, such as in Sub-Saharan Africa (Cobbing and Hiller 2019 ).

Our estimates of expansion in desalination potential towards water scarcity alleviation should be considered as lower bound estimates, as these do not consider potential increases in desalination from brackish groundwater resources. Our study thus identifies the physical boundaries towards water scarcity mitigation from a surface water resources perspective. Next to this, the technical, socio-economic and environmental constraints (Kümmerer et al 2018 ) and side-effects of these technologies must also be considered. Desalination and wastewater treatment are both energy intensive technologies, aggravating greenhouse gas emissions if provisioned from fossil fuels (Martin-Gorriz et al 2014 ), and associated with high economic costs (Parkinson et al 2019 ). The production of by-products also poses problems. For example, the 15 906 desalination plants considered in our study produce at present 4.3 billion m 3 month −1 of brine (i.e. hypersaline concentrate), in addition to the 2.9 billion m 3 month −1 of freshwater for water scarcity alleviation (Jones et al 2019 ). Few economically feasible and environmentally sound management strategies exist for the safe disposal of brine. When disposed back to the source (e.g. seawater), increased salinity and toxicity levels in the receiving body can pose major risks to aquatic ecosystems (Gacia et al 2007 , Palomar and Losada 2011 ). Disposal of brine to inland water resources can also paradoxically increase local water scarcity driven by salinity issues, constraining other sectoral water uses and aquatic ecosystems (Meneses et al 2010 ). Brine production is mainly driven by desalination technology and salinity of feedwater type used, and volumetrically is typically smaller for inland water resources than for desalination of seawater (Jones et al 2019 ). However, suitable and economically viable brine disposal management options are highly important for expanding desalination of inland water resources (Morillo et al 2014 ). For wastewater re-use, health concerns and public perceptions are also potential constraints, particularly for the domestic and irrigation sectors (WWAP 2017 ). Improvements in treatment technologies, coupling with renewable energy sources and resource recovery of 'waste' products provide opportunities for reducing the costs and environmental concerns associated with these technologies.

Achieving 'clean water for all' and 'reducing the number of people suffering from water scarcity', as advocated by SDG6, requires that we expand our focus from solely water quantity solutions (e.g. increasing water use efficiencies and reservoir storage), to measures that contribute to both water quantity and water quality improvements. Moreover, water quality improvements and water scarcity reduction should be sustainable without compromising environmental objectives. In addition to the 'hard infrastructure' clean water technologies, a strong focus on reducing the pollutant emissions (Kümmerer et al 2018 ) is also paramount in meeting the sustainable management of clean and sufficient water for all.

Acknowledgments

Dr Michelle van Vliet was financially supported by a VENI-grant (project no. 863.14.008) of NWO. The Global Environment Monitoring System is kindly acknowledged for supplying observed water quality data worldwide for global water quality model validation purpose. Dr Arthur Beusen is kindly acknowledged for sharing source code for the IMAGE-GNM global nutrient model.

Data availability statement

The data that support the findings of this study are available upon reasonable request from the authors.

Author contributions

MTHvV developed the study, performed the analyses and drafted the manuscript. EJ contributed to the implementation of desalination and wastewater reuse in the water scarcity assessment. WF, MF, NH, YW produced the global hydrological model results. WF and JRY contributed to the global water quality model development. All authors contributed to the manuscript.

Supplementary data

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  • Published: 31 July 2019

Reassessing the projections of the World Water Development Report

  • Alberto Boretti   ORCID: orcid.org/0000-0002-3374-0238 1 , 2 &
  • Lorenzo Rosa   ORCID: orcid.org/0000-0002-9210-5680 3 , 4  

npj Clean Water volume  2 , Article number:  15 ( 2019 ) Cite this article

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The 2018 edition of the United Nations World Water Development Report stated that nearly 6 billion peoples will suffer from clean water scarcity by 2050. This is the result of increasing demand for water, reduction of water resources, and increasing pollution of water, driven by dramatic population and economic growth. It is suggested that this number may be an underestimation, and scarcity of clean water by 2050 may be worse as the effects of the three drivers of water scarcity, as well as of unequal growth, accessibility and needs, are underrated. While the report promotes the spontaneous adoption of nature-based-solutions within an unconstrained population and economic expansion, there is an urgent need to regulate demography and economy, while enforcing clear rules to limit pollution, preserve aquifers and save water, equally applying everywhere. The aim of this paper is to highlight the inter-linkage in between population and economic growth and water demand, resources and pollution, that ultimately drive water scarcity, and the relevance of these aspects in local, rather than global, perspective, with a view to stimulating debate.

Introduction

The 2018 edition of the United Nations (UN) World Water Development Report (WWDR) 1 has provided an update on the present trends of clean water availability and future expectations. Water security, the capacity of a population to safeguard sustainable access to adequate quantities of water of acceptable quality, is already at risk for many, and the situation will become worse in the next few decades. 2 Clean water scarcity is a major issue in today’s’ world of 7.7 billion people. The strain on the water system will grow by 2050 when the world population will reach between 9.4 and 10.2 billion, a 22 to 34% increase. The strain will be aggravated by unequal population growth in different areas unrelated to local resources. Most of this population growth is expected in developing countries, first in Africa, and then in Asia, where scarcity of clean water is already a major issue.

At present, slightly less than one half of the global population, 3.6 billion people or 47%, live in areas that suffer water scarcity at least 1 month each year. 1 According to, 3 the number is even larger, 4.0 billion people, or 52% of the global population. By 2050, more than half of the global population (57%) will live in areas that suffer water scarcity at least one month each year. 1 This estimate by 1 may be an underestimation. The water demand, water resources, and water quality forecast by 1 depends on many geopolitical factors that are difficult to predict. The decline of water resources and water quality only partially discussed in, 1 may be much harder to control.

The WWDR 1 focuses on the application of nature-based-solutions (NBS), measures inspired by nature such as the adoption of dry toilets, which will have a negligible effect on the huge problem. More concrete regulatory measures are needed to tackle the clean water crisis, directly acting on water use and conservation. There are major obstacles to providing adequate water planning. First is the refusal to admit that unbounded growth is unsustainable. 4 Overpopulation arguments are portrayed as “anti-poor”, “anti-developing country” and “anti-human”. 4 Population size as a fundamental driver of scarcity is dubbed as a “faulty notion”. 5 This denial is partly responsible for lack of good water planning, supported by overconfidence in NBS. The key points of the WWDR 1 are summarized and discussed in the following sections.

Water demand by 2050

Increasing water demand follows population growth, economic development and changing consumption patterns. 1 Global water demand has increased by 600% over the past 100 years. 5 This corresponds to an annual increment rate of 1.8%. According to, 6 the present annual growth rate is less, only 1%, but this figure may be optimistic. Global water demand will grow significantly over the next two decades in all the three components, industry, domestic and agriculture. 1 Industrial and domestic demand will grow faster than agricultural demand but demand for agriculture will remain the largest. 1 The growth in non-agricultural demand will exceed the growth in agricultural demand. 7

Global water demand for all uses, presently about 4,600 km 3 per year, will increase by 20% to 30% by 2050, up to 5,500 to 6,000 km 3 per year. 2 Global water demand for agriculture will increase by 60% by 2025. 8 By 2050 the global population will increase to between 9.4 to 10.2 billion people, an increment of 22% to 32%. 1 Most of the population growth will occur in Africa, +1.3 billion, or +108% of the present value, and Asia, +0.75 billion, or +18% of the present value. 9 Two-thirds of the world population will live in cities. 1 These estimates of future population and water demand are the best we have, though it is realized such forecasts are difficult. 5

Globally, water use for agriculture presently accounts for 70% of the total. Most are used for irrigation. Global estimates and projections are uncertain. 1 The food demand by 2050 will increase by 60%, 1 and this increment will require more arable land and intensification of production. This will translate into increased use of water. 10 Global use of water for industry presently accounts for 20% of the total. Energy production accounts for 75% of the industry total and manufacturing the remaining 25%. 11 Water demand for the industry by 2050 will increase everywhere around the world, with the possible exceptions of North America and Western Europe. 5 Water demand for the industry will increase by 800% in Africa, where present industry use is negligible. Water demand for the industry will increase by 250% in Asia. Global water demand for manufacturing will increase by 400%.

Global water use for energy will increase 20% over the period 2010–2035, 5 and by 2050 will increase by 85%. 12 Domestic global water use currently accounts for 10% of the total. Domestic water demand is expected to increase significantly over the period 2010–2050 in all the world regions except for Western Europe. The greatest increment, 300%, will occur in Africa and Asia. The increase will be 200% in Central and South America. 5 This growth is attributed to the increase in water supply services to urban settlements. 5

Clearly, the demand for water by 2050 will increase dramatically, but unequally, across all the continents. Quantitative estimates are difficult to provide with accuracy. The estimates of the WWDR 1 are not expected to be very accurate, and likely optimistic.

Water resources by 2050

Water demand cannot exceed water availability. While water demand is increasing, water availability is shrinking, because of shrinking resources and, as discussed in the next paragraph, pollution. The available surface water resources are forecast to remain about constant at continental level, 5 although quality will deteriorate, and spatial and temporal distribution will change. More likely, aquifers will shrink, and salt intrusion in coastal areas will be very dramatic. In contrast, the growth of population, gross domestic product (GDP), and water demand will increase globally and unequally. 5 Changes will be much more pronounced at the sub-regional level than at the country level, and the global average. 5

Many countries are already experiencing water scarcity conditions. 13 Many more countries will face a reduced availability of surface water resources by 2050. 13 In the early to mid-2010s, 1.9 billion people, or 27% of the global population, lived in potential severely water-scarce areas. 1 In 2050, this number will increase 42 to 95%, or 2.7 to 3.2 billion peoples. 1 If monthly, rather than annual, variability is considered, 3.6 billion people worldwide, slightly less than 50% of the global population, presently live in potential water-scarce areas at least 1 month per year. This number will increase from 33 to 58% to 4.8 to 5.7 billion by 2050. 13 About 73% of the people affected by water scarcity presently live in Asia. 1

In the 2010s, groundwater use globally amounted to 800 km 3 per year. 5 India, the United States, China, Iran, and Pakistan accounted for 67% of the global extractions. 5 Water withdrawals for irrigation are the primary driver of groundwater depletion worldwide. The increment of groundwater extractions by 2050 will be 1,100 km 3 per year, or 39%. 5 Improving the efficiency of irrigation water use may lead to an overall intensification of water depletion at the basin level. 14 At about 4,600 km 3 per year, current global withdrawals are already near maximum sustainable levels. 15

More than 30% of the world largest groundwater systems are now in distress. 16 The largest groundwater basins are being rapidly depleted. In many places, there is no accurate knowledge about how much water remains in these basins 17 and. 18 People are consuming groundwater quickly without knowing when it will run out, 17 and. 18 According to, 19 the world’s supply of fresh water may be much more limited than what is thought because unlimited groundwater was assumed. Challenges more severe than global are expected at regional and local scales. 16

Coastal zones have special problems. They are more densely populated than the hinterland, and they exhibit higher population growth rates and urbanization. Water withdrawal is already causing significant land subsidence, that combined to thermo-steric sea level rise, translate in relative sea level rise in coastal areas and salinization of aquifers, 20 , 21 , 22 , 23 Water withdrawal-induced subsidence is reported in many coastal areas of the world, from North America, 24 , 25 , 26 to East Asia, 27 , 28 , 29 , 30 , 31 Population growth rates and urbanization in coastal areas are expected to further increase in the future, 32 , 33 Thermo-steric and land subsidence driven relative sea level rise will also reduce arable lands along the coast and within estuaries, 29 , 30 and reshape coastal regions. Especially coastal regions, which are home to a large and growing share of the global population, are undergoing an environmental decline 33 impacting water availability. The neglected dramatic changes of coastal areas, due to relative sea level rise by land subsidence and thermo-steric effects, that directly and indirectly affect water availability, are missing points in the WWDR. 1

Coral islands are a special case, however affecting a small share of the global population, as they depend on a lens of groundwater for their water supply. Overuse of water causes shrinkage of the groundwater lens, which eventually leads to saltwater intrusion. Increasing population also leads to more contamination of the groundwater, so many islands are suffering a reduction in water resources as well as increasing pollution.

Apart from the discovery of new aquifers, desalination is the most effective measure to increase water resources. However, it is expensive, and it requires significant energy inputs. Currently, about 1% of the world’s population living in coastal areas is dependent on desalination. The progress of desalination to 2050 is hard to predict, depending on economic and energetic energy issues.

The simple message is that water resources will decrease dramatically by 2050. Likely, the estimates of the WWDR 1 are not very accurate, and probably optimistic.

Water quality by 2050

The problem of water pollution is a weak part of the WWDR. 1 Pollution is becoming worse, especially in the last few decades, but seems to be inadequately reported. Pollution of water is correlated with population density and economic growth. 34 At present 12% of the world population drinks water from unimproved and unsafe sources. 34 More than 30% of the world population, or 2.4 billion people, lives without any form of sanitation. 34 Lack of sanitation contributes to water pollution. 90% of sewage in developing countries is discharged into the water untreated. 35 Every year 730 million tons of sewage and other effluents are discharged into the water. 36 Industry discharges 300 to 400 megatons of waste into the water every year.

Non-point source pollution from agriculture and urban areas and industry point source pollution contribute to the pollutant load. More than 30% of the global biodiversity has been lost because of the degradation of fresh-water ecosystems due to the pollution of water resources and aquatic ecosystems. 37 Wastewater recycling in agriculture, that is important for livelihoods also brings serious health risks. 1 Over the last 3 decades, water pollution has worsened, affecting almost every river in Africa, Asia and Latin America. 38

Water pollution will intensify over the next few decades 39 and become a serious threat to sustainable development. 39 At present 80% of industrial and municipal wastewaters are released untreated. 40 Effluents from wastewater are projected to increase because of rapid urbanization and the high cost of wastewater treatment. 41 Nutrient loading is the most dangerous water quality threat, often associated with pathogen loading. 38 Agriculture is the predominant source of nitrogen and a significant source of phosphorus. 38 Current levels of nitrogen and phosphorus pollution from agriculture may already exceed the globally sustainable limits. 42 Global fertilizer use is projected to increase from around 90 million tons in 2000 43 to more than 150 million tons by 2050. 44 Intensified biofuel production will lead to high nitrogen fertilizer consumption. 43 Nitrogen and phosphorus effluents by 2050 will increase by 180 % and 150 % respectively. 45 Other chemicals also impact on water quality. Global chemicals used for agriculture currently amount to 2 million tons per year, with herbicides 47.5%, insecticides 29.5%, fungicides 17.5% and other chemicals 5.5%. 46

The list of contaminants of concern is increasing, 47 as a novel or varied contaminants are used, often suddenly detected at concentrations much higher than expected. 47 Novel contaminants include pharmaceuticals, hormones, industrial chemicals, personal care products, flame retardants, detergents, perfluorinated compounds, caffeine, fragrances, cyanotoxins, nanomaterials and cleaning agents. 47 Exposure to pollutants will increase dramatically in low-income and lower-middle income countries. 38 Pollution will be driven by higher population and economic growth in these countries, 38 and the lack of wastewater treatment. 40 Pollution will be particularly strong in Africa. 38

In brief, the demand for water will increase by 2050 but the availability of water will be reduced. Water resources will reduce. Pollution will further reduce the amount of clean fresh water. This aspect is marginally factored in the WWDR. 1

Other ecological changes by 2050

Changes in the ecosystems will be affected by changes in the water demand and availability and vice versa. Conservation or restoration of the ecosystems will impact on water availability for human consumption, both resources, and quality. 1 About 30% of the global land area is forested, and 65% of this area is already in a degraded state. 48 Grasslands and areas with trees, but dominated by grass, presently exceed the area of forests. Large areas of forests and wetlands have been converted into grasslands, for livestock grazing or production of crops. Wetlands only cover 2.6% of the land but play a significant role in hydrology. 49

The loss of natural wetland area has been 87% since 1700. The rate of wetland loss has been 370% faster during the 20 th and early 21st centuries. 49 Since 1900 there has been a loss of 64% to 71% of wetlands. 49 Losses have been larger, and are now faster, for inland, rather than coastal, wetlands. 49 The rate of loss is presently highest in Asia. The effects of sea level rise are underrated in. 49

Soils are also changing. Most of the world’s soils are in only fair, poor or very poor condition, 50 and the situation is expected to worsen in the future. 50 The major global issues are soil erosion, loss of soil organic carbon and nutrient imbalance. Presently, soil erosion from croplands carries away 25 to 40 billion tons of soil every year. Crop yields and soil’s ability to regulate water, carbon, and nutrients are reduced. 23 to 42 million tons of nitrogen and 15 to 26 million tons of phosphorus are presently transported off the land. Soil erosion and nutrient run-off have negative effects on water quality. 50 Sodicity and salinity of the soils are global issues in both irrigated and non-irrigated areas. Sodicity and salinity take out 0.3 to 1.5 million ha of farmland each year. 50 The production potential is also reduced by 20 to 46 million ha. 50

Ecosystems, biodiversity, and soil degradation are expected to continue to 2050, at an ever-faster rate. This will have an impact on the availability and quality of water, which is only partially considered in the WWDR. 1

The data presented in, 1 provide an optimistic, but still dramatic, estimation of water scarcity by 2050. Their gentle, nature-based-solutions (NBS) are quite inadequate to tackle this serious problem. Limitation of population and economic growth cannot be enforced easily. Ad hoc responses seem to be necessary but hard to be implemented.

Figure 1 presents in (a) the global water withdrawal, the GPD pro-capita and the world population since the year 1900, and in (b) the population of the world and of selected countries of Asia and Africa since the year 1950. The figure also presents in (c) the graphical concept of water scarcity, resulting from a more than linear growing demand, and a similarly more than linear reducing availability of clean water. It is intuitive that growing demand and shrinking availability will ultimately cross each other, locally earlier than globally.

figure 1

a Water withdrawal, GDP pro-capita, and world population. The water withdrawal data to 2014 is from. 71 The GPD pro-capita data to 2016 is from. 73 The population data to 2018 is from. 72 b The population of the world and selected countries of Asia and Africa. The data to 2018 is from ref. 72 The values for 2050 are obtained by linear extrapolations from recent years. c Graphical concept of water scarcity, resulting from a more than linear growing demand and a similarly more than a linear reduction of clean water availability

Demand for water, same of food or energy, increases with the growth of population and gross domestic product (GDP) pro-capita. 51 In addition to the growth of population, also the generation of wealth worldwide translates in increased consumption, resulting in increased water demand. The expected changes in wealth are coupled to alterations in the consumption patterns, including changes to diet. As agriculture worldwide accounts for up to 70% of the total consumption of water, 52 , 53 , 54 , 55 with much higher levels in arid and semi-arid regions, food and water demands are on a collision path. One example of conflicting demands for water, food, and energy, within a context of regional population and economic growth, is the Mekong Delta. The morphology of the Mekong Delta as we know today developed in between 5.5 and 3.5 ka (thousand years before present). The relatively stable configuration experienced during the last 3.5 ka has been dramatically undermined during the last few decades. The delta itself may completely disappear in less than one century.

The increased demand for food, water, and energy of a growing population and a growing economy has translated in the extraction of larger quantities of groundwater in the delta, the construction of hydroelectric dams along the course of the river, the diverted water flow for increased upstream water uses, and the riverbed mining for sand. The reduced flow of water and sediments to the delta, 56 , 57 , 58 , 59 , 60 coupled to the subsidence from excessive groundwater withdrawal and soil compaction, 58 , 61 , 62 , 63 , 64 , 65 and the thermo-steric sea level rise, 66 , 68 , 74 have translated in the sinking and shrinking of the delta. In the short term, this has translated in salinization of coastal aquifers, depletion of aquifers, and arsenic pollution of deep groundwater, additional to salinization of soil, flooding, destruction of rice harvesting and depletion of wild fish stocks, impacting on water and food availability, 67 , 68 In the longer term, the delta itself may completely disappear as the result of not sustainable growth. 69 , 70

As previously mentioned, apart from the discovery of new aquifers, increased use of desalination and water purification may lessen the reduction of available water. However, desalination needs significant economic and energetic energy input, difficult to predict. The water withdrawal data is obtained from. 71 The population data is obtained from. 72 The GPD pro-capita data is obtained from. 73 The values by 2050 are obtained by linear extrapolations. The global water withdrawal is correlated to the world population, but it has been growing faster than the world population. The GPD pro-capita has been growing even faster than the world population. While we do not have any reliable data on water quality and resources vs. time, over the same time window, we expect that the water quality and resources have also been deteriorating more than proportionally to the economic and population growth.

Use of fertilizers has grown even faster than the global water withdrawal. 74 Production and consumption of nitrogen, phosphate and potash fertilizers since 1961 has similar growing patterns. 75 Global pesticide production is also growing continuously. 76 The key driver for pollution is the growth of the population and the economy. 41 The groundwater basins are being quickly exhausted by excessive withdrawals. Additionally, because of the relative sea level rise, thermo-steric and groundwater withdrawal generated subsidence, aquifers in coastal lands and estuaries are being rapidly compromised, while fertile lands are turned unproductive, 29 , 30 Similarly, to water demand, also water resources and water quality are thus linked to economic and demographic growths. Opposite to the population and GDP data, the data of fresh water usage, fresh-water resources, and pollution of fresh water, are more difficult to be sorted out with the accuracy needed, making every forecast to 2050 problematic.

Regarding the economy, it must be added that the IMF’s Global Debt Database 77 indicates that the debt has reached globally in 2017 an all-time high of $184 trillion, or 225% of the GDP. The world’s debt now exceeds $86,000 per capita, which is more than 250% of the average income per capita. The most indebted economies in the world are the richer ones, with the United States, China, and Japan accounting for more than half of the global debt, and the poorer countries on their way to becoming indebted.

The three key aspects of water scarcity, water demand, water resources, water pollution, are strongly related to population growth and economic growth. They are strongly interconnected, and dramatically variable in space and time, with local conditions that will be much worse than the global conditions. Many countries are experiencing population growth largely exceeding the already alarming global average. Linear extrapolations to 2050 are in some cases in excess, and in some cases in defect, of the values forecast in, 72 demonstrating complex dynamics. For example, the population forecast to 2050 for Uganda is 105,698,201, or +2,110% vs. the values of 1950. The linear extrapolation to 2050 is 89,313,923, or +1,783% vs. the values of 1950. Opposite, the population forecast to 2050 for the world is, optimistically, 9,771,822,753, or +385% vs. the values of 1950. The linear extrapolation to 2050 is 10,274,650,493, or +405% vs. the values of 1950. Global growths of 385 to 405% over 100 years are everything but sustainable. Even less sustainable are local growths that at the country level are exceeding 2,000% over 100 years. It is impossible to provide clean fresh water to support such growth rates.

As clean water demand is increasing, and clean water availability is reducing, with local situations much worse than global, clean water demand will eventually exceed the availability of clean water at some local levels much earlier than at the global level. These break-points may occur earlier than 2050 in many areas of the world. Considering when a vital resource is in short supply, people will fight for it, provision of water to 2050 will be very likely played against a social background of competition and probably conflict if nothing will be done to prevent a water crisis.

Conclusions

The paper has discussed the correlation between the exponential growth in global population and GDP and water scarcity, that is the result of the competing water demand, water resources, and water pollution. Population and economic growth to 2050 will be very likely strong, and unequal across the globe, with the largest growth rates expected in third world countries. Water demand to 2050 will grow even more than the population and the economy, same of the reduction of water quality and resources. Local patterns will be more critical than global patterns, making the problem more difficult to be solved.

Water is ultimately a finite resource and the marginal solutions for water scarcity currently being proposed in the United Nations (UN) World Water Development Report (WWDR) will prove hopelessly inadequate by 2050 in the absence of any serious effort to tackle these underlying truths. Improvements in the science and technology of water treatment, water management and clean water supply, and in the awareness of water conservation and savings, while developing nature-based-solutions (NBS), may certainly alleviate future clean water scarcity. However, a better policy is much more urgent than scientific, technological and philosophical advances, as this will not be enough. There is a clear regulatory promulgation and enforcement issue especially in the developing countries that needs to be addressed the sooner the better. We need the political will to enforce global regulations, especially where economies and population are building up, as unregulated development is not sustainable anymore.

There is no specific remedial measure to propose, if not to support more sustainable population and economic growths, with local rather than global focus, keeping in mind that growth cannot be infinite in a finite world. As the Economist Kenneth Boulding declared to the United States Congress 78 “Anyone who believes exponential growth can go on forever in a finite world is either a madman or an economist”. However, as noted in, 79 the pursuit of economic growth has been the prevalent policy goal across the world for the past 70 years. The aim of this paper is simply to highlight the connection between population and economic growth and water demand, resources and pollution, that ultimately drive water scarcity, and the relevance of these aspects in local, more than global perspective, to stimulate an urgent and comprehensive debate.

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research paper on scarcity of water

Assessment of water scarcity and its impacts on sustainable development in Awash basin, Ethiopia

  • Original Article
  • Published: 12 May 2015
  • Volume 1 , pages 71–87, ( 2015 )
  • Dereje Adeba   ORCID: orcid.org/0000-0003-3129-6871 1 ,
  • M. L. Kansal 1 &
  • Sumit Sen 2  

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Equitable access and rational use of water resources is important to cope with water scarcity. The optimal allocation of limited water resources for various purposes is required for sustainable development. Awash river basin is one of the most utilized river basins in Ethiopia. There is increasing demand for water due to recent population growth in the basin because of Urbanization. Excessive water abstraction without properly assessing the available water resources in the basin contributes to water scarcity. The basin exhibits two extreme hydrological events, flooding and drought at different seasons of the year. This paper mainly focuses on surface water resources assessment of the Awash basin, and the temporal gap between water supply and demand. The paper also discusses the impacts of these gaps on sustainable development and suggested few recommendations to minimize it. Using SWAT model, the annual average surface water available is estimated around 4.64 Billion Cubic Meters (BCM) as compared to the estimated demand of about 4.67 BCM in the basin for 1980–2012. This shows that on an average, the demand exceeds the availability by 0.03 BCM during the study period. Seasonal water deficit is even serious. A detailed seasonal analysis for the last 2 years (2011–2012) shows that the demand exceeds supply by 1.27 and 2.82 BCM during December–April of 2011 and 2012, respectively. However, there is a surplus supply of 1.67 and 3.16 BCM during June–September months of the same year.

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Introduction

Geographically, Ethiopia is located between 3° to 18°N latitude and 33° to 48°E longitude. The total land mass of the country is about 1.13 million square Kilometre, and the current population is estimated at 93 million. Figure  1 shows the location map of Ethiopia in the horn of Africa.

Location map of Ethiopia

Water resource development is essential to bring about sustainable growth of agriculture, rural development and overall economic progress. Equitable access and sustainable water resources development in a participatory approach of all stakeholders is important to cope with water scarcity. The management and delivery of services in this regard should be to promote the integrated water resources management in a river basin for economic welfare of the people without compromising sustainability of environmental health. The optimal allocation of limited water resources for various purposes is important. There are 12 river basins in Ethiopia. Out of these, two are dry, two are water surplus and eight of them are water deficit basins of different levels. The total runoff from these basins was estimated around 122 BCM per year (Ethiopian River basin master plan studies). There is always some problem related to water in dry and deficit basins which impacted the livelihood of the community and the development activities. The Awash river basin is one of the river basins of Ethiopia located between 7°53′N and 12° latitude and 37° 57′E and 43°25′ longitude. It rises at an altitude of about 3000 ma.m.s.l to the west of Addis Ababa, the capital city of the country. Then it flows to the easterly direction and ends at Abbe Lake, the international border of Ethiopia with Djibouti. The river is about 1250-km long. Awash river basin is the most utilized and polluted river basin. The big cities which are located in this basin are dependent on the water of the basin for different purposes. As for water supply, all of Addis Ababa’s domestic water sources are reservoirs which are located in rural landscapes of the basin. Water is supplied from three reservoirs (80 %) and one groundwater system (20 %) with a total volume of 210,000 m 3  day −1 or 0.0767 Billion Cubic Meters (BCM) per year (Van Rooijen and Tadesse 2009 ). There is an increasing water demand due to recent population growth because of urbanization. On the other hand, there is obvious reduction in water availability in time and space due to both natural and anthropogenic causes. Water is wasted in all sectors, because it is provided by public systems at little or no costs to the users (Kansal et al. 2014 ). No one in the allocation system shows an interest to conserve water. The price of water is heavily subsidised and does not cover the cost of delivery. The role of water price in water distribution system is that it helps in efficient allocation of existing water supplies. It helps adjust demand to the available supply and in equitable treatment of water users. Effective pricing structure helps achieving in conservation of water by reducing peak demands on the system. Prices charged can also affect quantity of water withdrawn by commercial and industrial users, thereby affecting the volume of water that returns through sanitary sewers for treatment. The real cost of water (development, transport, treatment and delivery) must be reflected in water rates when prices are fixed.

Irrigation potential is very high in the basin. The estimated land area suitable for irrigation is about 205,400 ha, 4.7 % of irrigable area in the country (Taddese et al. 2012 ). Many of the commercial farms in the country are located along the middle and downstream of the basin, and large-scale withdrawals of water in this basin are for irrigation purpose. The nature and water yielding process of every basin are unique, and water abstraction should be done with the basic understanding of the complex nature of the basin. In some of small- and medium-scale irrigation projects, water is available to users at no cost or at a heavily subsidised price. The current situation of the basin therefore reflects a water crisis by the general mismanagement and over exploitation of water resources. Irrigation efficiency is low and it is time to introduce current technologies, such as drip, sprinkler and canal irrigations which can save water without decreasing productivity of the system. Implementation of such technologies will enhance the potential of the Awash river to sustainably serve the basin communities.

Policies should be designed to avoid mismanagement and overuse of water in different sectors. Strict rationing is often required to allocate the resulting scarcity so that a large share of water to meet demand must come from water saved from different uses through water policy reform. Demand management can bring about physical savings of water by improving the efficiency of water use especially in agriculture (FAO 2012 ). Efficiency in water use should also improve in urban and industrial uses. Supply management can be another option to address the problem of water scarcity in the basin.

Water pollution in the basin is another basic problem which aggravates water shortage. The industries in the major cities of Ethiopia located in the basin are the sources of water pollution. Urbanization, industrial development agricultural chemicals and fertilizers overcharged the carrying capacity of water bodies and resulted in deterioration of surface water quality and groundwater aquifer in the basin. Pollutants such as toxic metals from the tanneries are the main sources of pollution. Sugarcane base industry is another source of pollution to the basin due to large quantity of wastewater having high pollutant concentration. These effluents discharged into the river either without treatment or with minimum treatment. This issue requires an urgent attention from the government and stakeholders. Water logging and salinization are putting increasing pressure on land and water quality in the basin in irrigated agriculture.

Through collection and analysis of reliable and adequate data on water resource status, sound decisions can be made on how best to develop and manage these resources. Proper assessment of the water resources in time and space is important to plan future water use rationally and on a sustainable basis. The assessment of the availability of water in the basin and priority setting of its use is important before planning for the expansion and development of additional sectors which poses pressure on water availability. Therefore, the main objectives of this study are to (1) assess the total surface water availability, water demand and the gap between supply and demand in the basin and (2) recommend different options to minimize the gap between supply and demand.

Methodology

In order to achieve the above objectives, the methodology followed in this study includes the assessment of water resources availability and water demand.

Assessment of water resources availability

Water resources availability was estimated using Soil and Water Assessment Tool (SWAT) model. SWAT is a physically based continuous-time, long-term simulation, lumped parameter deterministic model developed by United States Department of Agriculture-Agricultural Research Service (USDA-ARS), Arnold and Fohrer ( 2005 ); (Gassman et al. 2007 ). It is not designed to simulate detailed, single-event flood routing (Neitsh et al. 2002 ). It operates on a daily and hourly time steps. The model is computationally efficient and it uses physically based inputs like weather variables, soil properties, topography, vegetation and land management (Singh et al. 2013 ). The basin boundary and the drainage pattern of the basin are delineated by ArcGIS10.1 with a 90-m-resolution digital elevation model.

The conceptual framework of the model developed in this research shows the database types and its linkage to different points in the process of SWAT model. The spatial and hydro-meteorological data were used for initial setup of the Model (Fig.  2 ). The climatic data used by the model can be a measured data or it can be generated by the model using in-built weather generator. However, for this study, only measured data were used. The location tables of different weather data were loaded and linked to the files created for this purpose to write input tables by the model. During the writing-up process of input tables, additional data like Manning’s roughness coefficient for overland flow, soil data, hydrologic data and management inputs were set up for simulation of the model. When Penman–Monteith or Priestly-Taylor (Monteith 1965 ) evapo-transpiration routines are used, the SWAT model requires relative humidity, solar radiation and wind speed as an input data (Gassman et al. 2007 ). In case the Green-Ampts infiltration method is used, the measured or generated sub-daily precipitation inputs are required as the input to the model (Gassman et al. 2007 ). The maximum and minimum temperature inputs are used in the calculation of daily soil and water temperature (Gassman et al. 2007 ). Finally, the model was set up to simulate the various hydrological components of the basin.

Conceptual framework of SWAT model and its set up

Though, three options exist in SWAT for estimating surface runoff from HRUs, and the USDA Natural Resources Conservation Service (NRCS) curve number (CN) method is used to estimate surface runoff in this study.

Soil and Water Assessment Tool estimates surface runoff using SCS-CN method,

where Q  = runoff depth in mm, P  = effective rainfall in mm, I a  = Initial abstraction in mm and S  = potential maximum retention. But, the initial abstraction, I a is the function of potential maximum retention S . Therefore,

where λ  = 0.2 Therefore,

Substituting Eq.  2 in 1 we have,

Runoff occurs when P is greater than 0.2S. The potential retention parameter varies based on type of soil, land use management and slope of the watershed. The potential maximum retention S is related to the dimensionless parameter CN by the following relation:

where CN = curve number.

The output of SWAT model includes surface runoff, evapo-transpiration, stream flow, interception storage, infiltration, reservoir water balance and shallow and deep aquifer that have been developed and validated. The interest of this study is only the surface water availability of the basin. So the outflow of the basin from each subbasin is added to get the total surface water availability.

The uncertainty of parameters such as measured data uncertainty, model uncertainty and parameter uncertainty was checked by using sequential uncertainty fitting (SUFI2). The goodness of fit and the degree to which the calibrated model accounts for the uncertainties are assessed by running p -factor and r -factors test which were explained in the ‘sensitivity analysis’ section.

Water demand assessment

In Awash basin, satisfying water demand for agricultural production is an integral part of food self sufficiency and employment opportunity for the community living in the basin, because agriculture is the foundation of the economy and it employs more than 80 % of the rural population in the country. To calculate the water balance of the basin, the demand of water for different uses is required. To know the demand, it is necessary to assess the human population, livestock population, irrigation activities in the basin and industrial firms available in the basin. After calculating the demands of water for each sector including environmental water requirement, it is added together to arrive at the total water demand and then it is subtracted from the availability of water in the basin to get the balance.

Model performance evaluation criteria

The accuracy of SWAT simulation results is determined by examination of the coefficient of determination ( R 2 ), the Nash and Sutcliffe ( 1970 ) model efficiency coefficient (NSE), the root mean square error (RMSE), percentage bias (PBAIS) and observation standard deviation ratio (RSR). The R 2 value is an indicator of the strength of the linear relationship between the observed and simulated values, while the (NSE) simulation coefficient indicates how well the plot of observed versus simulated values fits the 1:1 line. The R 2 statistic is calculated as

where R 2  = Coefficient of determination, O i  = Observed (measured) value and P i  = Modelled (predicted) value.

The SWAT model is further calibrated monthly using the NSE, which is given as,

The root mean square error and mean absolute error are well-accepted absolute error goodness-of-fit indicators that describe differences in observed and predicted values (Legates and McCabe 1999 ). It is calculated using the relation,

Percent bias (PBIAS) measures the average tendency of the simulated data to be larger or smaller than their observed counterparts (Gupta et al. 1999 ). The optimal value of PBIAS is 0.0, with low magnitude values indicating accurate model simulation (Moriasi et al. 2007 ). Positive values indicate model underestimation bias, and negative values indicate model overestimation bias (Gupta et al. 1999 ).

PBIAS is calculated by

Observation standard deviation ratio (RSR) standardizes RMSE using the observations standard deviations and it combines both an error index and the additional information recommended by (Legates and McCabe 1999 ). RSR is calculated as the ratio of the RMSE and standard deviation of measured data, as given:

Data requirement and availability

Assessment of a basin water balance is vital to understand the processes of hydrologic cycle. For this purpose, data collection and field trip for ground truthing, and data verification were used to identify the key features of the basin. The hydrological and meteorological data from 1980 to 2012 were supplied by the Ministry of Water Resources (MoWR) and National Meteorological Service Agency (NMSA) of the government of Ethiopia, respectively. Quality of meteorological data was checked by comparing graphs and double mass curve analysis. The missing data were filled using regression method (Hassan and Croke 2013 ). River basin master plan study document of the Awash river is consulted, Water Works Design and Supervision Enterprise (WWDSE)/WAPCOS ( 2005 ). Information on water abstraction for different purposes was also gathered from different sources, such as water allocation study of the upper Awash valley for existing and future demands (Berhanu 2008 ; Yibeltal et al. 2013 ).

Digital elevation models (DEMs) are used to identify stream networks and the land slopes that contribute flow to the water bodies. Modelling of the hydrologic responses over a watershed requires use of soil map and land use/land cover map to provide information on soil types and their hydrologic properties.

The soil physical properties like soil texture, available water content, hydraulic conductivity, bulk density and organic matter content for different layer were processed using Soil–Plant-Air–Water (SPAW) software developed by United States Department of Agriculture (Table  1 ). The land use of the basin is analysed to check for a significant land use change for the period of 2008–2012. However, there was no significant change during this period, and thus, 2012 land use data were used.

Study area description

Awash basin covers the total land mass of 110,000 km 2 out of which 64,000 km 2 is categorized as western basin and contributes almost the entire surface flow of the basin. Other 46,000 km 2 area comes under the eastern part which does not contribute any surface flow to the river (MoWR 2014 ). The elevation of the basin ranges between 250 m at the Abbe Lake, where the river ends and 4195 ma.m.s.l at the headwater of the river (Fig.  3 ). The basin is divided into upper, middle and lower Awash. The annual rainfall of the basin varies from about 160 mm at the northern limit of the basin to 1600 mm in the western highlands. The mean annual rainfall of the basin is about 895 mm. Mean annual temperature ranges from 9.9 °C at the North West to 30.5 °C at the north east of the basin. During the simulation period (1980–2012), the lowest and the highest temperatures recorded in the basin were 0 and 36 °C, respectively at different locations. The rainfall and the maximum and minimum temperatures of the basin at different stations are shown in (Fig.  4 ). The average wind speed during the same period was 2.7 m/s and the maximum value recorded was 9.9 m/sec, while the average relative humidity was 55.35 %. The physical properties of soil control the movement of water through its profile and impacts on the cycling of water within HRU. Based on physical properties, soil of the basin was classified into 17 different classes and indicated in (Fig.  5 ) below. Slope of the basin is manually divided into three classes (Table  2 ).

Location map of Awash basin

Long-term weather data of Awash basin at different stations

Soil map of Awash basin

Agriculture is the dominant land use in the basin followed by grassland and shrub land with 51.39, 29.79 and 8.11 %, respectively, as shown in (Fig.  6 ).

Land use map and slope classes of Awash basin

Rainfall, Maximum and Minimum temperature data of the basin for the last 33 years (1980–2012) are shown in the following figure.

Results and discussion

Sensitivity analysis.

Sensitivity analysis is one of the necessary phases in model calibration and preparation for use. It is used to determine the way the results are changing based on change of model parameters. Sensitivity analysis was conducted to identify the sensitive parameters affecting stream flow for subsequent application in stream flow calibration (Kannan et al. 2007 ). It was carried out using those parameters provided in the SWAT literature (Table  3 ). The values of the parameters used for sensitivity analysis were within the range suggested in SWAT user’s manual and literature (Neitsh et al. 2001 ).

p -factor is used to quantify the degree to which all uncertainties are accounted for and it is the percentage of measured data bracketed by the 95 % prediction uncertainty, (Abbaspour 2012 ) while r -factor quantifies the strength of calibration/uncertainty analysis i.e. r -factor is the average thickness of the 95ppu band divided by the standard deviation of the measured data. The value of p -factor ranges from 0 to 100 % while that of r-factor ranges between 0 and infinity. A p -factor of 1 and r -factor of 0 is a simulation that exactly corresponds to the measured data. The degree to which the simulated value deviates from these values of p and r can be used to judge the strength of model calibration.

Model calibration and validation

Models approximate the reality of the natural systems. Both graphical methods and statistical tests are used in model calibration and validation. The details of simulation of the basin are given in Table  4 . The model on the first level is manually calibrated because this is performed only once in the initial calibration phase (Milivojevic et al. 2009 ). Manual calibration supported by semi-automatic calibration using SUFI2 (Sequential Uncertainty Fitting 2) was used for model calibration and validation. The model has been calibrated and validated using observed stream flow time series for six gauging stations (Table  5 ). The result shows a good model performance for the basin (Fig.  7 ). During the calibration period (1980–1999), the Nash–Sutcliffe efficiency (NSE) for monthly flow simulations varied between 0.75 and 0.90, while the R 2 value for the same period of calibration varied between 0.78 and 0.92. But during the validation period (2000–2012), NSE values range from 0.55 to 0.93, while the value of R 2 ranges from 0.57 to 0.95 for the basin.

Calibration and validation of flow data of the basin at different stations

Model calibration parameters

AWC, CN2, APHA_BF, GW_DELAY, REVAP_MN, etc. are some of the parameters used for calibration (Table  6 ). An increase in AWC will decrease surface runoff and base flow and hence results in decreased water yield, i.e. AWC is inversely related to water balance components. Evaporation compensation factor (ESCO) also affects the water balance components. The observed and predicted flow values are closer when ESCO values are near its maximum for the basin. This is the results of an increased base flow value and surface runoff for high values of the soil evaporation compensation factor. This study shows that the water balance components for the Awash basin are least sensitive to GW_SPYLD values i.e. a change in the initial GW_SPYLD value will not greatly affect water balance components.

Estimation of water yield of the basin

Water scarcity in Awash basin is projected to increase over time due to increasing population, change in climate, land use and land cover. Water balance models such as SWAT can be used to assess the availability of water resources and the long-term influences of water management on the resources. This helps in planning mitigation measures against water scarcity that the future generation is inevitably going to face. The water yield of the basin when modelled by SWAT is the total amount of water generated by subbasin and entering the main channel system. It is the important parameter to be estimated for efficient management and planning. The water balance equation in its general form is given as inflow = outflow + change in storage. This equation can be applied for any size of basin and any period of time to evaluate all inflow, outflow and water storage component. For different HRUs, runoff is predicted separately and then routed to obtain total runoff for the subbasin. This enhances accuracy and gives a better description of water balance.

The contribution of each subbasin during the simulation period is summed up to arrive at the total yield of water by the basin. The water yield is in depth unit and it is multiplied by the area of the basin to get the volume of the water yield. A total of 4.64 BCM of water is estimated for the basin by the model.

  • Water demand

Domestic water demand

The domestic water demand is estimated based on the basin population and the minimum standard required per person per year. A range of estimates of per capita water requirements have been developed, ranging from 20 litres per capita per day (l/c/d) through to 4,654 l/c/d, (Jonathan 2000 ). Humans require fresh water for three broad uses. This include domestic use such as drinking, washing, food preparation and general hygiene, agricultural use in order to produce food, and industrial use for non-agricultural commercial activities. There are two approaches for estimating the minimum amount of water required to sustain a high level of human development (Jonathan 2000 ). Considering a minimum per capita water availability of 145 l/c/day for urban population and 45 l/c/day for rural population, the total domestic water requirement of the basin will be 0.326 BCM/year.

Irrigation water demand

The crop water need (ET crop) is the depth or the amount of water needed to meet the water loss through evapo-transpiration. It depends on climate (sunshine, temperature, humidity, and wind speed), crop type and the growth stage of the crop. The influence of the climate on crop water needs is given by the reference crop evapo-transpiration, ETO (FAO Water 2012 ). Due to time constraint to collect all relevant data required to estimate water requirement for irrigation, previous study results were adapted. Yibeltal et al. ( 2013 ) made a comprehensive irrigation assessment in the basin and found out that the agricultural water requirement of the basin is estimated at 2.52 BCM for 2012 cropping pattern.

Livestock water demand

Providing good quality water is essential for healthy livestock husbandry. The daily water requirement of livestock varies significantly among animal species (Table  7 ). The animal’s size and growth stage will have a strong influence on daily water intake. Consumption rates can also be affected by environmental and management factors. Feed with relatively high moisture content decreases the quantity of drinking water required (Taddese et al. 2001 ).

Industrial water requirement

Industries that produce metals, paper, pharmaceuticals, chemicals, liquor, textiles and others all use water in their production process. It depends on water for all levels of production. Data on industrial water use are difficult to get because most of them use their own water sources. Water for industry use is not registered by municipality. For Addis Ababa alone, the estimate of these data is obtained from the Addis Ababa water supply and sewerage agency. The estimate of water use for industries in and around Addis Ababa is about 8 % of the total daily domestic water requirement of the city. This is equivalent to approx. 16,800 m 3 /day and 0.00613 BCM/year for Addis Ababa and its surrounding. For industries outside Addis Ababa but located in the basin, it is assumed that their water requirement is about 0.001 % of the basin yield which is equivalent to 0.00464 BCM. Therefore, the total industrial water requirement in the basin is estimated at 0.01084 BCM.

Environmental water requirement

The specification of an environmental water requirement varies depending on the objective of environmental water management. It can be a complex and its estimation should be viewed in the context of natural variability of flow regimes (Poff et al. 1997 ). The most appropriate methodology depends on the individual case, including the specific objectives of the task, the amount of data and other available information. The total environmental water requirement consists of ecologically relevant low-flow and high-flow components (Smakhtin et al. 2004 ). There is seasonal flow variation in river basins depending on the rainfall. Up to 75 percent of the annual flow may come during rainy seasons in the basin. The river flows may reduce to a great extent during dry periods. It has been estimated that approximately 20–50 percent of the mean annual river flow in different basins needs to be allocated to freshwater-dependent ecosystems to maintain a fair condition (Smakhtin et al. 2004 ). For Awash basin, the environmental flow requirement is estimated to be about 35 percent of the mean annual river flow i.e. 1.64 BCM/year.

  • Water balance

Water scarcity occurs when demand for water exceeds supply, and it can occur at any level of supply and demand. The total annual surface water resources potential of Awash basin according to this study is estimated to be about 4.64 BCM. The average water demand in the basin is about 4.67 BCM. This shows on the average, the deficit of 0.03 BCM of water in the basin. The seasonal deficit (intra-annual shortage) of water is even more serious than inter annual deficit, because the precipitation falling on the land surface in the basin is highly variable in space and time, resulting in seasonal water surplus and shortage. June to September is the rainy months of the basin, during which availability of water exceeds demand. This has negative consequences on demand, because, it builds up water demand during the period. As a result, it leads to over-allocation of water which cannot be satisfied during lean season. Due to this hydrological variability and water management, water scarcity varies over time. The monthly deficit and surplus of water is shown in Fig.  8 . During December–April month of 2011, the basin shows a deficit of 1.27 BCM, while there is an excess water of 1.67 BCM during the months of May–November. In 2012, during the similar months, there is a deficit of 2.82 BCM, whereas there is a surplus of 3.16 BCM of water during June–November. The water scarcity in the basin is economic water scarcity (lack of water infrastructure, lack of investment in the sector, and lack of technical capacity) rather than physical water scarcity. The availability of water fluctuates from year to year and within a year. Therefore, if a storage structure is available, the surplus water can be stored for latter use and it can also serve the purpose of flood protection. In basins where water scarcity is a critical problem like in Awash basin, one of the options to control water supply to match demand is by providing storage reservoirs to capture floods during wet season. Storing water during the high-flow seasons and reallocating it during dry season can achieve potentially high benefits in the basin. It can reduce the gap between demand and supply to a large extent. Construction of high capacity dams to ensure yearly carryover capacity of close to 40 % of the annual river flow can help in achieving water security during lean season. Construction of large dams in the basin has an advantage of reliable yield because evaporation is relatively less due to their depth. The location of the reservoir needs to be carefully chosen near the service point to avoid conveyance losses. One of the options/or way forward is to have reservoirs in the west and southwest of the basin because it is in this part of the basin that maximum rainfall occurs and then huge runoff is generated. The temperature of this part of the basin is also relatively low indicating less evaporation loss.

Monthly surface water balance of Awash basin

In calculating the water demand, the domestic, industrial and livestock water demand is distributed uniformly over the year for convenience. The agricultural water demand is distributed over 5 months (December–April), because these months are critically dry months when the crops require water. Then demand versus supply graph is plotted. The graph is plotted yearly for the validation period from 2000 to 2012 (Fig.  9 ), and for the last 2 years (2011 and 2012), it is plotted on monthly basis to show the deficit clearly. The flow chart for surface water assessment and demand estimation to calculate surface water balance is shown in (Fig.  10 ).

Water balance for validation period (2000–2012)

Flow chart for water balance estimation

Agriculture is obviously the main water consumer. Irrigation efficiency in Ethiopia is low in the order of 30–40 percent (Yibeltal et al. 2013 ). A great deal of water can be saved by increasing the efficiency of irrigation and narrowing the gap between the stated policy and the actual practice regarding water resources management. The federal and/or regional level authorities should show an interest to enforce a law to keep control of an illegal abstraction of water. New small-scale irrigation schemes that are developed by individual farmers from time to time without planning can increase competition for water and thus create conflict between upstream and downstream users. So this expansion of small-scale irrigation should also be made on planning basis. The conflict between environment and agriculture in water demand, especially where almost total base flows are diverted for irrigation without releasing water for ecological conservation, should be examined and addressed.

Water can also be saved in industrial and urban water supply by rational use of water and recycling. Access to safe drinking water varies significantly among rural and urban areas. The water supply coverage for rural and urban is 41.2 and 78.8 % (Ministry of Water, Irrigation and Energy of the Government of Ethiopia 2010 ; Ministry of Water Irrigation and Energy Resources 2010 ), respectively. Large quantities of water can be saved by reducing leakages from pipelines, taps and storage tanks. It is estimated that approximately 40 % of domestic water supply is lost in distribution systems (Desalegn 2005 ).

Impacts of water scarcity on sustainable development

Water scarcity occurs as a result of climatic variability, increase in demand due to population growth which calls for increased allocation of water in the basin for different uses. Water poses a serious challenge to sustainable development. Its scarcity affects both social and economic sectors and threatens natural resources sustainability. Most of the communities living in the middle and downstream of the basin are pastoralists. Their livelihood entirely depends on animal husbandry. The availability of water is very crucial for these people and their animals. So they move from place to place in search of water and pasture specially during dry season. During drought which occurs frequently (once in every 5–10 years), they suffer a huge loss of animals and forced to depend on food aid from NGOs and Government. This usually impacted the country’s economy and constrained development.

Addressing water scarcity

Water is an important resource for socio-economic development, the livelihood of the community in the basin and ecosystem health. Therefore, the equitable and wise use of water is important to guarantee water security and address the conflict arising among communities. Irrigated agriculture is the major user of water in the basin. In order to have a sustainable growth in Ethiopia, irrigation sector must use water judiciously. Further, misuse and overuse of water in all the other sectors such as industrial, domestic, and public should be avoided, because water is a finite resource and its future supply is uncertain in the basin unless water saving measures are taken. Water saving requires attention because the current situation in the basin reveals that the freshwater supply is hampering sustainable economic development. Huge amount of water can be saved either from irrigation sector and/or domestic and industrial water supply by substituting obsolete irrigation technologies with modern ones like sprinkler and drip irrigation that have the potential to increase water use efficiency from 30–40 to more than 75 %. Metering of water helps in water demand management. A customer whose water is metered uses less water than those whose water is not metered because he knows that he must pay for any misuse.

Inter-sectoral and multidisciplinary approach in alleviating water scarcity ensures mutual understanding of the existing problem. This brings about coordinated action in management of scarce water resources of the basin to maximize socioeconomic growth on a sustainable basis. Water supply sources can be improved by water harvesting; improving water efficiency in agriculture, and reducing an unaccountable loss in domestic water supply. Water scarcity alleviation can also be achieved by increasing the productivity of water use in every sector. The restoration and conservation of watershed, that stores and releases water, is important to increase water availability.

Seasonal water scarcity in the basin can be overcome by capturing the rainwater which occurs during a short rainy season and causes flooding. Rain occurs in the basin during June–September and creates huge flood damage in the downstream region of Afar. Storing the runoff generated during this season has dual advantage for the country. The first and foremost advantage is that it protects the lives of thousands of people from flood damage at the downstream. The other advantage is that the stored water can be used for different purposes in dry season when the demand for water is high.

The policy issue of the country in water resources management and uses should be reconsidered. The policy should be designed to increase water efficiency, to improve water yielding processes of the basin and to discourage overuse of water by different sectors to address scarcity.

The issue of water pollution by industries and solid wastes needs immediate attention. This is the mandate of environmental protection authority of Ethiopia. But the rules and regulations regarding environmental quality is not practically followed and the authority is not taking any action when the rules are not adhered to by the industries. Therefore, following specific suggestions are made for addressing the water scarcity issues in Awash basin:

The study shows that availability of water in the basin cannot meet the current demand of water for different uses. This calls for improving water management and raising the level of awareness among the stakeholder about the gap between supply and demand of water in the basin. Decision makers should act vigorously to bring about equitable and rational use of water by different sectors so as to avoid overuse and wastage of water.

Stakeholder participation in all phases of water resources development should be given a weightage and should be encouraged. Water should be fairly shared among upstream and downstream users and between regions. The sectorial water use must be quantified, and all discharge measuring points should be renovated to know the volume of water abstracted for different purposes at different points.

Minimization of losses of water in irrigation and unaccounted losses in water supply systems is required. Irrigation efficiency should be improved by introducing current technologies to minimize/avoid water losses.

Water pollution standards should be established and enforced by law. Industries should treat their discharges to an acceptable level before letting it into water systems. The minimum allowable polluting substances to be let into water system should be fixed by a competent authority.

The price of water should discourage overuse of the resource and the costs of water supply should be recovered. Environmental and social impacts of water scarcity should be averted by improving the weak cross-sectorial integration which is involved in water management in one way or the other.

Loss of biodiversity and ecosystem service is brought about by degradation of water resources. So in order to avoid overuse of water and maximize the water use efficiency, water should be managed in an integrated way. Integrated water resources management should be designed in the basin to address the economic development combined with the needs of the environment to sustain development. This requires coordination among sectors, and replacement of fragmented resource management with coordinated and participatory process. Integrated water resources management framework should encompass ecosystem services that would enable the realization of a broad benefit from well-managed water and other related natural resources. This benefit may include both flood and drought mitigation, wildlife habitat conservation and the like. In integrated water resources management, the traditional top-down management approach should be supplemented by bottom-up approach. This is important in integrating and harmonizing various stakeholders’ views and interest.

Environmental flow is the most important variable that impacts river morphology, aquatic habitat and water quality. The Awash basin river ecosystem is deteriorating significantly due to overuse of water for different purposes. Environmental flows which closely follow the natural flow regime are needed for ecosystem health (Jain 2012 ). The adverse impacts that result from water storage and/or diversion of river flows can be mitigated by releasing water to satisfy environmental water requirements. To achieve the desired balance of economic benefits and environmental costs, the fraction of mean annual flow (MAF) that can be abstracted/released should be decided depending on different factors like size of the river (Jain 2012 ). Awash river basin has a religious and cultural values attached to it. The Oromo people living in the basin exercise religious rituals called Irrecha. In view of this, 35 % of the MAF of the river is allocated to the environmental flow to ensure that there is enough depth and discharge of good quality water in the river. This recommendation also helps rehabilitate/restore the current deteriorating floodplains and riparian vegetation of the basin. Once the current condition of the basin has been improved, the environmental flow requirement can be reduced to 8–10 % of the mean annual flow to avail minimum water for people and basic survival of aquatic lives.

Conclusions

This study developed a surface water balance for Awash basin using SWAT model. Water balance studies can be used to assess the effect of anthropogenic activities and climate change on the volume of water that the basin can supply. It also helps establish the relationship between rainfall and runoff for forecasting purposes, the rational use of water and its redistribution in space and time. The annual water balance for Awash river basin was evaluated taking into account all the parameters that could be evaluated. The water balance calculation for the basin revealed that the basin is water deficit. The total surface water yield of the basin is estimated to be 4.64 BCM, while the total demand is about 4.67 BCM. This shows that there is a deficit of 0.03 BCM/year of surface water in the basin.

The seasonal water deficit is even very serious. The monthly deficit and surplus of water is calculated for the last 2 years of the study period. During December to April month of the year 2011, the basin shows a deficit of 1.27 BCM, while there is an excess water of 1.67 BCM during the months of May to September. In 2012, during the similar months, there is a deficit of 2.82 BCM, whereas there is a surplus of 3.16 BCM of water during June–October.

Addressing the challenges of water scarcity will require both selective development and exploitation of new water supplies and comprehensive policy reform that encourages more efficient use of existing water supplies. Exploitation of new water supply like harvesting rainwater and storing the excess flood during rainy period can alleviate water scarcity in the basin to a great extent. So the immediate future task of the decision makers should be to protect the ecology of the basin from further deterioration of the resources and exploit different sources of water to mitigate the current water scarcity.

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Acknowledgments

The authors are very grateful to editor of sustainable water management journal and two anonymous reviewers for their constructive comments on an earlier version of the manuscript that have enriched the contents of the paper. However, the views expressed here are those of the authors alone.

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Adeba, D., Kansal, M.L. & Sen, S. Assessment of water scarcity and its impacts on sustainable development in Awash basin, Ethiopia. Sustain. Water Resour. Manag. 1 , 71–87 (2015). https://doi.org/10.1007/s40899-015-0006-7

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Received : 24 February 2015

Accepted : 21 April 2015

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Issue Date : May 2015

DOI : https://doi.org/10.1007/s40899-015-0006-7

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A paper published in the January 2024 issue of the Journal of the Association of Environmental and Resource Economists examines this paradox and finds that the benefits to consumers from input-efficiency adoption are, on average, negative. In "Input Efficiency as a Solution to Externalities and Resource Scarcity: A Randomized Controlled Trial," authors Francisco Alpizar, Maria Bernedo Del Carpio, and Paul J. Ferraro conclude that, with respect to the input-efficient technologies that they study, no efficiency paradox exists.

Much of the data regarding the efficiency paradox has been taken from the energy-efficient context. In "Input Efficiency," the authors report instead on a randomized controlled trial (RCT) of water-efficient technology adoption. The trial took place in Costa Rica, where the overexploitation of public aquifers is a pressing concern. Nearly 900 households, from a group of over 1300 households, were selected at random to receive water-efficient showerheads and faucet aerators. Engineering methods predicted an average reduction in water use of about 30%, whereas the actual reduction in the trial was only about 9%. According to the authors, that gap between prediction and reality stemmed from a set of faulty engineering and behavioral assumptions. For example, engineers assume households do not change their behaviors after the technology is adopted, whereas survey data suggested that households often left the water running longer to compensate for the lower flow rate of the efficient devices. When the authors assess how the participating households value the water savings, which are both uncertain and realized over many years, and compared this value to the upfront cost of purchasing the technologies, they conclude that, for the average user, the net benefits of these input-efficient technologies are negative.

The absence of a water efficiency paradox -- in other words, the absence of a win-win outcome for the environment and the people -- means that simply doing a better job of informing consumers about the advantages of input-efficient devices will not be an effective strategy for mitigating resource scarcity or adapting to climate change. As noted by the authors of "Input Efficiency," their results suggest that "consumer misinformation may not be the main driver of low adoption rates" of efficient technologies. Rather, the main driver is simply the modest savings from the technologies combined with the uncertainty and delayed nature of those savings. "In summary," they note, "claims of a 'win-win' outcome associated with the adoption of input-efficient technologies in our study context are not supported by the data." To address water scarcity and mitigate the effects of a changing climate in their study area, other solutions will be necessary.

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  • Francisco Alpizar, María Bernedo Del Carpio, Paul J. Ferraro. Input Efficiency as a Solution to Externalities and Resource Scarcity: A Randomized Controlled Trial . Journal of the Association of Environmental and Resource Economists , 2024; 11 (1): 171 DOI: 10.1086/725700

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Scientists find about a quarter million invisible nanoplastic particles in a liter of bottled water

The average liter of bottled water has nearly a quarter million invisible pieces of ever so tiny nanoplastics, detected and categorized for the first time by a microscope using dual lasers. (Jan. 8) (AP Video: Mary Conlon)

FILE - Tourists fill plastic bottles with water from a public fountain at the Sforzesco Castle, in Milan, Italy, June 25, 2022. A new study found the average liter of bottled water has nearly a quarter million invisible pieces of nanoplastics, microscopic plastic pieces, detected and categorized for the first time by a microscope. (AP Photo/Luca Bruno, File)

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Naixin Qian, a Columbia physical chemist, demonstrates the glass filtration apparatus used to test water samples for nanoplastics, microscopic plastic pieces, in New York on Monday, Jan. 8, 2024. The average liter of bottled water has nearly a quarter million invisible pieces of nanoplastics, detected and categorized for the first time by a microscope. (AP Photo/Mary Conlon)

The inside of an optical box reveals the components that organize the light from laser beams to identify nanoplastics, microscopic plastic pieces, in New York on Monday, Jan. 8, 2024. A new study found the average liter of bottled water has nearly a quarter million invisible pieces of nanoplastics, detected and categorized for the first time by a microscope. (AP Photo/Mary Conlon)

Naixin Qian, a Columbia physical chemist, demonstrates the placement of a sample for nanoplastics, microscopic plastic pieces, in New York on Monday, Jan. 8, 2024. A new study found the average liter of bottled water has nearly a quarter million invisible pieces of nanoplastics, detected and categorized for the first time by a microscope. (AP Photo/Mary Conlon)

Naixin Qian, a Columbia physical chemist, zooms in on an image generated from a microscope scan, with nanoplastics, microscopic plastic pieces, appearing as bright red dots in New York on Monday, Jan. 8, 2024. A new study found the average liter of bottled water has nearly a quarter million invisible pieces of nanoplastics, detected and categorized for the first time by a microscope. (AP Photo/Mary Conlon)

research paper on scarcity of water

The average liter of bottled water has nearly a quarter million invisible pieces of ever so tiny nanoplastics, detected and categorized for the first time by a microscope using dual lasers.

Scientists long figured there were lots of these microscopic plastic pieces, but until researchers at Columbia and Rutgers universities did their calculations they never knew how many or what kind. Looking at five samples each of three common bottled water brands, researchers found particle levels ranged from 110,000 to 400,000 per liter, averaging at around 240,000 according to a study in Monday’s Proceedings of the National Academy of Sciences.

These are particles that are less than a micron in size. There are 25,400 microns — also called micrometers because it is a millionth of a meter — in an inch. A human hair is about 83 microns wide.

Previous studies have looked at slightly bigger microplastics that range from the visible 5 millimeters, less than a quarter of an inch, to one micron. About 10 to 100 times more nanoplastics than microplastics were discovered in bottled water, the study found.

FILE - Tourists fill plastic bottles with water from a public fountain at the Sforzesco Castle, in Milan, Italy, June 25, 2022. A new study found the average liter of bottled water has nearly a quarter million invisible pieces of nanoplastics, microscopic plastic pieces, detected and categorized for the first time by a microscope. (AP Photo/Luca Bruno, File)

Tourists fill plastic bottles with water from a public fountain at the Sforzesco Castle, in Milan, Italy, June 25, 2022. (AP Photo/Luca Bruno)

Much of the plastic seems to be coming from the bottle itself and the reverse osmosis membrane filter used to keep out other contaminants, said study lead author Naixin Qian, a Columbia physical chemist. She wouldn’t reveal the three brands because researchers want more samples before they single out a brand and want to study more brands. Still, she said they were common and bought at a WalMart.

Researchers still can’t answer the big question: Are those nanoplastic pieces harmful to health?

“That’s currently under review. We don’t know if it’s dangerous or how dangerous,” said study co-author Phoebe Stapleton, a toxicologist at Rutgers. “We do know that they are getting into the tissues (of mammals, including people) … and the current research is looking at what they’re doing in the cells.”

FILE - The cracked earth of the Sau reservoir is visible north of Barcelona, Spain, March 20, 2023. Earth last year shattered global annual heat records, the European climate agency said Tuesday, Jan. 9, 2024. (AP Photo/Emilio Morenatti, File)

The International Bottled Water Association said in a statement: “There currently is both a lack of standardized (measuring) methods and no scientific consensus on the potential health impacts of nano- and microplastic particles. Therefore, media reports about these particles in drinking water do nothing more than unnecessarily scare consumers.”

The American Chemistry Council, which represents plastics manufacturers, declined to immediately comment.

The world “is drowning under the weight of plastic pollution, with more than 430 million tonnes of plastic produced annually” and microplastics found in the world’s oceans , food and drinking water with some of them coming from clothing and cigarette filters, according to the United Nations Environment Programme. Efforts for a global plastics treaty continue after talks bogged down in November.

Naixin Qian, a Columbia physical chemist, zooms in on an image generated from a microscope scan, with nanoplastics, microscopic plastic pieces, appearing as bright red dots in New York on Monday, Jan. 8, 2024. A new study found the average liter of bottled water has nearly a quarter million invisible pieces of nanoplastics, detected and categorized for the first time by a microscope. (AP Photo/Mary Conlon)

Naixin Qian, a Columbia physical chemist, zooms in on an image generated from a microscope scan, with nanoplastics, microscopic plastic pieces, appearing as bright red dots in New York on Monday, Jan. 8, 2024. (AP Photo/Mary Conlon)

All four co-authors interviewed said they were cutting back on their bottled water use after they conduced the study.

Wei Min, the Columbia physical chemist who pioneered the dual laser microscope technology, said he has reduced his bottled water use by half. Stapleton said she now relies more on filtered water at home in New Jersey.

But study co-author Beizhan Yan, a Columbia environmental chemist who increased his tap water usage, pointed out that filters themselves can be a problem by introducing plastics.

“There’s just no win,” Stapleton said.

Outside experts, who praised the study, agreed that there’s a general unease about perils of fine plastics particles, but it’s too early to say for sure.

“The danger of the plastics themselves is still an unanswered question. For me, the additives are the most concerning,” said Duke University professor of medicine and comparative oncology group director Jason Somarelli, who wasn’t part of the research. “We and others have shown that these nanoplastics can be internalized into cells and we know that nanoplastics carry all kinds of chemical additives that could cause cell stress, DNA damage and change metabolism or cell function.”

Somarelli said his own not yet published work has found more than 100 “known cancer-causing chemicals in these plastics.”

What’s disturbing, said University of Toronto evolutionary biologist Zoie Diana, is that “small particles can appear in different organs and may cross membranes that they aren’t meant to cross, such as the blood-brain barrier.”

Diana, who was not part of the study, said the new tool researchers used makes this an exciting development in the study of plastics in the environment and body.

About 15 years ago, Min invented dual laser microscope technology that identifies specific compounds by their chemical properties and how they resonate when exposed to the lasers. Yan and Qian talked to him about using that technique to find and identify plastics that had been too small for researchers using established methods.

Kara Lavender Law, an oceanographer at the Sea Education Association, said “the work can be an important advance in the detection of nanoplastics” but she said she’d like to see other analytical chemists replicate the technique and results.

Denise Hardesty, an Australian government oceanographer who studies plastic waste, said context is needed. The total weight of the nanoplastic found is “roughly equivalent to the weight of a single penny in the volume of two Olympic-sized swimming pools.”

Hardesty is less concerned than others about nanoplastics in bottled water, noting that “I’m privileged to live in a place where I have access to ‘clean’ tap water and I don’t have to buy drinking water in single use containers.”

Yan said he is starting to study other municipal water supplies in Boston, St. Louis, Los Angeles and elsewhere to see how much plastics are in their tap water. Previous studies looking for microplastics and some early tests indicate there may be less nanoplastic in tap water than bottled.

Even with unknowns about human health, Yan said he does have one recommendation for people who are worried: Use reusable bottles instead of single-use plastics.

Read more of AP’s climate coverage at http://www.apnews.com/climate-and-environment

Follow Seth Borenstein on X, formerly known as Twitter, at @borenbears

Associated Press climate and environmental coverage receives support from several private foundations. See more about AP’s climate initiative here. The AP is solely responsible for all content.

SETH BORENSTEIN

Water Scarcity and Its Effects on the Environment Research Paper

Introduction, types of water scarcity, works cited.

The core objective of this research paper is to examine water scarcity and its effects to the environment. This research paper will lean towards a descriptive approach. Several causes of water scarcity will be reviewed in this research and subsequently suggest solutions to the problems will be discussed.

In conclusion, this research paper will make a number of recommendations to ensure significant strides are achieved in curbing water scarcity. Besides, after reviewing the recommendations applied, this paper will determine ways in which the research results can be dispersed. Introduction

This report will assess the increased demand for water resources as a result of its unavailability. Besides, the paper will also consider the solutions and recommendations for supplying water to all. Water is a valuable resource to humans and the world as a whole.

If water resources continue to diminish, the environment will continue to experience the struggle of surviving since the environment, and forests particularly depend on water resources. Huge industrial demand for water, increased populations and agricultural demands for water increase the scarcity of water. Australia, for instance, is estimated to maintain its domestic water needs rise to 70 percent in the near future. Water Scarcity

Water scarcity is a problem that is experienced all over the world. It is estimated that over a billion people are annually hit by water scarcity. The U.S. department of state puts a figure of 1.1 billion people who lack safe drinking water while 2.4 billion cannot access basic sanitation. Interestingly, “water scarcity also occurs in regions that contain freshwater and sufficient amounts rainfall” (Postel 85).

This is because sufficiency of water supply depends on water conservation methods, distribution channels available in the community and the quality of water as stated by Postel (192). Besides, meeting the demand for household water use, farms, industry and the environment requires substantial conservation methods and timely distribution methods. It is estimated that one out of every three people on each continent of the globe is affected by water scarcity.

As the world population grows the need for more water also increases. Besides, more urban cities are coming up, and urbanization increases the household and industrial consumption. 1.2 billion people across the globe live in areas where water is not present or is physically not available. This is a fifth of the world’s population.

Water Scarcity in Africa.

Fig. 1.1 (Tag Archive for ‘Water Scarcity’)

Fig. 1.2 (BBC NEWS)

As shown by the above figure, water scarcity is fast becoming a major challenge in developing countries where a quarter of the world population lives. This is due to “lack of proper technique of supplying water from sources such as rivers and aquifers to where it is needed most” (Berk 190). In places where water shortage is experienced, communities are forced to use unsafe drinking water for drinking and washing their clothes.

Unsafe drinking water increases the chances of water borne diseases such as dysentery, cholera and typhoid fever being transmitted to humans. Furthermore, “water scarcity can lead to other diseases including trachoma, which is an eye infection that leads to blindness, plague and typhus” (Pereira and Lacovides 299). When people are faced with water scarcity, they institute measures to store water in their home. These measures can include using water tanks or sinking wells.

This method leads to a breeding ground for mosquitoes – which are known carriers of malaria and dengue fever among others. In the face of all this problems associated with water scarcity, there arises a need to address the issue of water scarcity before it gets out of hand. Better water management policies ensure safety of the communities relying on the water as breeding grounds for insects are eliminated, hence a reduction in water borne diseases like the schistosomiasis which is a devastating illness.

According to Sherbinin (26) the shortage of water and agricultural production in poor urban settings utilizes waste water. More than 10% of the world’s population consumes foods that have been grown using waste water.

These irrigated foods can contain harmful chemicals or disease-causing organisms. It may almost seem ironical to note that the world has enough water for everyone. However, the problem that leads to water shortage is poor distribution. “Water scarcity is a natural occurrence in some areas. However, in others areas it is a man-made phenomenon” (Sherbinin 26).

Similarly, the world is endowed with sufficient water resource to cater for approximately 6 billion people. According to Pereira and Lacovidae 302) scarcity has contributed to uneven distribution channels, wastage. This is because of poor harvest and utilization strategies. Poor methods of handling the water resource have led to water Pollution. Hence, this has created a big challenge that threatening the ecosystem and human population.

Physical Scarcity

Physical scarcity of water is prevalent across the world. As the name suggests, access to water sources is physically limited. This happens when the demand for water surpasses the land’s capacity to provide the much-needed water. This form of deficiency is primarily associated with the dry parts of the world, including arid regions of the globe as clearly illustrated by the figure below.

The northern part of Africa and some parts in Asia and Australia are the worst hit by this physical scarcity. However, we have some regions in the world which do not fall in the dry land category but have man-made physical scarcity. For instance, the Colorado River basin has been “over used causing physical water scarcity downstream” (Pereira and Lacovides 299). Thus, scarcity can also be attributed to over management of the river resources.

Below is Figure 1.3 showing water scarcity distribution around the globe (BBC NEWS)

Economic Scarcity

The most problematic type of water scarcity is economic water scarcity. This happens when no concrete measures are taken to ensure water availability. This situation persists largely due to lack of good governance, and lack of good will to change the situation. Therefore, economic scarcity is demonstrating the lack of resources in terms of funds or monetary benefit to utilize available sources of water.

The sub-Saharan Africa falls under this model of economic water scarcity. Unequal water resource distribution is generally experienced in the Sub-Saharan due to several reasons. These reasons are tied to political and ethnic conflicts, which are a common occurrence in this part of the world.

As shown in Fig 1.2 much of sub-Saharan Africa falls under economic water scarcity. However, Odgaard explains that in the presence of good governance mechanisms, this situation is manageable (140). In most cases, access to clean and safe water can be as simple as constructing small dams for communities to harvest rain water. Besides, the principal objective should be to provide relief for the already suffering communities.

To ensure clean water is available to world population, water harvesting techniques should be developed. These need not be complicated as it may mean rain water collection from roof tops and construction of water storage tanks. Without question, this situation can be tackled with the construction effort from the local community, availability of funds and engineering.

Water Scarcity in the U.S

As highlighted earlier in this research paper, water shortage is a global concern that is affecting communities and the environment and threatens to affect many others if substantial measures are not taken to tackle the scarcity.

However, it is difficult to compare the struggle of an African woman walking long distances in search of fresh water with water scarcity as experienced in the United States. The Colorado River is beginning to run dry in some places; this sounds almost impossible considering the size of the river. Huge water bodies like Lake Mead found in Arizona may become obsolete.

These are some of the dramatic changes that are facing the United States with regard to water scarcity. With this realization, more and more people are starting to connect with situations in dry regions of the globe. More so, the effects of water mismanagement are starting to be felt. Research indicates that Lake Mead may run dry by the year 2012. This is a serious issue considering the lake currently supplies up to 22 million people with water.

Drought on the lake.

Figure 1.4 shows Lake Mead’s receding water levels (KTAR).

This is proof enough that water scarcity is not just a problem of people who never had water but rather a problem for all. Demand for more water and problems associated with pollution is contributing factor to water shortages. The daily demand for water means that the availability of the same will be affected in the future. Many people may thirst in the future if the current trend of wasteful toilet flushes and showerheads are not minimized.

Key Causes of Water Scarcity

Water scarcity has been caused by increased demand. These demands can be categorized into five major contributors to water shortage. Firstly, industrial water consumption enhances their production has created a strain on water resources. Most industries require having sufficient water supplies in order to perform optimally and produce goods or services.

Besides, most mining and oil industries use water in their operations. Thus, water scarcity makes these industries to be more susceptible to water shortages. Secondly, agricultural water needs for farms where there is unreliable rainfall create a huge demand for water, thus exerting more pressure on the already strained water resources.

Links Between Population and Fresh Water.

Fig. 1.5 (Links between population and fresh water)

As the world population grows, more demand for water is experienced as illustrated by fig 1.4. The world population recently hit 7 billion, and the figure could only mean that pressure to supply water for all is expected to rise. Consumer demand is closely linked to population growth as more and more households require water to maintain their households.

Economic growth is a positive step towards improving the lives of people in a given community, but calls for the need to supply resources to fuel it. One of it is water; hence as more economic growth is experienced more demand for water is created.

Suggested Solutions to Water Scarcity

Environmentalists maintain that immediate solutions have to be devised. Low cost solutions come in handy. In China for instance, farmers are already making use of these inexpensive water conservation methods with great results (FFTC). However, “low cost solutions, for example, creating still water conservation may harm the population downstream” (Berk 190). Therefore, it is important for the conservation efforts to involve everyone to provide an amicable solution for all.

Global Water Consumption.

Fig. 1.6 showing the global water usage (Umwelt Bundes Amt)

In order to ensure water scarcity is effectively tackled, total commitment to set targets and solutions is required. Figure 1.5 clearly indicates that the demand for water is rising, and as a matter of urgency, conservation efforts will bear fruit if every one of us realizes that they have a role to play.

Constant assessment of the strategies governing water bodies and their utilization will ensure that positive progress is achieved. Though much effort has been focused on water conservation, its use and proper management should be emphasized as it will ensure clean water service delivery for us and generations to come. Moreover, focus on climate changes and environmental degradation should also be improved, and a positive environmental culture encouraged.

BBC NEWS. Map Details, Global Water Stress . 2006. Web.

Berk, Richard. Water Shortage: Lessons in Conservation from the Great California Drought . Halifax: Abt Books, 1981. Print.

FFTC. Irrigation Management in Rice-Based Cropping Systems: Issues and Challenges in Southeast Asia. ” 1998. Web.

KTAR. As Lake Meads Drops, Water Concerns Rise . 2010. Web.

Links between Population and Fresh Water. Population Growth and Water. 1996. Web.

Odgaard, Rie . Conflicts over land & water in Africa. Michigan: MSU Press, 2007. Print.

Pereira, Cordery and Lacovides. Coping With Water Scarcity, Addressing the Challenges. New York: Springer, 2009. Print.

Postel, Sandra. The Last Oasis: Facing Water Scarcity. Oxford: Earthscan, 1992. Print.

Sherbinin, Alex. Water and Population Dynamics: Local Approaches to a Global Challenge. Montreal: IUCN, 2009. Print.

Tag Archive for ‘Water Scarcity’ . “ Hydro-diplomacy” Needed to Avert Arab Water Wars . 2011. Web.

Umwelt Bundes Amt . Exhibitions from the Umwelt bundes amt (Federal Environment Agency) . 2010. Web.

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Here’s what you’re really swallowing when you drink bottled water

A new study finds that ‘nanoplastics’ are even more common than microplastics in bottled water.

research paper on scarcity of water

People are swallowing hundreds of thousands of microscopic pieces of plastic each time they drink a liter of bottled water, scientists have shown — a revelation that could have profound implications for human health.

A new paper released Monday in the Proceedings of the National Academy of Sciences found about 240,000 particles in the average liter of bottled water, most of which were “nanoplastics” — particles measuring less than one micrometer (less than one-seventieth the width of a human hair).

For the past several years, scientists have been looking for “microplastics,” or pieces of plastic that range from one micrometer to half a centimeter in length, and found them almost everywhere. The tiny shards of plastic have been uncovered in the deepest depths of the ocean , in the frigid recesses of Antarctic sea ice and in the human placenta . They spill out of laundry machines and hide in soils and wildlife. Microplastics are also in the food we eat and the water we drink: In 2018, scientists discovered that a single bottle of water contained, on average, 325 pieces of microplastics .

But researchers at Columbia University have now identified the extent to which nanoplastics also pose a threat.

“Whatever microplastic is doing to human health, I will say nanoplastics are going to be more dangerous,” said Wei Min, a chemistry professor at Columbia and one of the authors of the new paper.

Scientists have also found microplastics in tap water, but in smaller amounts.

Sherri Mason, a professor and director of sustainability at Penn State Behrend in Erie, Pa., says plastic materials are a bit like skin — they slough off pieces into water or food or whatever substance they are touching.

“We know at this point that our skin is constantly shedding,” she said. “And this is what these plastic items are doing — they’re just constantly shedding.”

The typical methods for finding microplastics can’t be easily applied to finding even smaller particles, but Min co-invented a method that involves aiming two lasers at a sample and observing the resonance of different molecules. Using machine learning, the group was able to identify seven types of plastic molecules in a sample of three types of bottled water.

“There are some other techniques that have identified nanoplastics before,” said Naixin Qian, a PhD student in chemistry at Columbia and the first author of the new paper. “But before our study, people didn’t have a precise number of how many.”

“It’s really groundbreaking,” said Mason, who was not involved in the research but was one of the first researchers to identify plastics in bottled water. The new study, she says, shows how extensive nanoplastics are and provides a starting point to assess their health effects.

“Normal humans looking at a sample of water — if there’s visible plastic in it, they’ll be turned off,” she said. “But they don’t realize that it’s actually the invisible plastics present that are the biggest concern.”

The new study found pieces of PET (polyethylene terephthalate), which is what most plastic water bottles are made of, and polyamide, a type of plastic that is present in water filters. The researchers hypothesized that this means plastic is getting into the water both from the bottle and from the filtration process.

Researchers don’t yet know how dangerous tiny plastics are for human health. In a large review published in 2019, the World Health Organization said there wasn’t enough firm evidence linking microplastics in water to human health, but described an urgent need for further research.

In theory, nanoplastics are small enough to make it into a person’s blood, liver and brain. And nanoplastics are likely to appear in much larger quantities than microplastics — in the new research, 90 percent of the plastic particles found in the sample were nanoplastics, and only 10 percent were larger microplastics.

Jill Culora, a spokeswoman for the International Bottled Water Association, said in an email that there “is both a lack of standardized methods and no scientific consensus on the potential health impacts of nano- and microplastic particles. Therefore, media reports about these particles in drinking water do nothing more than unnecessarily scare consumers.”

Finding a connection between microplastics and health problems in humans is complicated — there are thousands of types of plastics, and over 10,000 chemicals used to manufacture them. But at a certain point, Mason said, policymakers and the public need to prepare for the possibility that the tiny plastics in the air we breathe, the water we drink and the clothes we wear have serious and dangerous effects.

“You still have a lot of people that, because of marketing, are convinced that bottled water is better,” Mason said. “But this is what you’re drinking in addition to that H2O.”

More on climate change

Understanding our climate: Global warming is a real phenomenon , and weather disasters are undeniably linked to it . As temperatures rise, heat waves are more often sweeping the globe — and parts of the world are becoming too hot to survive .

What can be done? The Post is tracking a variety of climate solutions , as well as the Biden administration’s actions on environmental issues . It can feel overwhelming facing the impacts of climate change, but there are ways to cope with climate anxiety .

Inventive solutions: Some people have built off-the-grid homes from trash to stand up to a changing climate. As seas rise, others are exploring how to harness marine energy .

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Massive amounts of tiny plastics found in bottled drinking water, study finds

Researchers found thousands of plastic fragments in a liter of bottled water.

Drinking more water every day is a healthy habit, but a new study has raised concerns about the container you should sip from.

Researchers from Columbia University and Rutgers University published the study Monday in the Proceedings of the National Academy of Sciences , which reveals an average of 240,000 detachable plastic fragments were found in a standard liter of bottled water.

PHOTO: In this undated stock photo, a person is seen drinking out of a plastic water bottle.

Although the tiny "nanoplastics," which are smaller than one micrometer in size – less than one-seventieth the width of a human hair – may seem too small to be an issue, the data showed a large jump in concentrations found in bottled water.

Concentrations of micro-nano plastics found in testing were estimated to be 240,000 particles on average per liter of bottled water, "about 90% of which are nanoplastics," researchers wrote in the paper, after testing three unidentified brands of bottled water.

"This is orders of magnitude more than the microplastic abundance reported previously in bottled water," the paper notes.

PHOTO: In this undated stock photo, plastic water bottles are seen on a conveyor belt.

"Individual particles for all seven plastic polymers from the library were identified, enabling statistical analysis of plastic particles with sizes down to 100 to 200 [nanometers]," the researchers said.

The International Bottled Water Association (IBWA) responded to the study, saying in part that there is "both a lack of standardized methods and no scientific consensus on the potential health impacts of nano- and microplastic particles," and adding that "media reports about these particles in drinking water do nothing more than unnecessarily scare consumers."

The IBWA also noted that the organization had "very limited notice and time to review this new study closely" and so "cannot provide a detailed response at this time."

For years, scientists have looked for microplastics, which can measure anywhere from one micrometer to half a centimeter in size. But identifying and analyzing nanoplastics, which are far smaller, presented a greater challenge. In response, researchers in the new study developed a "hyperspectral stimulated Raman scattering (SRS) imaging platform with an automated plastic identification algorithm" – essentially, using laser technology combined with computer analysis and machine learning – to enable identification and analysis of particles of plastics "at the single-particle level," according to the report.

MORE: Video Microplastics found in human bloodstreams

Pieces of tiny plastics have previously been found in oceans, beaches and even tap water.

PHOTO: In this undated stock photo, a woman is seen unscrewing a plastic water bottle.

Phoebe Stapleton, a professor of pharmacology and toxicology at Rutgers University and co-author of the new study, said that scientists have known nanoplastics were in water, but explained, "if you can't quantify them or can't make a visual of them, it's hard to believe that they're actually there."

The new findings can help further study and identify the extent that nanoplastic consumption by humans may pose a health threat.

In 2022, the World Health Organization said there wasn't enough evidence "for reliable characterization and qualification of the risks to human health" adding the need for further research.

Although microplastics have been discovered in people's lungs, blood and excrement, scientists have said evidence that the particles may be harmful to human health has so far been inconclusive.

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  3. (PDF) ARTICLE: Water Scarcity: An Alternative View and Its Implications

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COMMENTS

  1. (PDF) Water Supply and Water Scarcity

    This paper provides an overview of the Special Issue on water supply and water scarcity. The papers selected for publication include review papers on water history, on water management...

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  5. Water scarcity assessments in the past, present and future

    Water scarcity has become a major constraint to socio-economic development and a threat to livelihood in increasing parts of the world. Since the late 1980s, water scarcity research has attracted much political and public attention.

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    This article investigates the relation between water scarcity and water management. There are many different perceptions of water scarcity, which can include the conditions of arid environments, a general lack of access to water, insufficient water at a basin scale, or difficulty in meeting competing needs. All these issues will intensify with ...

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  12. Water

    Water Supply and Water Scarcity Print Special Issue Flyer Special Issue Editors Special Issue Information Keywords Published Papers A special issue of Water (ISSN 2073-4441). This special issue belongs to the section "Water Use and Scarcity". Deadline for manuscript submissions: closed (31 May 2020) | Viewed by 117285 Printed Edition Available!

  13. PDF Water Scarcity and Poverty

    In this paper, we discuss the implications for poverty alleviation of growing water scarcity with particular reference to South Asia and sub-Saharan Africa. First, we briefly summarize the impact of irrigation development on poverty alleviation in South Asia in the recent past.

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    Water scarcity adaptation drivers have multiple facets, approaches and explanations. The conceptualization of water scarcity has shifted from emphasis on scientific information and specific technologies to research on cultural environments and institutions ( Wolfe, S. & Brooks, 2003 ).

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    Equitable access and rational use of water resources is important to cope with water scarcity. The optimal allocation of limited water resources for various purposes is required for sustainable development. Awash river basin is one of the most utilized river basins in Ethiopia. There is increasing demand for water due to recent population growth in the basin because of Urbanization. Excessive ...

  18. PDF Research Report

    Water Scarcity and the Role of Storage in Development Andrew Keller R. Sakthivadivel and David Seckler International Water Management Institute Research Reports

  19. No win-win? Input-efficient technologies might not be so efficient

    To address natural resource scarcity, pollution, and other harmful effects of climate change, some scientists and policymakers emphasize the adoption of input-efficient technologies like water ...

  20. Water scarcity assessments in the past, present, and future

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  21. Scientists find quarter million nanoplastic particles in a liter of

    Updated 1:11 PM PST, January 8, 2024. The average liter of bottled water has nearly a quarter million invisible pieces of ever so tiny nanoplastics, detected and categorized for the first time by a microscope using dual lasers. Scientists long figured there were lots of these microscopic plastic pieces, but until researchers at Columbia and ...

  22. Water Scarcity and Its Effects on the Environment Research Paper

    The core objective of this research paper is to examine water scarcity and its effects to the environment. This research paper will lean towards a descriptive approach. Several causes of water scarcity will be reviewed in this research and subsequently suggest solutions to the problems will be discussed. We will write a custom essay on your topic

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    One big focus of research: bottled water, which has been shown to contain tens of thousands of identifiable fragments in each container. Now, using newly refined technology, researchers have entered a whole new plastic world: the poorly known realm of nanoplastics, the spawn of microplastics that have broken down even further. ...

  25. Scientists discover 100 to 1000 times more plastics in bottled water

    A new paper released Monday in the Proceedings of the National Academy of Sciences found about 240,000 particles in the average liter of bottled water, most of which were "nanoplastics ...

  26. (PDF) Water Scarcity in the Twenty-First Century

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  28. (PDF) Water Scarcity: Problems and Possible solutions

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