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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
- Developing world
- Water resources
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.
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.
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.
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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A.B. designed the manuscript, selecting the references, assembling the materials, processing the data, and organizing the first draft. L.R. then contributed to the writing of the manuscript. A.B. then further changed the manuscript addressing the reviewers’ comments.
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Solutions to Water Crises (Related to Actual Interventions)
Editorial: Solutions to Water Crises (Related to Actual Interventions)
- 1 Indian Institute of Technology Kharagpur, India
- 2 Swiss Federal Institute of Aquatic Science and Technology, Switzerland
- 3 Portland State University, United States
- 4 Delft University of Technology, Netherlands
- 5 Wageningen University and Research, Netherlands
- 6 Kansas State University, United States
- 7 University College London, United Kingdom
The final, formatted version of the article will be published soon.
Editorial: Solutions to Water Crises (Related to Actual Interventions) Jenia Mukherjee, Sara Marks, Melissa Haeffner, Saket Pande, Pieter Van Oel, Matthew Sanderson and Adriana Allen Water science has become "pluralistic" (Evers et al. 2017) to collectively (yet differently) understand complex water systems with promising combinations of compatible and complementary disciplines.The contemporary context of water science discusses the more severe water-society challenges of the Anthropocene. Yet, the conversation is not definitive; indeed, there are unending debates between quantitative and qualitative research approaches including methodological choices and accuracies along questions of scales, themes, and politics of funding. Transdisciplinary applications and cross-sectoral engagements offer solution-oriented water just trajectoriesscientists, practitioners, and user groups designing and deploying 'solutions' related to actual interventions in addressing water crisis.However, 'solutions' has its own baggage. Mainstream solution designs and implementation strategies are not free from the dangers and dogmas of 'path-dependence' (Mahoney and Schensul 2006). That is, they are often heavily loaded with lineages from the past, and with limited capacities to solve problems that are 'wicked'multi-dimensional, dynamic, and recurring. The post-development era on 'sustainability' (Castro 2004) takes us through the critical 'solution' route at global scales, when development agencies desperately transported and transplanted 'first world' solutions on the 'third world' 'poor', 'uncertain', and 'ignorant' communities, resulting into development of underdevelopment (Frank 1969), distinctly demonstrating the problematic aspects of universally designed prescriptive solution packages, manufactured in alienated contexts (Therkildsen 1998) But are 'local', 'small-scale', 'community-based' adaptive practices effective and efficient enough to solve environmental/water crises, with far flung outcomes and impacts within and beyond situated geographies? The answer is not simple; it is unwise to fall prey to binary reductionisms, pitting 'small' against 'big', 'cost-effective' against 'costly', 'ecofriendly' against 'environmentally malign', and 'indigenous' against 'modern'. The authors have problematized 'solutions' with rich, diverse, dense, and in-depth empirical investigations using transdisciplinary water-society perspectives.Basel et al. unveils the paradoxes within the otherwise hydrologically and socially promising smallscale managed aquifer recharge (MAR), exemplifying "how such interventions play out within the complexity of the socio-hydrological system in which they are implemented" (p. 1). Here, the application of political ecology enables the authors to study the interplay between biophysical, climate, and social systems and account for both positive (drought reduction chances) and negative feedback loops (time lag between implementation and benefits reducing community willingness to act). Thus, they scientifically refrain from overestimating or oversimplifying small-scale MAR as a solution, while advocating for its practical implementation. The article underscores place-based dynamics in determining complex human-water interactions within and beyond local landscapes, emphasizing the need to critically understand climate trends using a power-sensitive approach, sensitizing us with nonlinearities and complexities socially embedded in small-scale MAR.Solutions at micro-settings with household as the unit of analysis Mukherjee et al. off-loads social hierarchies in the developing and hyper-urbanizing metropolis of Asia, actuating differentiated access to utilities and unjust water trajectories. Critically analysing primary household data from Kolkata (India), the article advocates for specifically designed inclusive water solution strategies to accommodate the most marginalized, namely gender, trans-individuals, and children, inhabiting more vulnerable and unequal (peri)urban spaces such as slums or bastis. In similar vein, Sarkar validates how water crises in a hill city (Shimla) of India should be understood beyond hydrological (erratic rainfall due to climate change) and other physical and socio-economic factors (urban growth and tourism), and as an outcome of infrastructural politics shaping unequal and unjust water conjectures. Sarkar also uses an urban (situated) political ecology approach to read uneven waterscapes of Shimla. The case study argues that "the water crisis, as a context, is dialectical" (p. 1). And thus, in spite of implementation of several hydraulic projects, "…the inherent fissures of inequality within the city that cause differential access to water remain" (p. 1).Inclusive water governance frameworks are key in making low-cost, local technologies work viz. water reuse. Frick-Trzebitzky et al. map the success of an informal municipal partnership engaging a group of interdisciplinary researchers, municipal decision-makers, engineers, and farmers in water reuse in agriculture in Namibia. They investigate complex interplays between human behavioural aspects, functioning of the institutional landscape, and physical-material configurations, and discuss the value of cross-sectoral collaboration in fostering municipal capacities towards efficient water reuse as a sustainable solution in Africa. Koehler et al. examines the knowledge to action framework, investigating interconnections between water politics and policy making, focusing on Kitui County, Kenya. The authors place a provocative proposition for readers to reflect and contemplate: "What if, instead of policy producing practice, practices produce policy?" (p. 11). Documenting detailed insights and recommendations from a knowledge co-production workshop, involving participation of (women) fishers, researchers, fishworkers' forum (partner NGO), and scientists, Ghosh et al. deploy solutionfocused participatory research to capture intersecting social-ecological and socio-hydrological variables in the least explored dried fish sector of the Sundarbans delta.Bhattacharyya et al. reinforce this 'transdisciplinary exigency' (Mukherjee et al. 2022), weaving together cherishable moments of collaborative governance, accommodating agencies of (more-thanhuman) actors on the heritage river the Adi Ganga, flowing through the Kolkata metropolis. The authors apply historical urban political ecology (HUPE) (Mukherjee 2020) to perceive urban riverscapes as adaptive "living systems infrastructure" (Mukherjee 2022), dotted with (a)synchronous space-time movements and flows. Thus, 'solution' is imagined through nuanced interpretations of numerous "(un)successful attempts to revive the river beyond global conceptualizations of what a "river" should be."The diverse range of spatio-empirics across different themes on water-society interactions constituting this issue complexifies 'solutions', conveying its temporal, relational, and political edges, and thus offer
Keywords: Water, Solutions, hydrological, social, Technology, Community, psychological, Adaptive
Received: 31 Jul 2023; Accepted: 03 Nov 2023.
Copyright: © 2023 Mukherjee, Marks, Haeffner, Pande, van Oel, Sanderson and Allen. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY) . The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence: Dr. Jenia Mukherjee, Indian Institute of Technology Kharagpur, Kharagpur, India
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- Published: 11 February 2019
The crisis of water shortage and pollution in Pakistan: risk to public health, biodiversity, and ecosystem
- Ghulam Nabi 1 , 2 ,
- Murad Ali 3 , 4 ,
- Suliman Khan 1 , 2 &
- Sunjeet Kumar 1 , 2
Environmental Science and Pollution Research volume 26 , pages 10443–10445 ( 2019 ) Cite this article
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According to the International Monetary Fund (IMF), Pakistan ranked third among the countries facing severe water shortage. In May 2018, the Pakistan Council of Research in Water Resources (PCRWR) announced that by 2025, there will be very little or no clean water available in the country (Shukla 2018 ). It must be noted that while per capita availability in the 1950s was approximately 5000 m 3 per annum, it has now declined to below 1000 m 3 , which is an internationally recognized threshold of water scarcity (Aziz et al. 2018 ). Currently, only 20% of the country’s population has access to clean drinking water. The remaining 80% populations depends on polluted water primarily contaminated by sewerage (fecal, total coliforms, E. coli colonies), and secondarily by fertilizer, pesticides, and industrial effluents (Daud et al. 2017 ; Sahoutara 2017 ). Such water pollution is responsible for approximately 80% of all diseases and 30% of deaths (Daud et al. 2017 ). In the dried-out pipeline, a single E. coli bacterium can multiply into trillions in just a week (Ebrahim 2017 ), and such pipes are used for the water supply without any treatment. Consuming such polluted waters has not only resulted in the death of several people, but also cause bone and teeth diseases, diarrhea, dysentery, typhoid, hepatitis, cancer, and other waterborne diseases (Daud et al. 2017 ). According to World Health Organization (WHO), waterborne diarrheal diseases are responsible for over 2 million deaths annually across the world, with the majority occurring in children under 5 years (WHO 2018 ).
In Pakistan, approximately 60 million people are at risk of being affected by high concentrations of arsenic in drinking water; the largest mass poisoning in history (Guglielmi 2017 ). Arsenic poisoning can cause cancer, restrictive pulmonary disease, skin lesions, cardiovascular problems, diabetes mellitus, gangrene, neurological impairments, and problems in endocrine glands, immunity, liver, kidney, and bladder as well as socio-economic hazards (Rahman et al. 2018 ). Unfortunately, still, no epidemiological data of arsenic poisoning, alternate drinking water, and health interventions are available to the people at risk.
Taking into consideration the drought-hit deaths of approximately 1832 children in the last 4 years (The Newspaper’s Staff Reporter 2018 ), drying lakes (Ali 2015 ), rivers (Channa 2010 ), lowering water table, excessive use of water, lack of storage mechanism, population explosion, and climatic changes warrant serious attention (Kirby 2018 ). Furthermore, the lack of sound national water policy, lack of federal and provincial government’s interest, water conflict between nuclear-armed Pakistan and India (Kirby 2018 ), deforestation, the overwhelming potential threat to the country’s glacier reserves (Nabi et al. 2017 , 2018 ), and the poor water supply will likely negatively affect agriculture, ecology, and local biodiversity. The wildlife has already entered the red zone (Shaikh 2018 ) and can possibly turn into human crisis with the danger of large-scale regional migration of people due to drought-like situation. We have recommended some suggestions that could possibly help the people of Pakistan to get rid of water shortage and pollution, maintain an ecology, improve agriculture, and conserve local biodiversity.
Sound National Water Policy: An effective National Water Policy and management are needed to conserve and enhance water resources, minimize drinking water pollution, and improve the country’s water supply with proper sewerage facilities.
Switch to bottled drinking water: Although this seems to be an expensive option, but keeping in view the higher concentration of arsenic (50 μg/L) (Guglielmi 2017 ), fecal, bacterial, and other contamination in drinking water (Sahoutara 2017 ), it is time to switch to the bottled drinking water. The polluted water can be used for other household activities. Indirectly, this will also bring the attention of public towards water pollution and conservation.
Building dams: Both large- and small-scale dams are needed, but every effort must be made to minimize their social and ecological cost in terms of population displacement and shock to the existing ecosystem. Hence, small dams having minimal environmental and social cost should be prioritized whose waters can be used for drinking, agriculture, electricity, and fisheries. It will also help in the conservation of aquatic biodiversity and other animals, especially during seasonal migration. Instead of the many dams that are under consideration (Qureshi and Akıntug 2014 ), the authors report that hundreds of small dams can be built in the Khyber Pakhtunkhwa province, which is rich in both aquatic and terrestrial biodiversity and can also possibly help them in conservation by providing habitat and protection from flooding.
Reforestation: Annually, Pakistan loses approximately 2.1% of its forests. If this rate continues, Pakistan will run out of forests within the next 50 years (Randhawa 2017 ). Therefore, reforestation and its management in Pakistan are intensely needed and will help in bringing rain, stabilize climate, temperature, pollution, and siltation. It will also help in controlling recurring floods and will provide suitable habitat for the local biodiversity.
Steam-based car washing: There are hundreds of thousand car washing centers in Pakistan. They not only consume a huge amount of freshwater for cleaning, but also pose a great threat to public health, biodiversity, and ecology by polluting the rivers and environment. Switching to steam-based car washing system will not only conserve the freshwater but will also reduce the water and environmental pollution.
Artificial rain: Like China, Pakistan needs a rainmaking network throughout the country. This will help in solving the problems of water shortage, protecting the ecology, reducing natural disaster, and conserving biodiversity. China is developing the world’s largest weather-manipulating system comprising tens of thousands of fuel-burning chambers. This system will increase rainfall over an area of approximately 1.6 million square kilometers (Chen 2018 ). The friendly relation, and with the execution of China-Pakistan Economic Corridor (CPEC), Pakistan can take advantage to establish this technology in Pakistan.
Trans-boundary level initiatives: Currently, India is damming Pakistani River water which was allocated to Pakistan under the 1960 Indus Waters Treaty with the help of World Bank (News Desk 2018 ). Constructive bilateral discussions can help solve the problem of water shortage and threats to the rivers dependent biodiversity.
Installation of low-cost water filters: The installation of a large number of low-cost water filters throughout the country and especially in polluted areas can provide clean drinkable water to the poor people who cannot afford the expensive bottled water.
Glaciers conservation: Outside the polar region, Pakistan has the highest numbers of glaciers (> 7200) than any other country (Khan 2017 ). Unfortunately, they are melting faster than any other part of the world to an extent that by the year 2035, the country will have no more glaciers (Dawn 2013 ). Furthermore, with the execution of CPEC, humongous quantity of black carbon (Nabi et al. 2017 ) will be blown by the air to the glaciers that will further accelerate melting. Therefore, a national plan for the management of these glaciers is needed. The impact on glaciers can be minimized by allowing only electric vehicles in the nearby highways, providing solar energy systems to the local inhabitants, reforestation, and control over greenhouse gasses.
Restoring lakes. Pakistan has a total of 60 lakes and most of them are highly polluted. Due to pollution, only in Manchar Lake; Asia’s largest freshwater lakes, 14 fish species have become extinct (Ebrahim 2015 ). Restoring these lakes will provide better habitat for the biodiversity, promote ecotourism and agriculture, and water to the lake-dependent.
Regulating tube-wells drilling: Due to increase in population, demand for water increases. Whether it is domestic use, commercial or agriculture, there has been an unregulated use of tube-wells across the country where people extract as much water as they like. Because of this practice, there has been an exponential rise in the number of tube-wells due to which water table is going down in many parts of the country. Therefore, an implementation of strict policy is needed to regulate the number of tube-wells. Furthermore, in the overexploited region, artificial groundwater recharge might help to improve the water table.
Awareness: In Pakistan, water is free and therefore no attention has been given by the public to its conservation. Both on the print and electronic media, awareness is needed for water conservation. Also, as it is practiced in many countries, it is feasible to come up with a realistic water pricing mechanism to discourage its enormous waste both at household level as well as commercial level.
In summary, water scarcity and pollution are serious overwhelming threats to the world’s sixth populous country, Pakistan. The government needs to pay urgent and serious attention to water conservation and minimizing water pollution to avoid serious consequences in the form of drought, famine, internal migration, and loss of biodiversity.
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Institute of Hydrobiology, The Chinese Academy of Sciences, Wuhan, People’s Republic of China
Ghulam Nabi, Suliman Khan & Sunjeet Kumar
University of the Chinese Academy of Sciences, Shijingshan District, Beijing, People’s Republic of China
Department of Management Studies, University of Malakand, Chakdara, Khyber Pakhtunkhwa, Pakistan
German Development Institute, Bonn, Germany
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Correspondence to Ghulam Nabi .
Responsible editor: Philippe Garrigues
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Nabi, G., Ali, M., Khan, S. et al. The crisis of water shortage and pollution in Pakistan: risk to public health, biodiversity, and ecosystem. Environ Sci Pollut Res 26 , 10443–10445 (2019). https://doi.org/10.1007/s11356-019-04483-w
Received : 11 June 2018
Accepted : 05 February 2019
Published : 11 February 2019
Issue Date : 01 April 2019
DOI : https://doi.org/10.1007/s11356-019-04483-w
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Research Paper on Water Crisis
Water crisis research paper:.
According to studies by the World Health Organization, today more than two billion people suffer from water crisis . Experts predict that by 2015 the countries with chronic water shortage will house more than half the world’s population. Fresh water is rapidly becoming a scarce natural resource for in the XX century water consumption increased by 7 times, whereas the world’s population grew only by three times. Lack of water gives rise to a range of economic, social, and political problems that could undermine stability in the world and lead to global shocks.
Research by the United Nations shows that more than half of the planet will either experience serious water shortages or feel its deficit. And by mid-century it already will be three-quarters of the world’s population that will not have enough fresh water.
Experts expect that the deficit will become ubiquitous mainly due to increasing the number of the world’s population. The situation is aggravated by the fact that people are getting richer (which increases their demand for water) and global climate change, which leads to desertification and reduced water availability.
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The main sources of fresh (drinking) water are rivers and freshwater lakes, which are spread extremely uneven. In Europe and Asia, where 70 % of the population is concentrated, there are only 39 % of world reserves of river waters. In Europe, where almost 20 % of the world’s population live, fresh water make up only 7% of all the world’s water.
To reduce the loss of water, it is necessary to carry out a reasonable pricing policy that promotes better water conservation in the residential and industrial sectors. Often people exploit a natural resource, caring little about the losses, if water there is almost for free.
Higher prices also improve the condition of the water delivery systems and reduce its losses. One of the most important consequences of too low prices for water is that insufficient funds are allocated for the development and maintenance of water supply systems. Appropriate services usually do not seek to timely detect the leaks and proceed to actions only after a major incident.
Reasons for the scarcity of fresh water in the world are as follows:
- Intensively increasing water requirements in connection with the growth of the world population.
- The development of economic activities, requiring enormous water resources.
- Freshwater losses due to the reduction of the rivers.
- Water pollution by untreated sewage.
Strengthening the shortage of drinking water and fresh water occurs both because of the increasing number of the world’s population and uncontrolled process of increasing the number of residents of cities. As a result, urban services cannot cope with demand outstripping growth of fresh water.
Use free sample research paper on water crisis to find out the reasons for the water shortage.
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Water Crisis Essay
In this water crisis essay, we had describe about water crisis in details.
Water is the basic requirement for the survival and promotion of humans, animals, birds and vegetation.
Environmental pollution is a major cause of ‘water crisis’ as a result the underground layer increases rapidly.
In 1951, the per capita water availability was about 5177 cubic meters, this has now come down to around 1545 in 2011 (Source: Water Resources Division, TERI).
What is Water Crisis?
The lack of available water resources to meet the demands of water use within a region is called ‘water crisis’.
Around 2.8 billion people living in all continents of the world are affected by water crisis at least one month each year, over 1.2 billion people do not have access to clean water for drinking.
Global Scenario of Water Crisis:
Due to increasing demand for water resources, climate change and population explosion, there is a decrease in water availability.
It is estimated that in the Middle East region of Asia, most of North Africa, Pakistan, Turkey, Afghanistan and Spain, countries are expected to have water stress situation by 2040.
Along with this, many other countries including India, China, Southern Africa, USA and Australia may also face high water stress.
Status of Water Crisis in India – Water Crisis Essay:
In India, 330 million people or nearly a quarter of the country’s population are affected by severe drought due to two consecutive years of weak monsoon.
About 50% of the regions of India are experiencing drought like conditions, particularly in the western and southern states, with severe water crisis.
According to the Composite Water Management Index report released in 2018 by the NITI Aayog , 21 major cities of the country (Delhi, Bangalore, Chennai, Hyderabad) and about 100 million people living in these cities are facing the severe problem of water crisis.
12% of India’s population is already living under ‘Day Zero’ conditions.
Day Zero: In order to attract the attention of all people to limit and manage water consumption in the city of Cape Town, the idea of Day Zero was introduced so as to increase management and awareness of limiting water use.
Causes of Water Crisis in India:
The problems of water crisis in India are mainly indicated in the southern and northwestern parts, the geographical location of these areas that it receives less rainfall, the southwest monsoon does not receive rainfall on the Chennai coast.
Similarly, by reaching the monsoon in the northwest, it becomes weak due to which the amount of rainfall also decreases.
Monsoon uncertainty in India is also a major cause of water crisis. In recent years, due to the impact of El-Nino, rainfall has decreased, due to which a situation of water crisis has arisen.
The agricultural ecology of India is favorable for crops that require more water for production, such as rice, wheat, sugarcane, jute and cotton etc.
The problem of water crisis is particularly prevalent in agricultural areas having these crops, the state of water crisis has arisen due to the strengthening of agriculture in Haryana and Punjab.
Serious efforts are not made to reuse water resources in Indian cities that is why the problem of water crisis in urban areas has reached a worrying situation.
Instead of reusing most of the water in cities, they are directly discharged into a river.
There is a lack of awareness among people about water conservation, the misuse of water is constantly increasing; Lawn, washing of cart, leaving the bottle open at the time of water use, etc.
Efforts to Conserve Water:
Under the Sustainable Development Goal, water availability and sustainable management is to be ensured for all people by the year 2030, the following efforts for water conservation are being made to meet this goal as follows:
At present, the use of low water crops is being encouraged to reduce the excessive use of water due to the intensification of agriculture.
In the Second Green Revolution, emphasis is being placed on low water intensity crops.
Efforts are being made to conserve water through dams, the government is also taking help from the World Bank for dam repair and reconstruction.
Guidelines have been issued by the government for construction of water tanks under the water supply program during the construction of buildings in the cities.
The NITI Aayog has released the overall water management index to inspire the effective use of water in states and union territories.
Precautions to avoid Water Crisis:
High-water crops such as wheat, rice, etc. should be transferred from coarse grains because about one-third of the water can be saved using these crops.
Also, the nutritional level of coarse cereals is also high, the use of low-water crops should be increased in areas with less rainfall.
In recent years, such efforts have been made by the Government of Tamil Nadu, water consumption efficiency should be increased, as it is still less than 30% in the best cases.
Public awareness is essential for water conservation because problem of water crisis has risen, however in some areas of America with less water availability than in countries like India.
SAVE WATER ESSAY | WATER POLLUTION ESSAY | WATER CONSERVATION ESSAY
Conclusion for Water Crisis Essay:
Water is an important natural resource as it maintains all living beings on the earth.
We use it for drinking and cooking, bathing and cleaning, surprisingly less than one percent of the total water supply is potable, but water pollution and misuse of water crisis lead to the ‘water crisis’.
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The world’s road to water scarcity: shortage and stress in the 20th century and pathways towards sustainability
1 Water & Development Research Group (WDRG), Aalto University, Espoo, Finlan, d
J. H. A. Guillaume
2 National Centre for Groundwater Research and Training & Integrated Catchment Assessment and Management Centre, The Fenner School of Environment and Society, The Australian National University, Australia
3 Institute for Environmental Studies (IVM), Vrije Universiteit Amsterdam, Amsterdam, Netherlands
4 Center for Environmental Systems Research (CESR), University of Kassel, Germany
5 Institute of Crop Science and Resource Conservation (INRES), University of Bonn, Germany
T. I. E. Veldkamp
Water scarcity is a rapidly growing concern around the globe, but little is known about how it has developed over time. This study provides a first assessment of continuous sub-national trajectories of blue water consumption, renewable freshwater availability, and water scarcity for the entire 20 th century. Water scarcity is analysed using the fundamental concepts of shortage (impacts due to low availability per capita) and stress (impacts due to high consumption relative to availability) which indicate difficulties in satisfying the needs of a population and overuse of resources respectively. While water consumption increased fourfold within the study period, the population under water scarcity increased from 0.24 billion (14% of global population) in the 1900s to 3.8 billion (58%) in the 2000s. Nearly all sub-national trajectories show an increasing trend in water scarcity. The concept of scarcity trajectory archetypes and shapes is introduced to characterize the historical development of water scarcity and suggest measures for alleviating water scarcity and increasing sustainability. Linking the scarcity trajectories to other datasets may help further deepen understanding of how trajectories relate to historical and future drivers, and hence help tackle these evolving challenges.
The overexploitation of freshwater resources threatens food security and the overall wellbeing of humankind in many parts of the world 1 . The maximum global potential for consumptive freshwater use (i.e. freshwater planetary boundary) 2 , 3 is approaching rapidly 4 , regardless of the estimate used. Due to increasing population pressure, changing water consumption behaviour, and climate change, the challenge of keeping water consumption at sustainable levels is projected to become even more difficult in the near future 5 , 6 .
Although many studies have increased the understanding of current blue water scarcity 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , and how this may increase in the future 5 , 6 , 15 , the historical development of water scarcity is less well understood 10 . Trajectories of these past changes at the global scale could be used to identify patterns of change, to provide a basis for addressing future challenges, and to highlight the similarities and differences in water scarcity problems that humanity shares around the world. This requires crossing scales, performing analyses globally, but at a sub-national resolution. Identifying recurring patterns of change can further provide evidence of key drivers of scarcity and thus help to recognise types of problems and solutions. Understanding what has occurred previously can thus help us to avoid repeating mistakes and to build on past successes.
Like other forms of scarcity, physical blue water scarcity can be fundamentally divided into two aspects: shortage and stress. Water shortage refers to the impact of low water availability per person. In “crowded” conditions, when a large population has to depend on limited resources, the capacity of the resource might become insufficient to satisfy otherwise small marginal demands, such as dilution of pollutants in a water body, and competition may result in disputes 16 . Given a resource and per capita requirements, water shortage can therefore be seen as population-driven scarcity. Water stress refers to the impact of high water use (either withdrawals or consumption) relative to water availability. Use of a large portion of a resource 1 , 13 might lead to difficulties in accessing the resource, including side effects 16 , e.g. social and environmental impacts. Stress can be seen as demand-driven scarcity, potentially occurring even if the population is not large enough to cause shortage.
These two aspects have commonly been assessed in isolation from each other 7 , 10 , despite being combined in the seminal work on water scarcity by Falkenmark 1 , 16 , 17 , as well as some later works 15 , 18 . Indeed, the indicators of water shortage and stress are fundamentally related through per capita water use, and therefore provide a more complete picture when used together:
There are, however, multiple ways each of the terms can be defined, yielding different families of indicators for shortage and stress. For example, use can refer to consumption or withdrawals. Availability might refer to water from different sources, of different quality, or at decadal, annual or seasonal time scales. The population in question might be that which is dependent on a resource, which is physically located within a region, or only that which has access to the resource.
Given the complexity of the impacts, these are clearly crude indicators of actual impacts involved in stress and shortage. There is substantial uncertainty in determining at what value of the stress and shortage indicators, stress and shortage impacts actually occur. Even when justified thresholds are selected, the value of the indicator is typically also reported, so that the reader can form their own opinion of whether stress and shortage have really occurred.
Despite their high level of abstraction, and the multiple ways in which they can be used, the concepts of shortage and stress and their defining indicators are central to understanding the development of scarcity over time. Therefore, they provide an obvious first step in analysing trajectories of past changes.
This paper first explores how water consumption has evolved globally over the entire 20 th century. The analysis uses recently released spatially explicit data for the entire past century on socio-economic development 19 and irrigation 20 , which allow us to assess past water consumption trends in greater detail, using the WaterGAP2 hydrological and water use models 19 , 21 (see Methods). This evolution is put into context by assessment of water scarcity based on the concepts of shortage, stress and per-capita consumption, structured graphically using a Falkenmark matrix 1 , 16 , 17 . Archetypes and shapes of the trajectories are introduced as new concepts to characterize the historical development of water scarcity in regions, and hence to assess the effectiveness of potential alleviation strategies and define pathways towards sustainability.
The version of the shortage and stress indicators we use consider decadal scale water availability and consumption at sub-national scales. They therefore capture the effect of long term sub-national water scarcity, but not the seasonal variation in demand and supply, inter-annual variability or sub-regional variation. We focus on physical blue water scarcity, meaning that issues of access are omitted, and emphasis is on water in lakes, rivers and renewable groundwater rather than “green” water, soil water from precipitation directly used by plants, or non-renewable fossil groundwater. Moderate (high) shortage is deemed to occur when total water availability drops below a requirement of 1700 m 3 cap −1 yr −1 , (1000 m 3 cap −1 yr −1 ) 1 , 7 . Moderate (high) stress is deemed to occur when more than 20% (40%) of available water is consumed 1 . The stress threshold was originally applied to water withdrawals but is used here for water consumption to account for substantial return flows that are still available for downstream users 22 , 23 . The focus on consumption also means that water degradation caused by return flows is not considered as part of stress, though it is still (indirectly) captured through population-driven pollutant load as part of shortage.
This study’s findings show a nearly 16-time increase in population under water scarcity since the 1900s although total population increased only 4-fold over the same time period. Per capita water consumption only shows a slight and irregular increase over the past century, while the expansion of water scarcity is predominantly explained by the effects of spatial distribution of population growth relative to water resources.
The global population has almost quadrupled over the past hundred years, and it reached 6.5 billion in the last time step of the study period, i.e. the 2000s (given decadal results are averages over specified decades, in this case 2001–2010) 24 . Over the same period, annual consumptive blue water use per capita (see Methods for details) increased only from 209 m 3 cap −1 yr −1 in the 1900s (i.e., 1901–1910) to 230 m 3 cap −1 yr −1 in the 2000s, with some variation between decades and a maximum of 256 m 3 cap −1 yr −1 in the 1960s ( Fig. 1B ). The increases in population and per capita water consumption resulted in a total water consumption increase from 358 km 3 yr −1 in the 1900s to 1500 km 3 yr −1 in the 2000s ( Fig. 1B ).
Regional ( A ) and global ( B ) consumptive water use trends over the 20 th century. The filled area represents per capita water consumption trends while the dashed line represents the total water consumption trends. The per capita consumption is divided into different water use sectors. The trend in per capita consumption at the FPU scale is shown as a background. [Adobe Illustrator CS5, ArcGIS 9.2 and Matlab 2015b softwares were used to create the figure; http://www.adobe.com/products/illustrator.html , http://www.esri.com , and http://www.mathworks.com ].
The trends of water consumption over the 20 th century were not, however, similar across the globe ( Fig. 1A ). The consumption per capita seems to have remained rather stable in many regions, such as Southern Africa and South America, but declined in the Middle East (since the 1950s), Northern Africa and South Asia. However, per capita consumption increased rapidly in Australia-Pacific, being over 6-fold greater in the 2000s compared to the 1900s. Increases were also found in Eastern Europe & Central Asia (until the 1990s) and Western Europe, although less rapid.
At the FPU (i.e., food production unit; see Methods) scale, this dataset shows that trends in per capita water consumption also varied significantly within the regions ( Fig. 1A ). A good example is North America, where the west coast experienced a decreasing trend while on the east coast, water consumption per capita increased. Of the world population, 46%, 25% and 29% live in FPUs where per capita consumption respectively increased, decreased, or showed no statistically significant trend over time (two-sided p -value > 0.05 with the Mann-Kendall test).
Although the trend in per capita water consumption varied between regions, total water consumption increased in all regions due to increased population except in Eastern Europe and Central Asia, where the total consumption decreased slightly (~7%) since the collapse of the Soviet Union in 1990 ( Fig. 1A ). Growth was greatest in Australia-Pacific (30-fold increase) followed by Central America, Southern Africa, and Southeast Asia (approximately eight-fold). In a number of regions, consumption increased 3–4 fold, with the lowest increase in Northern Africa with about a three-fold increase.
Globally, irrigation was by far the largest water consumer over the entire study period, with a share ranging over time between 90–94% of global water consumption ( Supplementary Fig. 1B ). It had the largest share in South Asia (96–98%) due to extensive rice cultivation, and in the Middle East (97–99%) due to arid conditions 20 . In Western Europe, the irrigation share of total water consumption was lowest (62–74%), as it includes areas where irrigation is not extensively practiced for food production. Moreover, the economy is more industrialised than, for example, in Asia. Globally, the second largest sector until the 1990s was domestic water consumption. However, this was surpassed by industrial water consumption in the final time step (2000s; domestic 3.7%, industrial 4.3%). A second notable global trend is the emergence of water consumption due to thermal electricity production (~1% share). Regionally, results show larger changes in the shares of different sectors, though the real-world significance of the changes is difficult to judge. In some areas (e.g. Western Europe, Australia/Pacific), the proportion of water consumption used for irrigation has increased and the proportion for domestic consumption has decreased. The opposite has occurred in other areas (e.g. North America, Supplementary Fig. 1A ).
Global and regional water scarcity
Despite only small variations in per capita water consumption over time ( Fig. 1A ), rapidly expanding local populations and increases in total water consumption resulted in a nearly 16-fold overall increase in the population under water scarcity within the 20 th century ( Figs 2 and and 3). 3 ). Whilst in the 1900s just over 200 million people (14% of global population) lived in areas under some degree of water scarcity, this number increased to over two billion by the 1980s (42%), and reached 3.8 billion people (58%) by the 2000s ( Table 1 ; Fig. 2B ).
Regional ( A ) and global ( B ) water scarcity trajectories. Filled graphs represent the absolute population under water scarcity (in billions) while dashed lines represent the population relative to total regional population. M WStr refers to moderate water stress, H WStr to high water stress, M WSh to moderate water shortage, and H WSh to high water shortage. See definitions of these different water scarcity dimensions, and their combinations, in Table 1 and Fig. 4A . [Adobe Illustrator CS5, ArcGIS 9.2 and Matlab 2015b softwares were used to create the figure; http://www.adobe.com/products/illustrator.html , http://www.esri.com , and http://www.mathworks.com ].
Mapped water scarcity categories for years 1905 ( A ), 1935 ( B ), 1965 ( C ), 1985 ( D ), and 2005 ( E ). The definition for each scarcity category is given in Table 1 and Fig. 4A . [Adobe Illustrator CS5 and ArcGIS 9.2 softwares were used to create the figure; http://www.adobe.com/products/illustrator.html , http://www.esri.com ].
M WStr refers to moderate water stress, H WStr to high water stress, M WSh to moderate water shortage and H WSh to high water shortage. See matrix of the scarcity classes in Fig. 4A .
In the 2000s, roughly half of the people under water scarcity suffered either moderate water shortage or moderate water stress ( Table 1 ), while the other half lived in areas facing both water stress and water shortage. Of these, 1.1 billion people (17% of global population) lived in areas facing both high water shortage and high water stress ( Table 1 ; Fig. 2B ). Most of these people lived in South and East Asia, North Africa and Middle East ( Fig. 2A ), with 61–89% of the population under water scarcity. The regions with the lowest proportion of population under water scarcity were Australia-Pacific, South America, North America, and Southeast Asia (7–29%, Fig. 2A ). Around a half of the population under water scarcity in the 2000s suffered water shortage alone, without water stress ( Table 1 ; Fig. 2B ). These areas are located in Sub-Saharan Africa, Central America, Europe, and South and East Asia ( Figs 2A and and3E). 3E ). A small part of the population (2%) suffered water stress alone ( Table 1 ), occurring mostly in North America, Middle East, and Australia ( Fig. 3E ).
A global water scarcity trend-plot ( Fig. 2B ) reveals that the population under water shortage, or a combination of high water stress and water shortage, has increased rapidly since the 1960s, while water stress alone has remained rather low over the entire study period. There are, however, differences in regional trajectories ( Fig. 2A ), indicating that, for example, in the Middle East, Northern Africa and North America, scarcity has developed gradually over the whole study period while in many other regions (e.g. Central America, Southern Africa, South Asia, Southeast Asia, and East Asia) there has been a steep increase in scarcity trend since the 1960s.
Different FPUs show distinct population dynamics, climate patterns, and developments of water consumption per capita. An FPU’s long-term water scarcity trajectory over time is visualised using the Falkenmark matrix 16 ( Fig. 4 ) that distinguishes between population-driven water shortage and demand-driven water stress, and highlights the relationship with per capita consumption using superimposed diagonal lines. Drivers and adaptation strategies are strongly dependent on the level and type of water scarcity an FPU is experiencing ( Fig. 4B ). As defined in Table 2 and discussed below, the notions of archetypes and shapes help to make sense of these trajectories. The archetype refers to the positioning within the Falkenmark matrix ( Fig. 5 ), whilst shape ( Fig. 6 ) refers to the direction of change over time.
( A ) the water scarcity categories; and ( B ) Drivers and alleviation measures. The diagonal lines in tile B refer to per capita consumption isolines. [Adobe Illustrator CS5 –software was used to create the figure; http://www.adobe.com/products/illustrator.html ].
FPU water scarcity trajectories by scarcity archetypes in a map ( A ) and within the Falkenmark matrix ( B–G ). Archetypes categorise FPUs according to their water scarcity status (corresponding to position on the plot) and where both shortage and stress occur, according to which occurs first (which is related to the level of per capita consumption). The trajectories are grouped based on irrigation zone 20 they are located in. See Table 2A for definitions and Supplementary Table 2 for percentage of population in each archetype – irrigation zone combination. Note: only FPUs with more than one million people are included. [Adobe Illustrator CS5 and R studio softwares were used to create the figure; http://www.adobe.com/products/illustrator.html , https://www.rstudio.com ].
( A and B ) FPU shapes shown as map, separated according to whether scarcity has been experienced ( B ) or not ( A ). ( C ) Examples of shapes of FPU water scarcity trajectories. The diagonal lines refer to per capita consumption isolines and numbers to FPUs (location indicated in tile B ). See Table 2B for definition of each shape category and Supplementary Fig. 2 for each FPU trajectory categorised by their shape. [Adobe Illustrator CS5 and R studio softwares were used to create the figure; http://www.adobe.com/products/illustrator.html , https://www.rstudio.com ].
* Trajectories are characterised in two different ways.
+ Trajectories are assigned to the first applicable category.
FPU water scarcity trajectories: archetypes
The concept of water scarcity trajectory archetypes captures issues related to water scarcity status and per capita consumption. Trajectory archetypes are thus also useful to identify possible adaptation measures in an FPU. Their definitions are summarised in Table 2A while Fig. 5 maps the regions belonging to each archetype, and displays their trajectories. Each archetype is discussed further below.
The archetypes stress alone or stress first (before shortage) are experienced if per capita consumption is high ( Fig. 5F,G ), such that scarcity is demand-driven. FPUs in this category would thus benefit most from demand-side oriented adaptation strategies. The archetypes shortage alone or shortage first ( Fig. 5C,D ) are experienced if per capita consumption is low, such that scarcity is population-driven. This calls for supply-side adaptation strategies in particular. This division of adaptation strategies also corresponds to a distinction between ‘soft’ behaviour-change and ‘hard’ infrastructure-based solutions, respectively 1 , 17 , 25 , 26 ( Supplementary Table 1 ).
Specifically, using a threshold of stress of 20% and a per capita water availability (shortage) threshold of 1700 m 3 cap −1 yr −1 , the switch-over point between stress first and shortage first occurs at a per capita consumption of 340 m 3 cap −1 yr −1 ( Fig. 5A–F ; Methods). The stress and shortage at same time archetype is a borderline case, in which per capita consumption varies near that switch-over point. For that archetype, both adaptation strategies may be relevant. When an FPU is of a no scarcity archetype, no direct adaptation measures are necessary. However, as population grows, the per capita consumption of an FPU sets it on a trajectory towards either stress first or shortage first, and so the above introduced guidelines may apply.
For stress first and stress alone archetypes, the need for demand management rather than supply side measures 1 is motivated by the common ideological point of view that high per capita water consumption should be reduced. In practice, however, there seems to be a tendency to meet demand first, for example in the case of trajectories with a constant per capita demand shape (see Fig. 6C ). This might be explained in terms of the “hydraulic mission” 27 , common around the world in the 20 th century, which aims to dominate nature in order to increase food production and provide water and food security. This has to some extent been curbed by increased emphasis on social and environmental impact assessment 27 , 28 . Ideally, adaptation strategies should focus first on increasing water productivity (domestic, agricultural, and industrial) or on shifting to lower water footprint goods and services. The latter might include reducing virtual water exports 29 and/or increasing virtual water imports 30 . Several of these actions would not be captured by the data and analysis applied, and may have already occurred, as suggested by recent studies 29 , 31 , 32 , 33 , 34 .
For cases where shortage occurs before stress, supply-side options are in principle preferred because lower per capita water consumption provides less potential for demand-side intervention than when stress occurs first. There are, however, two main ways to handle water shortage: (i) increasing available water, or (ii) limiting population. Available water can be increased by using desalination (in coastal areas) 35 , introducing physical water transfers 36 , 37 and/or reducing non-productive evaporation 38 . Increased storage capacity is likely to play a smaller role at decadal scale, but is a common strategy to increase seasonal or inter-annual water availability. Emigration and lowered birth rates may limit population, but are perhaps better treated as side-effects of other developments rather than explicit water scarcity strategies. Moreover, an area can adapt to water shortage by using the strategies to reduce per capita water consumption. Possibilities for reducing water requirements include more efficient irrigation 39 , reduction of food losses 40 , reduction of water-intensive goods 41 , 42 , and reduction of leakages in public supply systems 43 .
The potential for reducing blue water consumption notably depends on green water availability (soil water from precipitation), especially in the case of agriculture 13 , but also, for example, on urban parks and golf courses. Areas with reliable green water resources tend to have lower blue water consumption, and hence less stress. While this study does not quantify green water availability, it does show that different archetypes occur depending on the reason for irrigation consumption (which is the largest water-consumption sector in most areas). As discussed in Siebert et al . 20 , irrigation is notably driven by: (i) the desire to make agriculture possible in arid areas; (ii) the desire to increase productivity in semi-arid and temperate areas; or (iii) weed-suppression by controlling the water level when growing rice. The results by irrigation zones 20 (see Fig. 5 for trajectories by irrigation zones, and tabulated results for population in Supplementary Table 2 ) indicate, for example, that most of the high per capita consumption stress first (90% of FPUs within those archetypes) or stress alone (82% of FPUs) trajectories occur in arid regions, consistent with higher crop water requirements due to irrigation. Shortage alone in turn occurs commonly in wet areas (50% of FPUs), consistent with low water requirements and high population pressure.
In practice, it appears that shortage is not directly tackled until stress occurs. Moderate shortage is tolerated, perhaps buffered by low consumption and other water sources, such as virtual water imports, green water and fossil groundwater. This avoids tackling the underlying issue of population growth, and stress is reached some time later. For example, in North-eastern Mainland China, some FPUs have experienced shortage since before 1905, and others more recently since 1925 and 1975 ( Supplementary Fig. 3 ). Stress followed years or decades later, as population grew. Groundwater and a number of inter-basin transfers are already in use, and additional south-north transfers are in development 44 , 45 . These FPUs are good examples where per capita blue water consumption is low enough that shortage occurred first. There is, however, significant potential for further reductions due to large virtual water exports, which could avoid the need for inter-basin transfers 45 .
FPU water scarcity trajectories: shapes
When FPU trajectories are distinguished by their shape , it is possible to understand the dynamics of consumption over time, and how that has impacted on the scarcity type (shapes are summarised in Table 2B ; example trajectories for each shape are shown in Fig. 6C and all trajectories in Supplementary Fig. 2 ). Further, shapes can be used to assess what needs to be done for an FPU to be put on a sustainable pathway, avoiding both water stress and water shortage in the long term. The majority of FPUs show significant temporal variation in per capita water consumption, stress, and shortage, consistent with the expected tension between population growth, water supply and demand management. In general, achieving sustainable water consumption on a decadal scale requires a combination of stabilising population, enforcing limits of sustainable supply, mitigating impacts of water stress and/or reducing water requirements.
All these strategies are likely to be required to deal with FPUs in the shape categories increasing scarcity and other . The former face both incessant population growth and intensification of water consumption, which currently leads to strictly increasing stress and shortage (6.6% of global population in 2000s, Fig. 6 ), for example in parts of the Balkans (FPU 169, Fig. 6 ). The other shape category (32.2% of the population) shows complex trajectories for which specific recommendations cannot be made without other economic or demographic data.
In FPUs where the trajectory shape is determined by constant per capita demand (29% of population), changes in scarcity are predominantly determined by population growth. Constant per capita demand is visible as a (relatively) straight diagonal trajectory in the Falkenmark matrix ( Figs 4B and 6C ). As long as per capita consumption is kept in check, stabilising population is an effective strategy for FPUs with any trajectory shape as it avoids increases in shortage and total consumption, and hence stress.
In FPUs with strictly increasing stress but varying shortage (4.9% of population), consistent intensification of water consumption is the key concern, for example in northern France (FPU 121, Fig. 6 ). Recognising the socio-economic importance of exploitation of the local water resource and potential difficulty in curbing water consumption, achieving sustainability may involve mitigation measures to allow greater water consumption than would otherwise be possible. Examples include improving water allocation and other governance mechanisms, providing storage and channelling engineering works, optimising environmental flows, and benefit-sharing to compensate other impacted users. This corresponds to the idea of ‘decoupling’ growth from impacts 46 .
In FPUs with strictly increasing shortage but varying stress (15% of population), the key concern is strong population growth, as in northern India (FPU 494, Fig. 6 ). Recognising that addressing the drivers of population growth may take time, achieving sustainability may involve reducing local water requirements, so that consumption does not grow in parallel with population. This corresponds to decoupling growth from resource use and may be achieved by improved water productivity or decreasing water-dependent production 40 , 41 . Decoupling from resource use already appears to be occurring in many areas, as shown by decreasing trends for per capita consumption ( Fig. 1 ). In FPUs where irrigation is important, per capita consumption is particularly influenced by area equipped for irrigation and a combination of irrigation efficiency and climate effects. However, the most prominent examples of decoupling from local resource use are FPUs dominated by cities, taking as an example FPU 307 in western Africa (32 million people in 2000s), which includes the megacity of Lagos in Nigeria. While some food and other water-dependent products are produced in the hinterland, they can also be imported from elsewhere (along with virtual water) 47 . Such areas can therefore have relatively low local blue water requirements, mainly for domestic and industrial water supply (83% of total water consumption at FPU 307). The sustainability of such FPUs depends largely on their interactions with regional and global water resources.
In addition to cases where trends suggest that decoupling is occurring, the analysis identifies some cases with a stress decrease -shape (10% of population), or where stress stabilised ( stress ceiling -shape, 2% of population). In most cases, this occurs as a result of decreases in consumption, but appears to be driven often by socio-economic factors rather than limited water availability. Results show that FPUs that have reached a stress ceiling are mostly those with high per capita consumption that suffer water stress alone ( cf. Figs 3 and and6B) 6B ) in North America, Central Asia, or Africa. However, stress ceilings occur even with a stress level of 10% (e.g. in Northern Africa), and decreases in stress in FPUs that are not water scarce in large parts of the former Soviet Union ( Fig. 6A ), following the dissolution of the Soviet Union. This may thus be related to the region’s political and economic changes. Consistent with the idea of a “hydraulic mission” 27 , 28 , dams and canals increased supply to allow irrigation demand to expand. Reductions in consumption then occurred not just due to improvements in irrigation efficiency but also due to a shift from exported cotton (and virtual water 29 ) to food self-sufficiency in the newly independent nation states 48 , 49 . Water scarcity trajectories and their sustainability are closely tied with other socio-economic and political issues.
This study highlights key issues in understanding global historical water scarcity and pathways for future adaptation. Considering both forms of water scarcity, this analysis provides an improved understanding of blue water consumption and trajectories of past water scarcity development globally at sub-national level for the entire 20 th century. The results show that more people are under water scarcity than previously estimated ( Supplementary Table 4 ).
Only a few previous studies assessed historical water scarcity using multiple water use sectors 10 , 19 , 50 , and even then only for the past 50 years. This study’s results compare well with previous trends and estimates of water consumption since 1960, the starting period of existing assessments 10 , 50 ( Supplementary Table 3 ). The largest improvement in this study, in terms of water consumption trends, is the use of historical spatially explicit irrigation maps 20 rather than national values. This results in large differences in the location and extent of irrigation areas, particularly in large countries, such as the USA 20 .
Findings for population under stress and shortage separately also show good agreement with existing studies of historical water scarcity ( Supplementary Table 4 ). The existing studies focus on water stress alone 10 or water shortage alone 7 , or assess both forms of scarcity at only one or two time steps 16 or scenarios 29 , with the exception of one study 18 that assesses the interannual variability of blue water scarcity. Assessing both shortage and stress over several decades provides additional insights on the development of water scarcity. The FPU-level trajectories show signs not just of differences in resource endowments and local history, but also similarities due to shared problems and diffusion of solutions, suggestive of a global shared destiny for which collaboration is essential. Classifying sub-national water scarcity trajectories in terms of archetypes ( Fig. 5 ) helps to highlight possible adaptation actions to cope with shortage and/or stress, depending on the level of water consumption in per capita terms. Classifying trajectories in terms of their shape ( Fig. 6 ) helps to highlight different approaches to put FPUs on a sustainable pathway. Nearly all FPUs show an increase in scarcity over time as population increases ( Fig. 6 ; Supplementary Fig. 2 ), indicating that understanding of scarcity adaptation actions and pathways to sustainability will only become more important in the future. These historical trajectories provide a common foundation from which further work can dig deeper to identify mistakes to avoid repeating, and past successes worth replicating, in order to better tackle future challenges of water scarcity.
As noted in Introduction, results presented correspond to a well-defined scope focussed on scarcity associated with a long-term view of consumptive blue water use. The selected indicators are widely adopted and can be linked to previous studies 8 , 9 , 10 , 14 , 18 . Additional information sources that would allow more sophisticated water scarcity analysis are not available for the entire study period. These include water quality, technological and social access to water and trade of virtual water. Future studies could include these aspects.
Furthermore, the analysis is commensurate with the significant uncertainty involved in the datasets and models used to cover the globe for the past 110 years 51 , 52 . In this study, two important datasets are combined: water availability and water use, both provided by the WaterGAP2 model. In order to reduce uncertainty in water availability estimates, the model has been calibrated in a basin-specific manner against mean annual river discharge using 1319 gauging stations 53 . Previous studies have reported that the model performs well in relation to other global hydrological models when compared to observations 51 , giving confidence in our water availability estimates. Water use data, on the other hand, is viewed as particularly uncertain 54 . For example, in a multi-model comparison, Wada et al . 55 show that modelled irrigation demand compares reasonably well to country-scale reported values (deviations in the range of +/− 15% in most cases) and conclude that most models are capable of simulating regional variability in irrigation water demand across the globe. Since irrigation constitutes the largest share to global total water consumption and is the dominant water-consuming sector in many parts of the world, it is very likely to also dominate the uncertainty in estimated total water consumption.
We compared the water consumption data of this study to two previous studies assessing the past water consumption 10 , 50 ( Supplementary Table 3 ), and found that the consumption estimates vary on the order of 35%, this study being the most conservative one. When our water scarcity results were compared to existing studies 10 , 18 ( Supplementary Table S4 ), we found that estimates of global population under shortage, and population under stress vary on the order of 15% and 30% respectively.
Besides these two key input data products, various assumptions have been made in the analysis itself. A notable assumption relates to the thresholds used to differentiate different states of water stress and shortage. Whilst these assumed thresholds directly affect the amount of population living under water scarcity, they do not affect the trajectory lines in the Falkenmark matrix themselves. Correspondingly, the shapes of the trajectories are not affected by these thresholds. However, trajectory archetypes would somewhat be impacted, as changing these thresholds would mean a specific FPU reaches a certain level of scarcity a decade earlier or later.
As a result, our emphasis is on drawing coherent insights rather than providing precise estimates. In this context, specific numbers represent one possible realisation in the context of significant uncertainty. This is important when comparing our results for a specific year with other studies. The key conclusions of this study are, however, robust, namely the interpretation of sub-national shortage and stress trajectories and the importance of population growth and per capita water consumption in determining local development of scarcity. They are consistent with existing understanding, and strongly influenced by patterns in input data (e.g. population growth and expansion of irrigation area) that are independent of other assumptions made in the analyses.
The analytical approach used and the initial insights it provides could also be used as a foundation for further research. Additional information about uncertainty could be obtained by systematically repeating the analysis with other models and forcing datasets, as has been done in comparable contexts 5 . This would, however, require a carefully chosen, meaningful set of scenarios. A range of different assumptions can be used regarding scarcity thresholds and indicators, focussing on different issues delimiting different perspectives on safe and just operating spaces for socio-ecological systems 3 , 56 . Calculating indicators at seasonal 11 , 57 or annual scale 18 , 58 would allow investigation of how shortage and stress occur at shorter time scales, more closely related to every-day operations rather than long-term planning. Ideally, availability would be tied to access, which would help alleviate problems related to selection of spatial scale 59 . Focussing on water quality 60 , 61 , unsustainable water sources 62 , and on spatially explicit environmental flow requirements 4 , 63 (the thresholds used for water stress assume global environmental flow requirements of 30% 17 ) would explicitly identify the portion of available water that should not be used to avoid stress according to different criteria. Similarly, focussing on self-sufficiency of water and food 12 , 58 , 64 would identify specific water requirements for shortage, though it would also require greater consideration of both blue and green water 13 .
Whether self-sufficiency is required is particularly relevant in the context of trade 65 and virtual water transfers 31 , which are not captured in this study. From an economics perspective, scarcity is not intrinsically problematic, but rather raises questions of optimal allocation of the scarce resources, trade to make use of comparative advantages, and the inclusion of externalities. Prominent issues include the role of water quality and safety 66 , and accessibility and equity determined by social, economic and political circumstances 25 , 67 , 68 , 69 , 70 , 71 . Linking the trajectories to other datasets may help deepen understanding, expanding and better explaining the shapes introduced here ( Table 2B ), and how they relate to historical and future drivers as well as limits to adaptation.
Analysis unit: Food production units
This study used food production units (FPUs), a combination of river basin and administrative boundaries 7 , 72 , 73 , as an analysis unit. These are reported to be suitable for water scarcity studies 7 , 58 . For this project, a set of FPUs were developed that are consistent with the basin delineation of the WaterGAP2 hydrological and water use models, resulting in 548 FPUs. It is important to use the same delineation for FPUs as watersheds of the WaterGAP2 model, as the way water availability is dealt with (see Fig. 7 ) requires that FPUs do not cross the borders of large river basins. Results are also aggregated from the FPU scale to regional ( n = 12) scale. The regions are based on UN macro regions aggregating the countries to larger units 74 with the difference that some of the largest regions were divided into smaller regions by Kummu et al . 7 to be more suitable for (historical) water analyses.
Water availability calculations in a large basin with several FPUs, i.e. each FPU is a sub-basin for the large basin. A: schematic illustration of a basin with four FPUs; B: Runoff of each grid cell in km 3 yr −1 ; and C: discharge of each grid cell in km 3 yr −1 . The share of available water resources is calculated as the sum of discharges of each grid cell within an SBA divided by the sum of discharges of all grid cells within a basin. The available water resources are then calculated by multiplying that share with the total available runoff of the whole basin. [Adobe Illustrator CS5 –software was used to create the figure; http://www.adobe.com/products/illustrator.html ]
This analysis used the global hydrological model WaterGAP2 53 to derive gridded estimates for runoff and river discharge at 30 arc-min spatial resolution for the study period of 1901–2010. Based on daily meteorological forcing fields and spatially distributed physiographic information (e.g. soil, land cover), the model simulates the terrestrial water cycle by a sequence of storage equations for the storage compartments canopy, snowpack, soil, renewable groundwater, and surface water bodies. For this study, simulations were driven by WATCH Forcing Data (WFD) which is available for the period 1901–2001 75 . Since it is not recommended to combine WFD with other similar data-sets 53 , 76 in order to derive full coverage over the study period 1901–2010, simulations for the period beyond the year 2001 were based on 1990s climate forcing.
Since this analysis focuses on long-term trends in water scarcity, the 10-yr annual average over each decade was calculated for both discharge and runoff to compensate for inter-annual variability. These data were then used to assess the water availability in each FPU. The calculation of water availability can be divided into two cases:
- In cases when an FPU consisted of one basin or several small basins, water availability was simply the sum of annual runoff generated within the area of a specific FPU.
- In cases of large river basins that were divided into several FPUs, a simple ‘water sharing rule’ was used to assign the available freshwater resources within each FPU 5 , 12 . This was developed in a way that it would be usable for both water shortage and water stress calculations, i.e. the sum of water availability of the FPUs within the basin cannot exceed the annual runoff of the basin. The water sharing rule was based on a discharge proportion of FPUs within a basin multiplied with the annual runoff, as illustrated in Fig. 7 .
The water use model of WaterGAP2 simulates water withdrawals and consumption of the following sectors: i) irrigation, ii) livestock farming, iii) thermal electricity production, iv) manufacturing industries, and v) households and small businesses (domestic).
To indicate the area equipped for irrigation (AEI), the analysis used the HID product by Siebert et al . 20 , which gives spatially explicit AEI for the entire 20 th century. The proportion of irrigated harvested rice area was based on the MIRCA-2000 dataset 77 . The proportions were kept at year 2000 level throughout the study period due to lack of historical data. As in the case of the water availability simulations (see above), to simulate the irrigation water consumption beyond 2001, climate forcing data from the 1990s were used. The estimate of consumption for the 2000s should therefore not be included when assessing trend in per capita consumption. Irrigation water consumption is the amount of water that must be applied to the crops by irrigation in order to achieve optimal crop growth. Monthly consumptive irrigation requirements are therefore based on climate, the spatial extent of AEI and crop type (rice and non-rice). Return flows, i.e. water withdrawal minus water consumption, which account for water that infiltrates and returns to the water cycle, are not quantified in this study.
Livestock water consumption was calculated on the basis of gridded information on the number of livestock units and water consumption per head and year, taking into account 10 livestock types 21 . Due to limited data prior to the year 1960, livestock water consumption for the period of 1900–1960 was kept at the level of 1960. Overall, this may lead to an underestimation or overestimation in livestock water consumption depending on the FPU 78 , which is expected to be minor as the amount of livestock water consumption is small compared to the other sectors. Water consumption estimates for electricity, manufacturing, and domestic sectors were based on the methodologies described in Flörke et al . 19 . In brief, domestic water consumption is estimated from population and domestic water use intensity, taking into account structural and technological changes. Country-scale water consumption in the manufacturing sector is calculated from manufacturing structural water use intensity, gross value added, and consumption coefficients; again taking into account technological change. The amount of water withdrawn and consumed for cooling purposes in thermoelectric power production is determined from the annual thermal electricity production and the water use intensity of each power station, distinguishing three cooling system types (once-through, pond, and tower cooling systems) and several fuel types (fossil/biomass/waste-fuelled, nuclear, natural gas/oil combined, coal/petroleum residuum-fuelled). Based on this information, the model approach distinguishes 14 combinations of plant type (PT) and cooling system (CS). In 2010, about 2.8% of cooling water abstractions evaporated, i.e. most of the water withdrawn was discharged back into rivers (Flörke et al . 19 ).
To get the total water consumption, all the water use sectors are summed together. Trends in per capita consumption (see background in Fig. 1A ) were determined with the Mann-Kendall test, calculating the Kendall correlation of demand with time. A p -value of 0.05 was used as part of a two-sided test of whether the correlation was statistically significantly different from zero.
Water stress calculations
The indicator of blue water stress is the water use to availability ratio. We use consumption rather than withdrawals, such that water ‘use’ means that water is no longer available for other users. The indicator was calculated for each decade and for each FPU. The water stress thresholds used are, however, those for the withdrawal-based water stress index (WSI) developed by Falkenmark 16 , and used by a number of other studies 8 , 10 , 57 , 78 :
- WSI <0.2: no water stress
- WSI = 0.2–0.4: moderate water stress
- WSI >0.4: high water stress
Using withdrawals risks over-estimating the actual stress as a substantial part of the withdrawals are available for downstream users as return flows 22 , 23 . On the other hand, using water consumption, as in this study, might underestimate the water stress. Recent work by Munia et al . 79 uses consumption and withdrawals as minimum and maximum levels of scarcity, respectively. They show that the difference between these two estimates results in an 18 percent point difference in the amount of population under water stress. Similar uncertainties in the absolute amount of people under water scarcity should be considered for the numbers quoted in this study. This may also be worthwhile approach for future work. Finally, it should be stressed that the thresholds used assume a global environmental flow requirements of 30% 17 .
Water shortage calculations
For water shortage calculations the analysis is based the water crowding index (WCI) developed by Falkenmark 17 , 80 . WCI is calculated by dividing the water availability by total population of an FPU. Here, historical, spatially explicit, population data is from HYDE 3.1 81 . The water shortage thresholds are as follows:
- WCI >1700 m 3 cap −1 yr −1 : no water shortage
- WCI = 1000–1700 m 3 cap −1 yr −1 : moderate water shortage
- WCI <1000 m 3 cap −1 yr −1 : high water shortage
Water scarcity matrix and related calculations
To illustrate the combination of water stress and water shortage, the analysis used the Falkenmark water scarcity matrix ( Fig. 4 ). By plotting water stress against shortage over time, water scarcity trajectories were derived for each FPU. These trajectories in turn were categorised for archetypes and shapes ( Table 2 , and see below).
The formulas used for the indicators mean that for any combination of stress and shortage, per capita consumption can also be calculated (see diagonal lines in Fig. 4B ). For example, consider the point where an FPU is classified as under both water stress and water shortage:
The corresponding per capita consumption can be calculated for those values of stress and shortage (see also Fig. 4B ):
For a given per capita consumption, this formula can be rearranged to identify whether an FPU would already be stressed when the shortage threshold is reached (shortage = 1700 m 3 cap −1 yr −1 ).
Therefore, the following interpretation can be made when assuming shortage of 1700 m 3 cap −1 yr −1 :
If per capita consumption = 340 m 3 cap −1 yr −1 → stress = 0.2 (stress and shortage same time)
If per capita consumption >340 m 3 cap −1 yr −1 → stress >0.2 (stress occurs first)
If per capita consumption <340 m 3 cap −1 yr −1 → stress <0.2 (shortage occurred first)
The scarcity archetypes define the water scarcity status and level of per capita consumption (see Table 2A ). Scarcity categorisation for archetypes is based on the lowest stress (20%) and shortage thresholds (1700 m 3 cap −1 yr −1 ). ‘No scarcity yet’ are FPUs that have never reached the lowest threshold of water stress (20%) or shortage (1700 m 3 cap −1 yr −1 ). For ‘Shortage alone’, water availability has passed the threshold of 1700 m 3 cap −1 yr −1 , but stress has remained below the threshold of 20%. ‘Stress alone’ occurs where stress exceeds 20% but water availability (i.e. shortage) has never dropped below 1700 m 3 cap −1 yr −1 . ‘Stress first’, ‘Shortage first’ and ‘Stress and shortage at same time’ occur when the trajectory has exceeded both the stress and shortage thresholds, sub-categorised according to which type of strategy is reached first.
The scarcity shapes, in turn, divide the trajectories into categories based on their shape when plotted in the Falkenmark matrix. Specific rules for each shape were developed as outlined in Table 2B .
How to cite this article : Kummu, M. et al . The world’s road to water scarcity: shortage and stress in the 20th century and pathways towards sustainability. Sci. Rep. 6 , 38495; doi: 10.1038/srep38495 (2016).
Publisher's note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Study was funded by Academy of Finland project SCART (grant no. 267463), Emil Aaltonen foundation (‘eat-less-water’ project), Academy of Finland funded SRC project ‘Winland’, and Maa- ja vesitekniikan tuki ry . Additionally, P.J. Ward received funding from the Netherlands Organisation for Scientific Research (NWO) in the form of a VENI grant (grant no. 863-11-011) and T.I.E. Veldkamp from EU 7th Framework Programme through the projects ENHANCE (grant agreement no. 308438) and EartH2Observe (grant agreement no. 603608). Authors are grateful to Suvi Sojamo and Olli Varis for their comments and support.
Author Contributions M.K., J.H.A.G., H.d.M., S.E., S.S. and P.J.W. designed this study in consultation with M.F. and T.I.E.V. The modelling was conducted by S.E. and M.F. supported by M.K., J.H.A.G., H.d.M. and M.P. Analyses were conducted by H.d.M., J.H.A.G. and M.K. in consultation with S.E., S.S. and P.J.W. Statistical analyses for trajectory classification were conducted by J.H.A.G. M.K., J.H.A.G., S.E. and T.I.E.V. wrote the article, with contributions from all co-authors.
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