Water scarcity threatens people in various regions, and has predominantly been studied from a water quantity perspective only. Here we show that global water scarcity is driven by both water quantity ...and water quality issues, and quantify expansions in clean water technologies (i.e. desalination and treated wastewater reuse) to 'reduce the number of people suffering from water scarcity' as urgently required by UN's Sustainable Development Goal 6. Including water quality (i.e. water temperature, salinity, organic pollution and nutrients) contributes to an increase in percentage of world's population currently suffering from severe water scarcity from an annual average of 30% (22%-35% monthly range; water quantity only) to 40% (31%-46%; both water quantity and quality). Water quality impacts are in particular high in severe water scarcity regions, such as in eastern China and India. In these regions, excessive sectoral water withdrawals do not only contribute to water scarcity from a water quantity perspective, but polluted return flows degrade water quality, exacerbating water scarcity. We show that expanding desalination (from 2.9 to 13.6 billion m3 month−1) and treated wastewater uses (from 1.6 to 4.0 billion m3 month−1) can strongly reduce water scarcity levels and the number of people affected, especially in Asia, although the side effects (e.g. brine, energy demand, economic costs) must be considered. The presented results have potential for follow-up integrated analyses accounting for technical and economic constraints of expanding desalination and treated wastewater reuse across the world.
► Simulated 60-year time series of domestic, manufacturing, and thermoelectric water use. ► Global domestic water use has continuously increased driven by growing population and rising prosperity. ► ...Transformation processes and policy regulations have slowed down and reduced global domestic and industrial water uses. ► Our results imply that the maximum of global water withdrawals has not been reached yet. ► To reach the MDGs, secure water supply and reduction of untreated wastewater are among the most important actions to be undertaken.
To enhance global water use assessment, the WaterGAP3 model was improved for back-calculating domestic, manufacturing and thermoelectric water uses until 1950 for 177 countries. Model simulations were carried-out on a national scale to estimate water withdrawals and consumption as well as cooling water required for industrial processes and electricity production. Additionally, the amount of treated and untreated wastewater as generated by the domestic and manufacturing sectors was modeled. In the view of data availability, model simulations are based on key socio-economic driving forces and thermal electricity production. Technological change rates were derived from statistical records in order to consider developments in water use efficiency, which turned out to have a crucial role in water use dynamics. Simulated domestic and industrial water uses increased from ca. 300km3 in 1950 to 1345km3 in 2010, 12% of which were consumed and 88% of which were discharged back into freshwater bodies. The amount of domestic and manufacturing wastewater increased considerably over the last decade, but only half of it was untreated. The downscaling of the untreated wastewater volume to river basin scale indicates a matter of concern in East and Southeast Asia, Northern Africa, and Eastern and Southern Europe. In order to reach the Millennium Development Goals, securing water supply and the reduction of untreated wastewater discharges should be amongst the priority actions to be undertaken. Population growth and increased prosperity have led to increasing water demands. However, societal and political transformation processes as well as policy regulations resulting in new water-saving technologies and improvements counteract this development by slowing down and even reducing global domestic and industrial water uses.
Information on fecal coliform (FC) concentrations in European rivers is scarce. The objective of this study was to identify hotspots of water pollution in Europe and provide information on the ...different FC sources and their contributions to the loads that lead to concentrations in rivers. Model simulations were carried-out with the large-scale water quality model WorldQual to assess the calculated loads regarding to its associated sources and to further estimate the related in-stream concentration. For the year 1995, model results indicated that FC loadings were higher in central Europe with 500 to above 2000 1010 cfu km−2 a−1 than in northern and eastern Europe where loadings ranged between 0 and 200 1010 cfu km−2 a−1. Major sources of FC loadings are domestic sewage, followed by scattered settlements (private treatment), urban surface runoff and manure application. Concentrations showed similar regional patterns as loadings, with high concentrations in central Europe and low concentrations in northern and eastern Europe.
•We model fecal coliform loadings and in-stream concentrations in European rivers.•The domestic sector is the main contributor to fecal coliform loadings.•The regional patterns of loadings and in-stream concentrations are similar.•Hotspots of fecal coliform in-stream concentrations are located in central Europe.
Due to the increasing relevance of analyzing water consumption along product life cycles, the water accounting and vulnerability evaluation model (WAVE) has been updated and methodologically ...enhanced. Recent data from the atmospheric moisture tracking model WAM2-layers is used to update the basin internal evaporation recycling (BIER) ratio, which denotes atmospheric moisture recycling within drainage basins. Potential local impacts resulting from water consumption are quantified by means of the water deprivation index (WDI). Based on the hydrological model WaterGAP3, WDI is updated and methodologically refined to express a basin’s vulnerability to freshwater deprivation resulting from the relative scarcity and absolute shortage of water. Compared to the predecessor version, BIER and WDI are provided on an increased spatial and temporal (monthly) resolution. Differences compared to annual averages are relevant in semiarid and arid basins characterized by a high seasonal variation of water consumption and availability. In order to support applicability in water footprinting and life cycle assessment, BIER and WDI are combined to an integrated WAVE+ factor, which is provided on different temporal and spatial resolutions. The applicability of the WAVE+ method is proven in a case study on sugar cane, and results are compared to those obtained by other impact assessment methods.
Water scarcity has become a major constraint to socio‐economic development and a threat to livelihood in increasing parts of the world. Since the late 1980s, water scarcity research has attracted ...much political and public attention. We here review a variety of indicators that have been developed to capture different characteristics of water scarcity. Population, water availability, and water use are the key elements of these indicators. Most of the progress made in the last few decades has been on the quantification of water availability and use by applying spatially explicit models. However, challenges remain on appropriate incorporation of green water (soil moisture), water quality, environmental flow requirements, globalization, and virtual water trade in water scarcity assessment. Meanwhile, inter‐ and intra‐annual variability of water availability and use also calls for assessing the temporal dimension of water scarcity. It requires concerted efforts of hydrologists, economists, social scientists, and environmental scientists to develop integrated approaches to capture the multi‐faceted nature of water scarcity.
Key Points
We provide a comprehensive review of water scarcity indicators and reflect on their relevance in a rapidly changing world
There is a need to incorporate green water, water quality, and environmental flow requirements in water scarcity assessment
Integrated approaches are required to capture the multi‐faceted nature of water scarcity
The life cycle water scarcity footprint is a tool to evaluate anthropogenic contributions to regional water scarcity along global supply chains. Here, we complement it by a classification of the risk ...from human water use, a comprehensive conceptualisation of water use and a spatially-explicit impact assessment to a midpoint approach that assesses the risk of on-site and remote freshwater scarcity. For a 2 MWh Lithium-ion battery storage, the quantitative Water Scarcity Footprint, comprising physically used water, accounts for 33,155 regionally weighted m
3
with highest contributions from Chilean lithium mining. The qualitative Water Scarcity Footprint, the virtual volume required to dilute pollutant emissions to safe concentrations, is approximately determined to 52 million m
3
of regionally weighted demineralised water with highest contributions from copper and aluminium mining operations. As mining operations seem to have the highest impact, we recommend to consider the spatially-explicit water scarcity footprint for assessment of global material supply.
Hotspots of critical water usage along the global supply chain for a lithium-ion battery storage are mainly associated with mining activities, for example of lithium, aluminium and copper, according to a spatially explicit life cycle impact assessment.
Fresh water—the bloodstream of the biosphere—is at the center of the planetary drama of the Anthropocene. Water fluxes and stores regulate the Earth's climate and are essential for thriving aquatic ...and terrestrial ecosystems, as well as water, food, and energy security. But the water cycle is also being modified by humans at an unprecedented scale and rate. A holistic understanding of freshwater's role for Earth system resilience and the detection and monitoring of anthropogenic water cycle modifications across scales is urgent, yet existing methods and frameworks are not well suited for this. In this paper we highlight four core Earth system functions of water (hydroclimatic regulation, hydroecological regulation, storage, and transport) and key related processes. Building on systems and resilience theory, we review the evidence of regional‐scale regime shifts and disruptions of the Earth system functions of water. We then propose a framework for detecting, monitoring, and establishing safe limits to water cycle modifications and identify four possible spatially explicit methods for their quantification. In sum, this paper presents an ambitious scientific and policy grand challenge that could substantially improve our understanding of the role of water in the Earth system and cross‐scale management of water cycle modifications that would be a complementary approach to existing water management tools.
Plain language summary
Freshwater is crucially important for all life on Earth. There is abundant research and evidence on how different processes within the water cycle regulate climate and support ecosystems, and by extension, human societies. Humans are also a major force disturbing those processes and modifying the water cycle. These modifications include, for instance, surface water withdrawals, groundwater pumping, deforestation and other land cover change, and ice melt due to warming climate. As most previous research on human–water interactions focuses on understanding systems at smaller scales, such as a watershed or a nation, comprehensive understanding of what human modifications of the water cycle mean for the stability of the planet is still lacking. In this paper we propose a new framework for analysing and establishing limits to a variety of human modifications of the water cycle, to ensure that the stability of the Earth would not be compromised. We see this as an important and urgent scientific challenge that has the potential to substantially improve our understanding of the functioning of the Earth system and to inform local and global policy toward a more sustainable future.
Key Points
Earth system resilience depends on an improved understanding and management of water cycle modifications
We identify four key functions of freshwater in the Earth system and evidence of regional to global regime shifts and disruptions
The water planetary boundary is a compelling framework to improve our understanding and management of water cycle modifications in the Earth system
A global water model is used to analyse the impacts of climate change and socio-economic driving forces (derived from the A2 and B2 scenarios of IPCC) on future global water stress. This work extends ...previous global water research by analysing not only the impact of climate change and population, but also the effects of income, electricity production, water-use efficiency and other driving forces, on water stress. Depending on the scenario and climate model, water stress increases (between current conditions and the 2050s) over 62.0-75.8% of total river basin area and decreases over 19.7-29.0% of this area. The remaining areas have small changes. The principal cause of decreasing water stress (where it occurs) is the greater availability of water due to increased annual precipitation related to climate change. The principal cause of increasing water stress is growing water withdrawals, and the most important factor for this increase is the growth of domestic water use stimulated by income growth. (Population growth was a much less important factor and irrigated area was assumed to remain constant.) To address the uncertainty of water stress estimates, three different indicators of water stress were computed and compared. The overlap area of their computation of "severe stress" in the 2050s was large (approximately 23 × 10
6
km
2
or 56-73 % of the total "severe stress" area). This indicates a moderate level of agreement and robustness in estimates of future water stress. At the same time the indicators disagreed in many other areas, suggesting that work is still needed to elaborate general indicators and concepts of water stress.
As climate change brings about hotter and often drier summers, an improved understanding of how irrigation requirements vary according to climatic conditions is of increasing importance. Within ...Germany, temperate conditions have historically enabled most agriculture to be supplied solely by green water, but recent crop yield reductions and crop failures have demonstrated its increased vulnerability to climatic conditions. The raster-based mGROWA hydrological water balance model was implemented over all agricultural areas in Germany for the period 1961–2020 at a high spatial (200 m) and temporal (daily) resolution. Grid-cells were each assigned one of 10 major crop classes, which account for 86.7 % of all agricultural areas in Germany, and effectively all irrigated areas. Using crop-specific irrigation rules that reflect actual practices, irrigation requirements were simulated for all crop areas. To investigate the relationship between climatic water balance over the crop growing season and irrigation requirements, the simulated annual irrigation requirements were compared with the standardised precipitation-evapotranspiration index (SPEI-6), calculated at the end of September. Through this comparison, irrigation requirements could be characterised for near-normal and dry conditions, and results were aggregated to the district level. Additionally, using district-level data on the areas with irrigation infrastructure, the actual water used for irrigation was estimated. The results highlight marked increases in irrigation requirements in dry conditions compared to near-normal conditions (median increase of 72 %), which are more pronounced over crops in silty soils than in sandy soils. The results also demonstrate how the increased irrigation requirements in dry years are in many cases higher than what is suggested by guidelines for irrigation management in Germany. This study provides important information for actors related to the agricultural sector and water management and is based on a robust and transferable framework to quantify how irrigation requirements vary according to climatic variability and local soil conditions.
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•Irrigation requirements were simulated using mGROWA for agricultural areas in Germany.•Sharp increases in irrigation requirements were shown to occur in drought periods.•In dry years, irrigation requirements were highly pronounced for crops in silty soils.•Irrigation volumes were estimated by considering irrigation infrastructure data.
Extending assessments of climate change‐induced range shifts via correlative species distribution models by including species traits is crucial for conservation planning. However, comprehensive ...assessments of future distribution scenarios incorporating responses of biotic factors are poorly investigated. Therefore, the aim of our study was to extend the understanding about the combined usage of species traits data and species distribution models for different life stages and distribution scenarios. We combine global model predictions for the 2050s and thermal performances of Salmo trutta and Salmo salar under consideration of different life stages (adults, juveniles, eggs), timeframes (monthly, seasonally, yearly), and dispersal scenarios (no dispersal, free dispersal, restricted dispersal). We demonstrate that thermal performances of different life stages will either increase or decrease for certain time periods. Model predictions and thermal performances imply range declines and poleward shifts. Dispersal to suitable habitats will be an important factor mitigating warming effects; however, dams may block paths to areas linked to high performances. Our results emphasize enhanced inclusion of critical periods for species and proper dispersal solutions in conservation planning.
For Salmo trutta and Salmo salar, we combine species distribution models with thermal performance curves for different life stages, time frames, and dispersal scenarios to assess future impacts of climate change. We show varying thermal performances for different life stages and time periods, range declines, and adverse impacts of dispersal barriers. Our results emphasize enhanced inclusion of critical time periods and consideration of dispersal possibilities.
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