Global Water Assessments Research Articles

At the nexus of fire, water and society

The societal risks of water scarcity and water-quality impairment have received considerable attention, evidenced by recent analyses of these topics by the 2030 Water Resources Group, the United Nations and the World Economic Forum. What are the effects of fire on the predicted water scarcity and declines in water quality? Drinking water supplies for humans, the emphasis of this exploration, are derived from several land cover types, including forests, grasslands and peatlands, which are vulnerable to fire. In the last two decades, fires have affected the water supply catchments of Denver (CO) and other southwestern US cities, and four major Australian cities including Sydney, Canberra, Adelaide and Melbourne. In the same time period, several, though not all, national, regional and global water assessments have included fire in evaluations of the risks that affect water supplies. The objective of this discussion is to explore the nexus of fire, water and society with the hope that a more explicit understanding of fire effects on water supplies will encourage the incorporation of fire into future assessments of water supplies, into the pyrogeography conceptual framework and into planning efforts directed at water resiliency.This article is part of the themed issue 'The interaction of fire and mankind'.

Accounting for environmental flow requirements in global water assessments

Abstract. As the water requirement for food production and other human needs grows, quantification of environmental flow requirements (EFRs) is necessary to assess the amount of water needed to sustain freshwater ecosystems. EFRs are the result of the quantification of water necessary to sustain the riverine ecosystem, which is calculated from the mean of an environmental flow (EF) method. In this study, five EF methods for calculating EFRs were compared with 11 case studies of locally assessed EFRs. We used three existing methods (Smakhtin, Tennant, and Tessmann) and two newly developed methods (the variable monthly flow method (VMF) and the Q90_Q50 method). All methods were compared globally and validated at local scales while mimicking the natural flow regime. The VMF and the Tessmann methods use algorithms to classify the flow regime into high, intermediate, and low-flow months and they take into account intra-annual variability by allocating EFRs with a percentage of mean monthly flow (MMF). The Q90_Q50 method allocates annual flow quantiles (Q90 and Q50) depending on the flow season. The results showed that, on average, 37% of annual discharge was required to sustain environmental flow requirement. More water is needed for environmental flows during low-flow periods (46–71% of average low-flows) compared to high-flow periods (17–45% of average high-flows). Environmental flow requirements estimates from the Tennant, Q90_Q50, and Smakhtin methods were higher than the locally calculated EFRs for river systems with relatively stable flows and were lower than the locally calculated EFRs for rivers with variable flows. The VMF and Tessmann methods showed the highest correlation with the locally calculated EFRs (R2=0.91). The main difference between the Tessmann and VMF methods is that the Tessmann method allocates all water to EFRs in low-flow periods while the VMF method allocates 60% of the flow in low-flow periods. Thus, other water sectors such as irrigation can withdraw up to 40% of the flow during the low-flow season and freshwater ecosystems can still be kept in reasonable ecological condition. The global applicability of the five methods was tested using the global vegetation and the Lund-Potsdam-Jena managed land (LPJmL) hydrological model. The calculated global annual EFRs for fair ecological conditions represent between 25 and 46% of mean annual flow (MAF). Variable flow regimes, such as the Nile, have lower EFRs (ranging from 12 to 48% of MAF) than stable tropical regimes such as the Amazon (which has EFRs ranging from 30 to 67% of MAF).

The future for global water assessment

The global water cycle is a fundamental component of our climate and Earth system. Many, if not the majority, of the impacts of climate change are water related. We have an imperfect description and understanding of components of the water cycle. This arises from an incomplete observation of some of the stores and fluxes in the water cycle (in particular: precipitation, evaporation, soil moisture and groundwater), problems with the simulation of precipitation by global climate models and the wide diversity of global hydrological models currently in use. This paper discusses these sources of errors and, in particular, explores the errors and advantages of bias correcting climate model outputs for hydrological models using a single large catchment as an example (the Rhine). One conclusion from this analysis is that bias correction is necessary and has an impact on the mean flows and their seasonal cycle. However choice of hydrological model has an equal, if not larger effect on the quality of the simulation. The paper highlights the importance of improving hydrological models, which run at a continental and global scale, and the importance of quantifying uncertainties in impact studies.

Water quality assessment at a global scale: a comparison between world regions

This paper examines the state of global drinking water quality using the Global Drinking Water Quality Index (GDWQI) for freshwater ecosystems. We compared the state of water quality in the five major world regions over 30 years by using a database provided by the GEMS/Water Programme of the United Nations Environment Program Global Environment Monitoring System. This global monitoring database is unique in the world and consists of raw, real data, not modelled data as is typical for many global water assessments. Our findings confirm the applicability of the GDWQI to better communicate changes in water quality trends and therefore help to improve decision-making processes worldwide.

Water Demands for Bioenergy Production

The pressure to shift increasingly to renewable energy sources is escalating. The Johannesburg World Summit of Sustainable Development of 2002 defined in its Plan of Implementation that the global share of renewable energy sources should be increased substantially. Today, renewables account for 13.1% of the world's primary energy production. Eighty per cent of all renewable energy comes from biomass and 16% from hydropower. These two sources will thus be set under particular growth pressure in future years. This paper assesses the water needs of current and future bioenergy production and concludes that it is one of the major water consumers of this planet, although much neglected in global water assessments. The pressure to increase the share of bioenergy in the global account puts a considerable strain on water resources in all continents, but the challenges will be most pronounced in Asia and Africa.

EHPnet: UNEP.Net Freshwater Portal

Vol. 113, No. 7 EnvironewsOpen AccessEHPnet: UNEP.Net Freshwater Portal Erin E. Dooley Erin E. Dooley Search for more papers by this author Published:1 July 2005https://doi.org/10.1289/ehp.113-a451AboutSectionsPDF ToolsDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InReddit Even though 70% of the Earth’s surface is covered with water, little of that is freshwater. Today, one-third of the world’s population lives in countries with moderate or high water stress, a fact that leads many experts to proclaim that water may possibly be the primary cause of international tensions and the foremost threat to environmental health in the twenty-first century. The United Nations Environment Programme (UNEP) has set up a Freshwater Portal, located online at http://freshwater.unep.net/, as a centralized resource for anyone looking to learn more about freshwater use, resources, and scarcity. The fully searchable site is part of UNEP’s United Nations Environment Network, which aims to bring specialized environmental science communities together under one umbrella.The issues associated with freshwater resources are wide-ranging. Many surface water sources are shrinking, as population growth fuels desertification and overuse of resources. Several large rivers now run dry for at least part of the year, and lakes are shrinking. Groundwater, too, is being affected by pollution, salinization, and overuse. Overpumping of water is causing large areas to sink, including almost 60,000 square miles in China. Infrastructure also is in crisis in many areas. In 2002, only 52% of people worldwide were connected to water systems, and only 30% were connected to sanitation services. Each year more than 5 million people die from water-related diseases, and diarrheal diseases are the leading cause of death in children.The Freshwater Portal has been indexed by nine key issues. These include water scarcity, irrigated agriculture, water and sanitation, water quality, groundwater, transboundary water management, water and ecosystems, floods and droughts, and urban water. For each key issue, UNEP has collected relevant reports, background papers, websites, and other resources. For example, the Water Scarcity section includes links to papers on balancing water uses, managing water within agriculture, and the relationship between water scarcity and poverty. The Water and Sanitation section provides links to two reports as well as to the World Bank Water and Sanitation Program, which guides international efforts to build infrastructure in this area. And the Groundwater section links to a global overview of ground-water conditions, which goes on to detail best management practices for this resource.The site is also cross-indexed by resource type. Visitors can view all case studies/best practices documents, for example, or go directly to conference proceedings covering multiple topic areas.Similar portals on other topics are accessible from the top of the homepage. Visitors can choose other Thematic Portals, such as Climate Change or Urban Environment, and can also select from Regional Portals to view information specific to the Arctic, Europe, or Latin America. The homepage also highlights global water assessments and announcements of recent documents, statements, and meetings. Also included is a link to Earthprint.com, where visitors can purchase freshwater publications produced by UNEP and other international organizations.FiguresReferencesRelatedDetails Vol. 113, No. 7 July 2005Metrics About Article Metrics Publication History Originally published1 July 2005Published in print1 July 2005 Financial disclosuresPDF download License information EHP is an open-access journal published with support from the National Institute of Environmental Health Sciences, National Institutes of Health. All content is public domain unless otherwise noted. Note to readers with disabilities EHP strives to ensure that all journal content is accessible to all readers. However, some figures and Supplemental Material published in EHP articles may not conform to 508 standards due to the complexity of the information being presented. If you need assistance accessing journal content, please contact [email protected]. Our staff will work with you to assess and meet your accessibility needs within 3 working days.

Geospatial Indicators of Emerging Water Stress: An Application to Africa

This study demonstrates the use of globally available Earth system science data sets for water assessment in otherwise information-poor regions of the world. Geospatial analysis at 8 km resolution shows that 64% of Africans rely on water resources that are limited and highly variable. Where available, river corridor flow is critical in augmenting local runoff, reducing impacts of climate variability, and improving access to freshwater. A significant fraction of cropland resides in Africa's driest regions, with 39% of the irrigation nonsustainable. Chronic overuse and water stress is high for 25% of the population with an additional 13% experiencing drought-related stress once each generation. Paradoxically, water stress for the vast majority of Africans typically remains low, reflecting poor water infrastructure and service, and low levels of use. Modest increases in water use could reduce constraints on economic development, pollution, and challenges to human health. Developing explicit geospatial indicators that link biogeophysical, socioeconomic, and engineering perspectives constitutes an important next step in global water assessment.

A Pilot Global Assessment of Environmental Water Requirements and Scarcity

This paper presents a first attempt to estimate the volume of water required for the maintenance of freshwater-dependent ecosystems at the global scale. This total environmental water requirement consists of ecologically relevant low-flow and high-flow components and depends upon the objective of environmental water management. Both components are related to river flow variability and estimated by conceptual rules from discharge time series simulated by the global hydrology model. A water stress indicator is further defined, which shows what proportion of the utilizable water in world river basins is currently withdrawn for direct human use and where this use is in conflict with environmental water requirements. The paper presents an estimate of environmental water requirements for 128 major river basins and drainage regions of the world. It is shown that approximately 20 to 50 percent of the mean annual river flow in different basins needs to be allocated to freshwater-dependent ecosystems to maintain them in fair conditions. This is unlikely to be possible in many developing countries in Asia and North Africa, in parts of Australia, North America, and Europe, where current total direct water withdrawals (primarily for irrigation) already tap into the estimated environmental water requirements. Over 1.4 billion people currently live in river basins with high environmental water stress. This number will increase as water withdrawals grow and if environmental water allocations remain beyond the common practice in river basin management. This paper suggests that estimates of environmental water requirements should be the integral part of global water assessments and projections of global food production.

Development and testing of the WaterGAP 2 global model of water use and availability

Growing interest in global environmental issues has led to the need for global and regional assessment of water resources. A global water assessment model called “WaterGAP 2” is described, which consists of two main components'a Global Water Use model and a Global Hydrology model. These components are used to compute water use and availability on the river basin level. The Global Water Use model consists of (a) domestic and industry sectors which take into account the effect of structural and technological changes on water use, and (b) an agriculture sector which accounts especially for the effect of climate on irrigation water requirements. The Global Hydrology model calculates surface runoff and groundwater recharge based on the computation of daily water balances of the soil and canopy. A water balance is also performed for surface waters, and river flow is routed via a global flow routing scheme. The Global Hydrology model provides a testable method for taking into account the effects of climate and land cover on runoff. The components of the model have been calibrated and tested against data on water use and runoff from river basins throughout the world. Although its performance can and needs to be improved, the WaterGAP 2 model already provides a consistent method to fill in many of the existing gaps in water resources data in many parts of the world. It also provides a coherent approach for generating scenarios of changes in water resources. Hence, it is especially useful as a tool for globally comparing the water situation in river basins.

Global water assessment and potential contributions from Earth Systems Science

Earth Systems Science has made significant strides over the last decade in developing consistent, high quality, spatially-contiguous, and in many cases real-time bioegoephysical data sets. Many of these data sources depict key elements of the land-based water cycle. To date, this information has been poorly integrated into global water assessment and vulnerability studies. This paper presents a review of newly-emerging Earth Systems Science products together with a strategy for entraining these into global water assessments. The text highlights several conceptual, technical, and institutional obstacles that require attention before a successful integration can be realized. A major challenge rests in developing a common conceptual framework and nomenclature to bridge gaps between the physical sciences and current generation of water resource assessments, which have traditionally relied heavily on descriptive case studies and a socioeconomic approach. Another goal of this paper is to better articulate the scope of human control of the terrestrial water cycle – beyond climate change alone – and to quantify its impact on sustainable water supplies. Opportunities for integration across disciplines are identified, and specific recommendations are formulated. An argument is made for the unique role that geographically-referenced continental and global-scale analysis can play in future assessments of freshwater resources and water-related vulnerability.