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Assessment of water availability, water use and water stress at the global scale has been the subject of increasingly intensive research over the course of the past 10 years.

TitleTaking into account environmental water requirements in global-scale water resources assessments
Publication TypeBook
Year of Publication2004
AuthorsRevenga, C, Smakhtin, V, Doll, P, Colombo, LKComprehens
Secondary TitleResearch report / IWMI
Volumeno. 2
Paginationv, 24 p. : 7 fig., 2 tab.
Date Published2004-01-01
PublisherComprehensive Assessment Secretariat
Place PublishedColombo, Sri Lanka
ISBN Number9290905425
Keywordsagriculture, comprehensive assessment of water management in agriculture, ecosystems, environmental impact, hydrology, natural resources, sdiwrm, water demand, water quantity, water resources management, water shortage, water use
Abstract

Assessment of water availability, water use and water stress at the global scale has been the subject of increasingly intensive research over the course of the past 10 years. However, the requirements of aquatic ecosystems for water have not been considered explicitly in such assessments. It is, however, critically important that in global studies a certain volume of water is planned for the maintenance of freshwater ecosystem functions and the services they provide to humans. This report summarizes the results of the first pilot global assessment of the total volumes of water required for such purposes in world river basins. These volumes are referred to in this report as Environmental Water Requirements (EWR). The total EWR are assumed to consist of ecologically relevant lowflow and high-flow components. Both components are related to river flow variability, and estimated by conceptual rules from the discharge time series simulated by the global hydrology model. The concept of environmental water scarcity is then introduced and analyzed using a water stress indicator, which shows what proportion of the utilisable water in world river basins is currently withdrawn for direct human use and where this use is in conflict with EWR. The results are presented on global maps. EWR required to maintain a fair condition of freshwater ecosystems range globally from 20 to 50 percent of the mean annual river flow in a basin. It is shown that even at estimated modest levels of EWR, parts of the world are already or soon will be classified as environmentally water scarce or environmentally water stressed. The total population living in basins where modest EWR levels are already in conflict with current water use, is over 1.4 billion, and this number is growing. The necessity of further research in this field is advocated and the directions for such research are discussed. [author abstract]

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