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Discharge as runoff accumulated within drainage basins (accounting for evaporation from lakes and wetlands) for the "climate normal" period (1961-90).

Map description and dataset provided by: Center for Environmental Systems Research (CESR), Kassel, Germany

DescriptionWater Resources

The Map depicts the average water resources available in drainage basins each year over the long-run. This map sharpens the contrast between adjacent water-rich and water-poor areas. For example, the differences in water availability between northern and southern India, and between northwestern and western North America become more clear.


Among its other characteristics, water is a transportable substance - and can be transported either naturally through river beds and gulleys, or artificially through culvert and piping systems. For this reason water can be distributed and made available to users at some distance from its source. But most of the runoff generated within a drainage basin is distributed and used within the same basin because the alternative - pumping water over the hills and mountains on its edges - is usually too technically difficult and/or expensive. Waters within a basin are often stored in reservoirs and distributed within a basin by gravity flow. Hence a part of a drainage basin with more runoff can compensate for another part of the basin with less runoff, and the total discharge over drainage basin area is an approximate measure of the water available to the population in the basin.


The dataset for this map was provided by: Joseph Alcamo, Center for Environmental Systems Research (CESR), Kassel, Germany


The data was developed for the World Water Assessment Report (to be included in Report Chapter IV. Current State of the World's Freshwater and Ecosystems, Section 1. The Nature of the Resource). The data is representing an output of the Water GAP model version 2.1D.


Please cite this map as: "GWSP Digital Water Atlas (2008). Map 2: Water Resources (V1.0). Available online at http://atlas.gwsp.org."

Contact Information

For further information please contact: Frank Voss or Martina Flörke, Center for Environmental Systems Research, Kurt-Wolter-Str.3, 34109 Kassel, This e-mail address is being protected from spam bots, you need JavaScript enabled to view it or This e-mail address is being protected from spam bots, you need JavaScript enabled to view it ; Phone: +49.561.804.3902, Fax: +49.561.804.3076

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