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Reliable Monthly Water Discharge Print E-mail
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Discharge in each grid cell (surface runoff plus groundwater recharge) resulting from the accumulation of runoff as rivers run downstream. This is a statistical estimate of the minimum monthly flow which occurs over 90% of the months during the climate normal period (1961-90).

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

DescriptionReliable Monthly Water Discharge

Standing out in the map of reliable discharge are the great river carriers of the world such as the Amazon in Latin America, the Yangtze in China, and the Congo in Central Africa which drain large areas and dependably provide large volumes of water in all but the driest of years.


Climate varies from season-to-season and year-to-year, and this causes large temporal swings in runoff and discharge. In most drainage basins the difference between the highest and lowest monthly discharge is indeed quite large; in temperate regions river discharge is often enormous because of snowmelt in late winter or early spring and very low in late summer or early autumn because of higher evaporation and lower precipitation. Many tropical regions experience enormous peaks in river discharge during the annual monsoon rains and have minimal flow at the end of the dry season. Besides the relatively predictable seasonal variation in climate, there is also the more unpredictable variation between years which lead to periodic "drier than normal" years and low river flows. Because of these variations, the long-term averages (long-term average runoff and long-term average water resources) are not particularly good indicators of the water resources that can be counted on each year. A better measure is the "90% reliable monthly discharge" which is the minimum discharge expected in all but the driest 10% of the driest months.


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


The dataset 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 10: Reliable Monthly Water Discharge (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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