| | Drylands: Major Watersheds |
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| Analytical Overview |
| The major watershed basin GIS coverage used in this map is from Revenga, et al, 1998. An analysis was conducted to determine the amount of dryland area in each basin. Watershed basins containing more than 50% dryland area are included in whole and are labeled on this map. |
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Map Projection
Geographic
Map Description
This map shows major watersheds of the world with at least 50 percent of their area within the dryland aridity zones. Summary statistics of these basins show that their areas range from approximately 52 thousand km2 to nearly 3 million km2. A summary of some of the indicators for these dryland basins include the following:
These basins include a wide range of population densities, from an average of 1 person per km2 in the Chubut basin to an average of 398 people per km2 in the Ganges basin (For more information on the Chubut and Ganges basins, see the maps under the heading "Water Resources and Freshwater Ecosystems" titled WATERSHEDS OF THE WORLD: SOUTH AMERICA - CHUBUT WATERSHED and WATERSHEDS OF THE WORLD: ASIA AND OCEANIA - GANGES WATERSHED) ;
The major dryland basins of Asia and Europe tend to have larger percentages of their area in cropland and built-up area than other regions of the world;
These major dryland basins of Asia and Europe also tend to have larger percentages of irrigated area, up to as much as 24 percent (Indus and Narmada), contrasting with the dryland basins in the remaining regions, such as the Senegal basin, which does not have any irrigated land (For more information on the Senegal basin, see map under heading "Water Resources and Freshwater Ecosystems" titled WATERSHEDS OF THE WORLD: AFRICA - SENEGAL WATERSHED);
The percentage of wetland in all of these major dryland basins is generally low, but over half contain at least one Ramsar site and some contain over five Ramsar sites. (Ramsar sites are wetlands which have been designated for inclusion on the List of Wetlands of International Importance.);
The basins tend to have very few or no large dams under construction, with one major exception: Tigris & Euphrates, with 19 large dams in progress (For more information on the Tigris & Euphrates basin, see map under heading "Water Resources and Freshwater Ecosystems" titled WATERSHEDS OF THE WORLD: EUROPE - TIGRIS & EUPHRATES WATERSHED );
Although generally without large dams in progress, many basins (where data are available) exhibit a high degree of modification (i.e. existing dams, reservoirs, interbasin transfers, and irrigation consumption), including many basins in Asia such as the Huang He (For more information on the Huang He basin, see map under heading "Water Resources and Freshwater Ecosystems" titled WATERSHEDS OF THE WORLD: ASIA AND OCEANIA - HWANG HE WATERSHED).
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Citation:
WRI. 2002. World Resources Institute. Drylands, People, and Ecosystem Goods and Services: A Web-based Geospatial Analysis. Available online at: http://www.wri.org
Sources:- Revenga, C., S. Murray, J. Abramowitz, and A. Hammond. 1998, Watersheds of the World: Ecological Value and Vulnerability.Washington, DC:World Resources Institute and Worldwatch Institute.
- United Nations Environment Program/Global Resource Information Database. Prepared by U. Diechmann and L. Eklundh. 1991, Global Digital Datasets for
Land Degradation Studies: a GIS Approach. Nairobi, Kenya:UNEP/GEMS and GRID.
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