Drylands: Projected Water Supply in Major Watersheds in Drylands, 2025
| Analytical Overview |
| The projected water supply data for the year 2025 used in this map was developed by combining a global population database for 1995 that uses census data for over 120,000 administrative units (CIESIN et al. 2000) and a global runoff database developed by the University of New Hampshire and the WMO/Global Runoff Data Centre (Fekete et al. 1999). The runoff database combines observed discharge data from monitoring stations with a water balance model driven by climate variables such as temperature, precipitation, land cover, and soil information. For those regions where discharged data were available, the modeled runoff was adjusted to match the observed values; for regions with no observed data the modeled estimates of runoff were used (Fekete et al. 1999). The 2025 estimates are considered conservative because they are based on the United Nations’ low-range projections for population growth, which has population peaking at 7.2 billion in 2025 (UNPD 1999:3). In addition, a slight mismatch between the water runoff and population data sets leaves 4 percent of the global population unaccounted for in this analysis. This data was then linked to the GIS watershed basin coverage from Revenga, et al., 1998 (see map, Drylands: Major Watersheds). Results of annual renewable water supply for the year 2025 are displayed in cubic meters per person per year. |
Map Projection
Geographic
Map Description
Two indicators used to evaluate the status of freshwater resources include water stress and water scarcity. Water stress has been defined as when a country’s annual water supplies are below 1,700 cubic meters per person and is characterized by periodic water shortages. Water scarcity is when annual water supplies are below 1,000 cubic meters per person, producing chronic shortages of freshwater and subsequent negative effects on food production, economic development, and ecosystem health.
This map shows the projected water supply in major watersheds in drylands for the year 2025. Many basins appear to have sufficient water for their populations in 2025. In other basins, however, the mapped data suggest that problems with water supply will occur in the near future.
Seven basins in drylands are projected to be water stressed in 2025. These basins, found mostly in Asia, with one in Africa and one in North America, may experience periods of water shortages, with less than 1,700 cubic meters of water available per person per year. Fourteen of the major watersheds in drylands are projected to be water scarce in 2025. These 14 basins in Asia, Africa, as well as North America may experience chronic shortages of freshwater with less than 1000 cubic meters of water available per person per year. In total, half of the major watersheds examined in drylands are predicted to experience some type of water shortage in the coming years.
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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.
- Fekete, B., C.J. Vörösmarty, and W. Grabs. 1999, Global, Composite Runoff Fields Based on Observed River Discharge and Simulated Water Balance. Koblenz, Germany: WMO-GRDC.