Indicator Code: WATSTR
Objective: Ecosystem Vitality
Policy Category: Water
Subcategory: Water (Effects on Environment)
Indicator Short Name: Water Stress
Indicator Full Name: Percentage of National Territory Experiencing Water Stress (withdrawals exceed 40% of available supply)
Indicator Description: The EPI water stress indicator is the percentage of a country’s territory affected by oversubscription of water resources. A high degree of oversubscription is indicated when the water use is more than 40% of available supply (WMO, 1997). Countries can to some extent accommodate oversubscription in one region with inter-basin transfers, water re-use and desalination but some of these engender significant environmental impacts of their own. Thus, the ultimate target for each country is to have no area of their territory affected by oversubscription.
Units: Percentage of national territory with water withdrawals exceeds 40% of available supply
Country Coverage: 171
Reference Year: Contemporary (mean annual 1950-1995)
Target: 0 percent
Target Source: Expert Judgment
Short Source: University of New Hampshire, Water Systems Analysis Group.
Source: University of New Hampshire, Water Systems Analysis Group.
Source URL: http://www.watsys.sr.unh.edu
Methodology: Human water demand was computed using the following data sources: population per grid cell; per capita country or sub national level industrial water demand; irrigated land extent per grid cell according to Döll et al. (2000); and country or sub national level agricultural water demand (irrigation). Global discharge fields were computed by blending mean annual discharge observations (where available) with a climatology (1950-1995) of discharge output from the Water Balance Model based on Vörösmarty et al. (1998).
An indicator of relative water demand (RWD) for each 1/4 degree grid cell was computed by dividing total human water demand (domestic + industrial + agricultural water or DIA) by renewable water supply (Q). RWD = 0.4 was established as the threshold for water stressed conditions. The percentage of territory in which water resources are oversubscribed was computed by summing the area of grid cells in each country where RWD >= 0.4. Details on the computation and use of RWD (alternatively known as the Relative Water Stress Index or RWSI) can be found in Vörösmarty et al. (2000) and Vörösmarty et al. (2005).
Additional Citations: Döll, P., Siebert, S. 2000. A digital global map of irrigated areas. ICID Journal, 49(2), 55-66.
Vörösmarty, C. J., C. A. Federer and A. L. Schloss. (1998). Evaporation functions compared on US watershed: Possible implications for global-scale water balance and terrestrial ecosystem modeling, Journal of Hydrology, 207 (3-4): 147-169.
WMO (World Meteorological Organization).et al. (1997). Comprehensive Assessment of the Freshwater Resources of the World. Geneva, Switzerland.
Vörösmarty, C. J., P. Green, J. Salisbury and R. B. Lammers. (2000). Global water resources: vulnerability from climate change and population growth, Science, 289:284-288.
Vörösmarty, C. J., E. M. Douglas, P. Green and C. Revenga. (2005). Geospatial Indicators of Emerging Water Stress: An Application to Africa, Ambio, 34 (3): 230-236.