Friday, March 3, 2006
The Science of Global Warming: Surface Water Availability Declines More Rapidly Than Mean Rainfall So Surface Water Supplies Will Drop Across 25% of Africa By the End of the Century
DeWit and Stankiewicz report in Science that surface water drainage (supply) has a non-linear relationship to rainfall in Africa. A 10% drop in rainfall in an area with 40 inches (1000mm) of rain will reduce surface water drainage by 17%. The same 10% drop in rainfall in an area with 20 inches (500mm) of rain will reduce surface water drainage by 50%. So the rainfall reductions associated with climate change will affect areas with intermediate rainfall most dramatically. Deserts may become uninhabitable, but areas of moderate rainfall will lose enormous quantities of their surface water supplies. DeWit and Stankiewicz estimate that surface water access will be reduce across 25% of Africa by the end of this century.
Abstract: Across Africa, perennial drainage density as a function of mean annual rainfall defines three regimes separated by threshold values of precipitation. This non-linear response of drainage to rainfall will most seriously affect regions in the intermediate, unstable, regime. A 10% decrease in precipitation in regions on the upper regime boundary (1000 mm/y) would reduce drainage by 17%, while in regions receiving 500 mm/y such a drop would cut 50% of surface drainage. Using predicted precipitation changes, we calculate that decrease in perennial drainage will significantly affect present surface water access across 25% of Africa by the end of this century.