A grid-based approach to water scarcity estimates for eastern and southern Africa

A novel approach is taken to the problem of estimating global water scarcity, using a realistic and consistent procedure applied across many countries. Water demands, surface flows and groundwater availability are estimated on a gridded basis, and various water availability indices are derived comparing the resource with the projected demand. Surface flows are estimated using a conceptual rainfall-runoff model linking climate to runoff and, in the major river basins, the runoff estimates for individual grid cells are accumulated to give estimates for the total flows at all points of interest. Groundwater availability is derived from hydrogeological maps based on estimates of the potential yield that can be expected from a borehole and the likely maximum borehole density. Estimates of potential groundwater recharge derived from the surface water model are also taken into account. Water demands are based on current and projected population and livestock numbers, and information on irrigation schemes and industrial water use. Results are presented for the application of the model to a region covering the whole of eastern and southern Africa. The main scenario considered includes the combined impact of climate change, population growth and improved living standards to the year 2050. The results for this scenario show that water scarcity is likely to increase in many countries in the region, with particular problems in the countries around Lake Victoria and in the southernmost parts of the pilot region.