A GEOSPATIAL APPROACH TO WATER STRESS IN AFRICA

We analyze a set of geographically-specific indicators of African water scarcity. These indicators at 6' (longitude x latitude) spatial resolution show that a significant fraction of the African population (40%) and its associated water demands are located in water-scarce regions with <100 mm yr-1 runoff. The same fraction of African agricultural land is exposed to a climate where potential evapotranspiration exceeds annual rainfall. These areas show a large degree of intra- and interannual variability in available water supply. Consequently, agricultural demand defines the aggregate water use for the continent. Paradoxically, the mean annual relative water use stress index for most of the African population is low. To some degree, chronic seasonal shortages of water may be more critical; 200 million people (30%) are exposed to water stress for more than 10 months per year. We demonstrate that river corridor discharge is critical in augmenting local runoff in arid regions, reducing the impact of climate variability, and improving access to water supply. We present a water stress severity index, based on hydrologic and socioeconomic indicators, for assessing future water scarcity conditions.