Water resources are inextricably linked with climate, so the prospect of global climate change has serious implications for water resources and regional development (Riebsame et al., 1995). Efforts to provide adequate water resources for Africa will confront several challenges, including population pressure; problems associated with land use, such as erosion/siltation; and possible ecological consequences of land-use change on the hydrological cycle. Climate change-especially changes in climate variability through droughts and flooding-will make addressing these problems more complex. The greatest impact will continue to be felt by the poor, who have the most limited access to water resources.
Availability of water in sub-Saharan Africa (SSA) is highly variable. Only the humid tropical zones in central and West Africa have abundant water. According to Sharma et al. (1996), eight countries were suffering from water stress or scarcity in 1990; this situation is getting worse as a consequence of rapid population growth, expanding urbanization, and increased economic development. By 2000, about 300 million Africans risk living in a water-scarce environment. More over, by 2025, the number of countries experiencing water stress will rise to 18 affecting 600 million people (World Bank, 1995).
Many countries will shift from water surplus to water scarcity as a result of population changes alone between 1990 and 2025, using a per capita water-scarcity limit of 1,000 m3 yr-1. Long-term precipitation records from the Sahara give a clear indication of declining precipitation in that region (UNEP, 1997). These declines in precipitation register as reduced h y d rological discharges in major river basins in the sub humid zones. It is apparent that several countries will face water availability restrictions by the middle of the 21st century, if current consumption trends persist. The combination of demographic trends and climate change is likely to cause economically significant constraints in some parts of Africa.
(IPCC Climate Change 2001: Impacts, Adaptation and Vulnerability 10.2.1).