African Water Development Report 2006 - United Nations Economic ...

annual flows of rivers and groundwater that aregenerated from the rainfall that occurs within thesubregion (UNECA, 2001). The final four columnsprovide information on the total amountof water withdrawn in each of the subregions foragriculture (85 per cent), community water supply(9 per cent), and industry (6 per cent).It must be noted that rainfall anomalies, bothpositive and negative, are very frequent over thecontinent. Most freshwater comes from seasonalrains, which vary with the climatic zone. Theheaviest rainfall occurs along the equator, especiallythe area from the Niger Delta to the CongoRiver Basin. The Sahara Desert has virtuallyno rain. Northern and Southern Africa receive 9and 12 per cent, respectively, of the region’s rainfall(FAO 1995). In West and Central Africa,rainfall is exceptionally variable and unpredictable(UNECA, 2001).Internal renewable resourcesprecipitation (fig. 4.2). Major runoff characteristicsof principal river basin systems in Africa areshown in table 4.3 with the Congo river being thelargest and having the highest runoff volume of1300 km 3 /year Generally the amounts of surfaceand groundwater flows that are generated fromrainfall within the subregions are all low (table4.4). At the continental level, the renewable waterresources constitute only about 20 per cent of thetotal rainfall. In the Sudano-Sahelian and SouthernAfrican regions, the figures are 5.9 and 9.25per cent, respectively. This may reflect high lossesfrom the rainfall. These losses may occur, in part,through evaporation from surface waters or fromplants. The low values of the internal renewableresources also show that there is room for improvementin conservation of rainwater, the lack ofwhich accounts, in part, for the endemic droughtin parts of the continent (UNECA, 2001). Theactual renewable water resources are shown at thecontinental level in figure 4.3 and relative countryvalues are also demonstrated by subregion in figure4.4 and table 4.5.FRESHWATER RESOURCES IN AFRICAA second significant feature of water resources inAfrica is the extremely low runoff in relation toFigure 4.2: Mean Annual Runoff - AfricaAn example of abundant renewable water isfound in the Democratic Republic of the Congo,Source: UNEP-Vital Climate Graphics Africa, 200255