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

African Water Development Report 2006Most African countries also experience extremesof rainfall (periodic flooding or drought). Thereis some evidence that both droughts and floodshave increased in frequency and severity over thepast 30 years (OFDA 2000). The Sahelian zone,in particular, is now experiencing a continued declinein rainfall compared to pre-1960s averages,and Lake Chad has shrunk to 5 per cent of itssize 35 years ago (NASA Global Earth ObservingSystem 2001). Severe droughts were experiencedin 1973 and 1984 when almost all Africancountries suffered reduced rainfall which particularlyaffected several million people in the Hornof Africa, the Sahel and Southern Africa.In contrast, the northern and eastern parts of Africaare subject to occasional floods, the most significantrecent example being in 1999–2000 whenexcessive rains affected Mozambique, Botswana,Zambia, Zimbabwe and South Africa, floodingsome 200 000 ha of cropland and affecting morethan 150 000 families. The estimated cost of recoveryis millions of US dollars (Mpofu 2000).Although the SADC Early Warning System wasable to predict the heavy rains, most of the countriesaffected were ill-prepared for the magnitudeand duration of the floods. The result was investigationand revision of response strategies.Rainfall Patterns over AfricaMost of Africa has a warm or hot climate, but thehumidity and amount of rainfall vary dramaticallyfrom area to area. Rainfall is distributedvery unevenly in Africa. Most areas receive eithertoo much or too little rain. In parts of thewest coast, for example, annual rainfall averagesmore than 100 inches (250 centimetres). In Monrovia,Liberia, an average of more than 40 inches(100 centimetres) of rain falls during the monthof June alone. In contrast, more than half of Africareceives less than 20 inches (50 centimetres)of rainfall yearly; the Sahara and the NamibianDesert receive an average of less than 10 inches(25 centimetres). In parts of the deserts, rainmay not fall for six or seven years in a row. Rainfalls throughout the year in the forests of theCongo Basin and the coastal regions of westernAfrica. But almost all the rest of Africa has oneor two seasons of heavy rainfall separated by dryperiods. In some regions of Africa, the amountof rainfall varies sharply from year to year ratherthan from season to season. Inter-annual variationscan be extremely high, and drought and/orflooding is common in most African countries.The cost of such extreme events runs into millionsof dollars every year, a price that many Af-Figure 10.2: Rainfall fluctuatins in Africa 1900-2000Sources:: FAO; http//www.unep.org/dewa/Africa230