EVAPORATION IN EAST AFRICA

Abstract

Following a decision to estimate potential evaporation from meteorological observations rather than from evaporation pans, 53 agricultural meteorological stations were established over East Africa with the co-operation of several departments of three governments. Supplementary information from an additional 123 less well equipped stations was incorporated into the preparation of maps of monthly potential open water evaporation, using the Penman estimate. Annual values of potential evaporation range from more than 2,600 mm to less than 1,400 mm with 70% of the area of East Africa having potential evaporation rates, of between 1,800 and 2,200 mm per annum. There are marked seasonal variations in evaporation rates, mainly dependent on patterns of cloud cover, but average monthly rates rarely fall below 90 mm even in highland areas. These high rates of water demand have serious implications for the management of water catchments, land planning, crop breeding, tillage techniques, ground water recharge and rates of primary productivity in rangeland.