The drying up of east African rift valley lakes in recent times with special reference to lake Elmenteita.

Abstract

Possible causes of the drying up of Lake Elmenteita and its feeder rivers during 1958-1987 were studied. The effects of the changing climate elements of rainfall and evapotranspiration as well as the possible contributions of land cover and land use changes were considered. Results indicate that falling water levels over the period were not determined by climate alone. Trends in monthly evaporation amounts indicated a very small decrease in recent times with no effect on lake levels. Monthly averages showed a strong variability in monthly rainfall and exhibited marked differences in variability among individual months. This means that the input of water into the lake from rainfall varied according to the wetness of the month, but long-term trends cannot predict changes in lake levels. In the source area of rivers, stream flow was mainly determined by rainfall amount. As the rivers approach the lake, other factors were involved making it impossible to predict stream discharge by rainfall amounts alone. Factors responsible for this include both surface and sub-surface abstractions and damming of rivers draining into the lake. Encroachment of forest areas within the catchment area of the lake by settlement and irrigation of crops along the rivers also affected water levels indirectly. Eroded topsoil was deposited along river channels and in the lake itself, hence reducing its capacity.