The water balance of the East African Great Lakes.
The East African Great Lakes are important indicators of climatic and environmental change
in an area where standard meteorological data are scarce. Three large lakes, Lakes Victoria,
Tanganyika and Malawi are studied in order to build water balance relations between lake
level and over-lake rainfall. By analyzing the satellite observations, the characteristics
of the regional and mesoscale circulations are studied through analysis of convective
activity and cloudiness over the lakes. Using a regression approach, the relationship
between catchment rainfall and cold cloud frequency is found. Assuming the same convective
mechanism operates for each lake and its catchment, the over-lake rainfall is calculated
using the catchment rainfall, which has long records. Evaporation is estimated for each
lake by energy-budget and Penman methods and a sensitivity study is also carried out. The
available tributary inflow and lake outflow data of Lake Victoria are expressed by rainfall
and lake level terms. For Lake Victoria, the water balance model is reformulated as a lake
level model. The model is first used to predict the lake level changes as a validation. Then
it is inverted so that the over-lake rainfall can be reconstructed from known lake levels in
both modern times and historical times. In modern times, the precision is on the order of 1%
for the calculated mean rainfall and a few percent for the calculated annual rainfall.