Lake-effect rainfall over Africa’s great lakes and other lakes in the rift valleys

Abstract

This article examines rainfall over 27 lakes in eastern Africa and compares this to rainfall over the lakes' catchments or surrounding regions, using the TRMM 3B43 and 3B42 satellite rainfall products. A comparison is made for annual rainfall and for rainfall in each month. The diurnal cycle of rainfall is also examined over the lakes and over the catchments/surrounding regions. It is shown that rainfall is enhanced over nearly all lakes and in all months. Contrasts between over-lake and catchment rainfall are greatest at night and during the dry months. For the smaller lakes the enhancement is apparent in both nocturnal and daytime rainfall. Over the largest lakes (Victoria, Tanganyika, Malawi) a single rainfall maximum occurs at night and rainfall is generally lower over the lake than over the catchment during the day. The majority of the other lakes have a bimodal rainfall maximum, with a strong peak between 03 and 09 LST and a second peak most generally at 18 LST. The daytime maximum over the lakes might represent a drift of land systems over the lake, but humidity over the lake appears to play a role as well. Except for the large lakes, there is strong uniformity in the times of maximum and minimum rainfall (18 LST and 12 LST, respectively) over both the lakes and the catchments. Nocturnal rainfall is common over both the lakes and the catchments. Nocturnal rainfall over the land might be a drift of the systems generated over the lakes.