Indian Ocean climate event brings floods to East Africa's lakes and the Sudd marsh

During an El Nino, the expected rainfall increase over most of the Lake Vic toria catchment area is similar to 15-25%. However, due to anomalous warmin g of the western equatorial Indian Ocean during 1997, strong convection dev eloped over parts of the Horn and eastern Africa. This resulted in a much l arger 20-160% precipitation excess during the "short rainy" season. Satelli te radar altimetry data reveals that not only did Lake Victoria rise by sim ilar to 1.7 m, but that the rainfall event similarly affected lakes Tangany ika, Malawi and Turkana. In addition, the seasonal level minima of the Sudd marshes and Lakes T'ana and Nasser continue to increase. Such a rainfall e vent will have severe, longterm consequences for the natural surface flows and storages along the White Nile. Based on the hydrological impacts of the historic 1961 East Africa event, we can expect the current high levels of Lake Victoria to be maintained for the remainder of this decade. In additio n, we anticipate a major expansion of the permanent swamp regions of the Su dd marshes over the forthcoming seasons. Blue Nile flows, further enhanced by the above-average 1998 rainfall season, can also be expected to remain h igh, at least until early 1999.