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November 12, 2008 | Lake Victoria's water levels reached a 40-year low in 2006 when East Africa was gripped by drought. The largest lake in Africa, Victoria provides food, transport, and electricity to more than 30 million Kenyans, Tanzanians, and Ugandans—making its health a matter of great concern.
The lake's outlet is controlled by Uganda, which operates the Owen Falls (Nalubaale) Dam for hydroelectric power. In 2006, United Nations officials charged that Uganda was drawing more of the lake's water than was agreed upon under an international pact; Ugandan authorities blamed the drought and said that all lakes in the region had declining water levels.
A study by Sean Swenson, a NCAR postdoctoral researcher, shows that drought was not the only cause of Lake Victoria's shrinkage—human management at the dam was also to blame.
For his study, Sean and a colleague drew on data from GRACE (Gravity Recovery and Climate Experiment), twin satellites that measure Earth's gravity field, to measure the total mass of water in the region around Lake Victoria. He also used data from satellite altimeters to look at water levels in a number of lakes in the region. By combining data sets, he was able to compare changes in Lake Victoria to hydrological changes in the region as a whole, thereby separating the effects of climate from the influence of the dams.
Sean found that Lake Victoria diverged from other lakes in the region, which showed a consistent response to the drought. "Lake Victoria dropped much more rapidly than the surrounding regions, implicating the human control on the lake as the cause," he says.
Sean's study serves as an independent assessment of Lake Victoria's water balance. It also provides a baseline for future research on the region's hydrology.