Climate Fact: East African Rains and the Tropical Pacific
In Brief: The recent weakness in the East African long rains has been linked to persistently elevated temperatures in the western tropical Pacific.
Rains in East Africa primarily fall during the long rains (March through May) and the short rains (October through December). Understanding how climate and climate change influence these rains is particularly important for predicting drought in the region. Conditions in the tropical Pacific affect weather throughout the world and the tendency for the tropical Pacific to persist in either cool La Niña phases or warm El Niño phases enable forecasters to predict whether seasonal temperatures or precipitation levels will be above or below average. In addition to local Indian Ocean sea surface temperatures, the short rains in East Africa are strongly influenced by conditions in the tropical Pacific, with La Niña phases leading to reduced precipitation. How the tropical Pacific affects the long rain season, on the other hand, is harder to identify. Recent work shows that since 1999, the long rains have been consistently weak and unable to compensate for reduced short rain precipitation during La Niña phases, leading to drought conditions like those experienced in 2011. Also since 1999, there has been a pattern of consistently elevated sea surface temperatures in the western tropical Pacific and consistently high rainfall levels in that region. The tendency of ocean surface temperatures to remain in particularly warm or cool conditions for relatively long periods of time, coupled with what is known about the atmospheric links between the western tropical Pacific and East Africa, enables forecasters to better understand and predict droughts there.
Seasons: Winter, Spring, Summer, Fall
Source: Lynn, B and DeWiltt, DG. “A recent and abrupt decline in the East African long rains.” Geophysical Research Letters 39 (2012): L02702.
