Multiyear La Niña Events and Multiseason Drought in the Horn of Africa

Anderson, Weston; Cook, Benjamin I.; Slinski, Kim; McNally, Amy; Funk, Chris

One of the primary sources of predictability for seasonal hydroclimate forecasts are sea surface temperatures (SSTs) in the tropical Pacific, including El Nin˜ o–Southern Oscillation. Multiyear La Nin˜ a events in particular may be both predictable at long lead times and favor drought in the bimodal rainfall regions of East Africa. However, SST patterns in the tropical Pacific and adjacent ocean basins often differ substantially between first- and second-year La Nin˜ as, which can change how these events affect regional climate. Here, we demonstrate that multiyear La Nin˜ a events favor drought in the Horn of Africa in three consecutive seasons [October–December (OND), March–May (MAM), OND]. But they do not tend to increase the probability of a fourth season of drought owing to the sea surface temperatures and associated atmospheric teleconnections in the MAM long rains season following second-year La Nin˜ a events. First-year La Nin˜ as tend to have both greater subsidence over the Horn of Africa, associated with warmer waters in the west Pacific that enhance the Walker circulation, and greater cross-continental moisture transport, associated with a warm tropical Atlantic, as compared to second-year La Nin˜ as. Both the increased subsidence and enhanced cross-continental moisture transport favors drought in the Horn of Africa. Our results provide a physical understanding of the sources and limitations of predictability for using multiyear La Nin˜ a forecasts to predict drought in the Horn of Africa.


Also Published In

Journal of Hydrometeorology
American Meteorological Society

More About This Work

Academic Units
International Research Institute for Climate and Society
Published Here
March 13, 2024

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