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[NAIROBI] Researchers in the United States have found a link between low rainfall in East Africa during the March-May rainy season, and changes in sea surface temperature in the tropical Pacific Ocean.

The region endured a catastrophic drought last year. The lack of rain in 2010 during the October-December rain season — known as the 'short rains' — was widely anticipated due to an established link between these rains and El Niño and La Niña events.

But researchers say last year's failure of the region's other key rains — the so-called 'long rains', which tend to fall between March and May – was much harder to anticipate.

"Historically, the long rains have not shown a strong relationship to El Niño and La Niña the way the short rains do," Bradfield Lyon, a co-author of the study and climate scientist at Columbia University's International Research Institute for Climate and Society, told SciDev.Net.

Lyon and colleague David DeWitt have now identified a link between the 'long rains' and ocean temperatures in the Pacific.

They noted that in 1999, there was an abrupt change in Pacific ocean surface temperatures. The western Pacific surface became warmer, while surface temperatures in the eastern Pacific became cooler. Historical climate observations were combined with climate model experiments, and the authors concluded that these changes were strongly linked to "a similarly abrupt decline in East African long rains that occurred around that time".

Their findings were published in Geophysical Research Letters in January.

The researchers did not find an explanation for the change in ocean temperatures. And long-term climate change, which their study did not address, "may further complicate the picture", Lyon said.

They also warn that the disruption to the 'long rains' may continue for a few more years.

"The slowly varying nature of these ocean conditions suggests that the current pattern may persist for several years to come," Lyon said, although he added there may be variations from one year to the next.

Chris Funk, a climatologist with the Famine Early Warning Systems Network (FEWS NET), told SciDev.Net this was "an excellent study".

The paper "makes an eloquent case that it has really been changes in the central–western Pacific that have been most important" in affecting the long rains, he said, adding "it will likely lead to improved forecasts".

Funk said his own research, motivated by the study, had shown that seven of the past eight failed 'long rains' were linked to Pacific sea temperatures.

"This research is already influencing climate forecasting and food security preparedness in a positive way," he added.

Link to abstract in Geophysical Research Letters

Additional reporting by Mićo Tatalović


Geophysical Research Letters doi:10.1029/2011GL050337 (2012)