East African droughts linked to cooler Pacific Ocean

Severity of African droughts
Copyright: NASA/JPL AIRS Project

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  • The droughts have previously been linked to increased global warming
  • A study shows they may result from cool temperatures in the Pacific Ocean
  • But the study fails to explain severity and frequency of droughts, says an expert

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[NAIROBI] Frequent droughts in East Africa have been linked to cooler sea surface temperatures in the tropical Pacific Ocean, a modelling study shows, contradicting the expectation that they were due to global warming.

Researchers from the US-based International Research Institute for Climate and Society (IRI) at Columbia University say that the increase in droughts in East Africa since 1999 was linked to changes in sea surface temperatures in the Pacific Ocean .

They removed the influences of global warming and long-term sea surface temperatures from climate change data sets and estimated changes in atmospheric conditions for the period 1900-2012 to determine if short-term droughts that occur from March to May could be present in the absence of those factors.

The researchers found similar atmospheric conditions despite removing those factors, according to the study published in Climate Dynamics on 26 July.
The study's lead author, Bradfield Lyon, a climate research scientist at IRI, tells SciDev.Net that using observational data and climate model simulations, they provide clear evidence that the drought increase is primarily from slowly varying natural variations in sea surface temperatures. 
"The changes in sea surface temperatures in the Pacific occurred abruptly in 1999, which coincided with the increase in drought in East Africa at that time.  Anthropogenic ― human made ― climate change was not found to be playing a major role," he says.   
According to Lyon, the findings imply that in the future, when sea surface temperatures in the tropical Pacific switch back to warmer conditions, rainfall will likely increase in East Africa but if the temperatures remain cooler than average the likelihood of drought is enhanced.
James Kinyangi, regional program leader for East Africa, CGIAR’s Research Program on Climate Change, Agriculture and Food Security (CCAFS), says there is a need for caution in interpreting the link to drought events because these are regional and  is fraught with uncertainty.
"The paper does not adequately address the uncertainty associated with this observational series. This variability does not explain why drought events are becoming more frequent and severe," Kinyangi tells SciDev.Net.
Richard Odingo, a former vice-chairperson of the Intergovernmental Panel on Climate Change, says the study’s finding is contrary to what is known.
"Frequent droughts [in East Africa] are partly linked to [warmer] sea surface temperatures in the Indian Ocean," says Odingo.

Link to full paper in Climate Dynamics
This article has been produced by SciDev.Net’s Sub-Saharan Africa desk.


Climate Dynamics doi: 10.1007/s00382-013-1891-9 (2013)