By Malee Oot January 17, 2014
Decreased rainfall and frequent dry events have plagued communities across East Africa in the last decade.¹ For example, in 2011, the most severe drought in 60 years cost nearly 100,000 lives in Ethiopia, Kenya and Somalia, according Britain’s development agency DFID. Half of the casualties were children, with nearly 29,000 dying in just 90 days between March and June of 2011, based on US government data. The 2011 drought also destroyed livelihoods and market systems across the region, affecting at many as 13 million people, according to the U.S. Agency for International Development (USAID).
Now, a new study from the Climate Hazards Group at the University of California, Santa Barbara (UCSB) is linking these devastating declines in East African precipitation to rapidly rising sea surface temperatures in the Indo-Pacific Ocean.²
The UCSB study, published in the journal Climate Dynamics, used simulations to evaluate if fluctuations in precipitation levels over the last decade in East Africa were the result of El Niño-like events, or, linked to other anomalies, such as rising sea surface temperatures in the western Pacific Ocean.
Dr. Andy Hoell, one of the lead authors of the UCSB study told the U.S. Agency for International Development’s interview blog series Behind the Scenes, “The way we posed our study was to understand if El Niño Southern Oscillation over the central Pacific Ocean was the main reason for it [decreased rainfall over East Africa]—and while El Niño Southern Oscillation certainly has an impact over East Africa, it wasn’t the main cause. What the main cause was—was warming sea surface temperatures over the west Pacific.”
The UCSB study first looked at data on climate and precipitation in East Africa since 1999; and at the behavior of sea surface temperatures in the Indo-Pacific during the same period. Based on rainfall patterns in East Africa and sea surface temperature trends in the Indo-Pacific, the researchers were able to initially prove what Dr. Hoell termed a ‘superficial’ connection.
In the second part of the study, researchers used atmospheric models to simulate both the impact of El Niño Southern Oscillation and rapidly rising sea surface temperatures in the Indo-Pacific. Based on the simulations, researchers were able to discern the forcing of East African precipitation was being influenced by more than just the El Niño Southern Oscillation.
Dr. Hoell explained to Behind the Scenes, “Since 1950 there has been a slight increase in the west Pacific sea surface temperatures…but from 1999 to 2012 we have seen very large increases in those sea surface temperatures. The mechanism we understand to be occurring here is that warm air rising over the Maritime [or the Indonesian continent], then rises and spreads away from that region and then subsides or sinks over eastern Africa thereby decreasing rainfall.” Generally, sinking air is dry and produces little if any precipitation.