Rising warmer global temperature averages have corresponded with wetter rainy seasons in East Africa in October and November. But having more moisture in the warmer atmosphere doesn't help plant growth if strong La Niña winds keep periodically blowing the moisture elsewhere.
A cool period from 18,000 to 21,000 years ago correlated with drier, but more stable conditions in East Africa. So although the rainy seasons may have been drier, they were dependable.
"Even though rainfall did not vary much during that period, the sediment layers still reflect the beat of El Niño and La Niña cycles," said co-author Axel Timmermann, of the University of Hawaii at Manoa. "Compared with this coldest time, the last 3,000 years have been wetter but more variable, with severe century-long droughts sprinkled throughout."
The increased variability has made it hard for farmers, herders and wildlife to prepare for the next year.
"Will these projected changes affect East Africa's unique biodiversity in its national parks, such as the Serengeti?" asks Timmermann. "We do not yet know, but there are fascinating links to explore further."