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Study Finds Long History Of El Niño In East Africa

August 6, 2011

A new study published in the Friday edition of the journal Science has found that East Africa has been affected by the ENSO phenomenon (El Niño Southern Oscillation) known as El Niño/La Niña for more than 20,000 years.

The work, which was completed by scientists from Germany, Switzerland, the US, the Netherlands, and Belgium, studied Lake Challa, a crater lake near Mt. Kilimanjaro. According to a press release from the University of Hawaii School of Ocean and Earth Science and Technology (SOEST), which participated in the research, the mud found at the lake’s bottom shows yearly layers of sedimentation that vary in color and thickness, and “reflect ENSO behavior.”

“During the cold phase of La Niña, there is marginal rainfall and stronger winds in East Africa, while the El Niño warm phase leads to weak wind conditions with frequent rain,” noted a second press release, this one from the Helmholtz Association of German Research Centers. “Moreover, during the coldest period of the last ice age about 18 000 to 21 000 years ago, East Africa’s climate was relatively stable and dry.”

Currently, the researchers said, many locations throughout Kenya, Ethiopia, Djibouti and Somalia are in the midst of a “catastrophic drought” attributed to La Niña that lasted from June 2010 through May of this year in the Pacific. As a result, food security in these areas is threatened, and millions of people require assistance immediately, the University of Hawaii press release states.

“During La Niña, rainfall is sparse and the winds over Lake Challa are strong,” author Christian Wolff of the University of Potsdam, Germany, said in a statement. “The winds enhance upwelling of nutrients, intensifying the seasonal blooms of algae. After dying and sinking, they form thick layers of light-colored sediments. During El Niño events, on the other hand, rainfall is frequent and the winds are weak, resulting in thinner white layers in the sediment.”

The scientists claim that their findings “fit the growing consensus” that global warming will eventually have a large-scale impact on rainfall patterns, and that their observations are consistent with 21st century climate-based computer models simulating the development of East Africa in response to increased greenhouse gas levels. They believe that the rainy period, which currently lasts from October to November, could ultimately get even shorter as the temperatures increase and the atmosphere begins to hold more water.

“Will these projected changes affect East Africa’s unique biodiversity in its national parks, such as the Serengeti?” We do not yet know, but there are fascinating links to explore further,” added co-author Axel Timmermann, Professor at the University of Hawaii’s International Pacific Research Center and the School of Ocean and Earth Science and Technology.

Image Caption: Lake Challa with Mt. Kilimanjaro in the background. The white speck on the lake is the sediment-core drilling platform. Credit: Photo courtesy Stephan Opitz

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