A strong link has been confirmed between sea surface temperatures and precipitation in Africa’s semi-arid Sahel, according to a new study published in Science on October 9th. The study was co-authored by Alessandra Giannini, a climate expert with the International Research Institute for Climate Prediction (IRI), a unit of the Earth Institute at Columbia University.
The time series in the figure above represents variations above or below the long-term mean of rainfall in the Sahel region of Africa (located just south of the Sahara, between 10N and 20N). The observed time series is the average of station observations in the region, while the modeled time series is an areal average of the models rendition of the variability. The similarity between the two is a measure of the success of the model in reproducing the observed variability, based on the influence of sea surface temperatures only on the global atmospheric circulation, and on Sahel rainfall. Image credit: Alessandra Giannini
Previously, it was not known how much land use changes may have led to the region’s recent history of prolonged drought, or whether variability in ocean temperatures was the primary driver of the region’s climate. The new study finds that “pervasive evidence” indicates that sea surface temperatures, particularly in the Indian Ocean, are the most powerful indicators of precipitation in the Sahel.
Tropical Pacific surface temperature variation, such as that occurring with the El Niño and Southern Oscillation phenomena, have an effect on the variation of year-to-year rainfall, while the Indian and possibly Atlantic Oceans, affect longer term trends. The new study tracked sea surface temperatures and precipitation rates from 1930-2000, the first time that ocean and climate trends have been studies on a decadal time scale.
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