Hotter Sahara could mean more rain for Sahel
Rising temperatures in the Sahara desert could reduce drought in the Sahel region immediately south of it, say researchers.
The findings, published in Geophysical Research Letters this month (10 September), add to a growing body of research on how climate change might affect the continent.
Reindert Haarsma and colleagues of the Royal Netherlands Meteorological Institute used a computer model to predict the effects of rising temperatures on rainfall over Africa. They say their study is the first to consider the roles of both land and sea surface temperatures.
The model suggests that if emissions of greenhouse gases are not reduced, higher temperatures over the Sahara would cause 1-2 millimetres of extra daily rainfall in the Sahel by 2080 during the months from July to September.
This might seem small, but it is 25 to 50 per cent more than fell in the drought-prone region in 1980.
The Sahel stretches from Senegal to Somalia and encompasses large parts of Mali, Mauritania and Niger, where drought — together with locusts — caused a major famine this year.
In June, US-based scientists published research that also suggested climate change could increase rainfall in the Sahel (see Decades of drought predicted for southern Africa).
That study indicated that changes in the temperature of the Atlantic Ocean would cause more rain, but it did not consider the role of temperature change on the continent itself.
In contrast, Haarsma's team found it was mainly due to a hotter Sahara.
He explains that the Sahara heats up faster than the oceans, creating lower atmospheric pressure above the desert. This in turn leads to more moisture moving in from the Atlantic to the Sahel.
However, Haarsma told SciDev.Net that unlike the research published in June, his study used only one model. This means the results need to be confirmed by further studies already underway.
Speaking to the UK newspaper The Guardian, Peter Cox of the UK-based Centre for Ecology and Hydrology said the study was interesting, but warned that "the conclusion that Sahelian rainfall will increase under climate change must be considered as highly uncertain".
"Models differ in their predictions, with about as many showing decreases in rainfall as increases."
Reference: Geophysical Research Letters doi 10.1029/2005GL023232 (2005)
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