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A climate model-based review of drought in the Sahel: Desertification, the re-greening and climate change

The Sahel is a vast semiarid region immediately south of the Sahara that has endured decades of decreased rainfall and creeping desertification. This paper supports an ocean-mediated model for climate change in the Sahel in contrast to older models which focus on localized human activity. "We review the evidence that connects drought and desertification in the Sahel with climate change past, present and future. Advances in climate modeling point to the oceans, not land, as the cause of the recent persistence of drought in the Sahel. The current generation of global climate models reproduces the spatial extent, continental in scale, and the timing and duration of the shift to dry conditions that occurred in the late 1960's given knowledge of observed surface oceanic conditions only. The pattern statistically and dynamically associated with drought is one of warming of the tropical oceans, especially the Pacific and Indian Oceans, superimposed on an enhanced warming of the southern compared to the northern hemisphere most evident in the Atlantic. These models, which include a prognostic description of land surface and/or vegetation, albeit crude, indicate that positive feedbacks between precipitation and land surface/cover may act to amplify the ocean-forced component of continental climate. Despite the advances made in understanding the recent past, uncertainty dominates as we move forward in time, to the present, partial greening of the Sahel, and to the future of climate change projections." Older models emphasize the role of deforestation and overfarming in the drought patterns, but new models point to warming equatorial oceans as a more likely culprit. However, the long-term affects for the Sahel are uncertain, and possible outcomes range from total desertification to a partial greening.
Alessandra Giannini et al
The Earth Institute at Columbia University
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