Tuesday, June 25, 2013

A simple explanation for the complex climate variations in the Sahel

Alessandra Giannini in Environmental Research Web: A recent article in Environmental Research Letters (ERL) provides a simple interpretation of how the oceans influence the climate in the Sahel. The analysis makes sense of past droughts and the current trends towards increased rainfall, consistent with near- and long-term model projections.

...Drought came about abruptly in the Sahel in the early 1970s and scientists studying its cause focused on local factors. They postulated that rapid population growth had led to extensive farming and that degradation of marginal land had engendered drought – something that further degraded vegetation cover in the region.

In recent years drought in the Sahel has alternated with flooding and desertification has been replaced by re-greening. An alternative explanation relating the evolution of the Sahelian climate to global rather than local influence has gained ground. This influence is the oceans, the dominant source of moisture for semi-arid regions like the Sahel.

Our article provides a simple interpretation of the influence of the oceans on the Sahel, one that makes sense of past drought and of the current trend towards increased rainfall in near- and long-term projections.

...In the case of the Sahel, the global tropical sea-surface temperature average provides a quantitative estimate of the influence on deep convection, while the local North Atlantic average provides an estimate of the increase in moisture. The two can evolve independently but it is the difference between them that matters when it comes to predicting Sahel rains...

The Bandiagara Cliffs in the Dogon region of Mali, shot by Personnel, Wikimedia Commons, public domain

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