Abstract
Summer rainfall in the Sahel region of Africa exhibits one of the largest signals of climatic variability and with a population reliant on agricultural productivity, the Sahel is particularly vulnerable to major droughts such as occurred in the 1970s and 1980s. Rainfall levels have subsequently recovered, but future projections remain uncertain. Here we show that Sahel rainfall is skilfully predicted on inter-annual and multi-year (that is, >5 years) timescales and use these predictions to better understand the driving mechanisms. Moisture budget analysis indicates that on multi-year timescales, a warmer north Atlantic and Mediterranean enhance Sahel rainfall through increased meridional convergence of low-level, externally sourced moisture. In contrast, year-to-year rainfall levels are largely determined by the recycling rate of local moisture, regulated by planetary circulation patterns associated with the El Niño-Southern Oscillation. Our findings aid improved understanding and forecasting of Sahel drought, paramount for successful adaptation strategies in a changing climate.
Highlights
Summer rainfall in the Sahel region of Africa exhibits one of the largest signals of climatic variability and with a population reliant on agricultural productivity, the Sahel is vulnerable to major droughts such as occurred in the 1970s and 1980s
We have shown that Sahel rainfall and the associated driving mechanisms are predictable on both multi-year and inter-annual timescales
We investigate the lack of rainfall in DePreSys[3] by analysing the first empirical orthogonal function (EOF1) for Sahel precipitation, which accounts for B30% of the variance in both the observations and DePreSys[3]
Summary
Summer rainfall in the Sahel region of Africa exhibits one of the largest signals of climatic variability and with a population reliant on agricultural productivity, the Sahel is vulnerable to major droughts such as occurred in the 1970s and 1980s. We show that Sahel rainfall is skilfully predicted on inter-annual and multi-year (that is, 45 years) timescales and use these predictions to better understand the driving mechanisms. Sahelian summer rainfall has since recovered to the levels of the 1960s3, but future projections are uncertain[5] Superimposed on this multi-decadal change are substantial swings in inter-annual rainfall levels[2]. Understanding the physical drivers of both inter-annual and multi-year Sahelian rainfall variability is crucial to gain confidence in future predictions. We present improved understanding and prediction of Sahel rainfall variability on both multi-year and inter-annual timescales for lead times 48 months, using a comprehensive set of retrospective forecasts (hereafter hindcasts) from the latest Met Office Decadal Climate Prediction system, DePreSys[3] Covering the period since 1960, DePreSys[3] uses a much higher resolution (B60 km in the atmosphere and 0.25° in the ocean) than previous versions[23,24], enabling better representation of the key physical processes[25] (Methods)
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