A large proportion of people living in this swath of countries at the southern end of the Sahara are subsistence farmers; without the rains their crops fail and their animals die. In recent years the climate has been reliable, but what does the future hold? To answer this question Benjamin Sultan from the Sorbonne Universités in Paris, and colleagues from Stanford University and Columbia University in the US used nine bias-corrected climate models from the Coupled Model Intercomparison Project (CMIP5) and two crop models (SARRA-H and APSIM) to evaluate the likely impact of climate change on the yield of sorghum, one of the staple crops in this area.

The researchers’ bias-corrected models were in broad agreement with the full CMIP5 ensemble, projecting a warming of 2.8 °C by the decades 2031–2060 compared with a baseline average for 1961–1990. They also showed that a robust change in rainfall is expected, with less rain in the western part of the Sahel (Senegal and southwest Mali) and more rain in central Sahel (Burkina Faso and southwest Niger). What’s more, they note a shift in seasonality of the monsoon, with the rainfall deficits in the western Sahel tending to occur early in the season, while the rainfall increases are likely to come during the late part of the monsoon season.

So what impact will these climate changes have on sorghum? The models suggest that average yield will fall by as much as one fifth, with the greatest losses in the western Sahel. “This is because of the adverse role of higher temperatures in shortening the crop-cycle duration and increasing evapotranspiration demand, thus reducing crop yields,” said Sultan. Even the increase in rainfall in the central Sahel region fails to counteract the detrimental effect of higher temperatures.

A reduction in yield seems inevitable, but there are ways of mitigating the impact. In particular Sultan and his colleagues showed that modern cultivars of sorghum were more resilient to the expected climate change.

“Modern cultivars tend to have a short growth cycle and these short-duration varieties will be better adapted to the short rainy seasons of the future,” said Sultan.

Meanwhile, the increase in carbon dioxide in the atmosphere is expected to offset the negative climate impact on sorghum yield by around 10%. Nonetheless, the net impact of climate change across West Africa will still be negative; Sultan and his colleagues warn that the reduction in rainfall and subsequent fall in sorghum yield could be similar to that experienced during the severe droughts of the 1980s – a time that no-one in the region wants to return to.

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