ADDIS ABEBA – Sorghum yields in the Ethiopian highlands could decrease as intense El Niño events become more common, researchers say.
Climate change is expected to increase the region’s rainfall overall but droughts are likely to become more prevalent early in the growing season when crops are vulnerable.
The researchers acknowledge uncertainty around the precise pattern of the changes.
But their predictions indicate that sorghum yields in the worst-affected years could fall by as much as 40%—an effect that is overlooked by studies that focus only on annual changes.
To assess the influence of drought on sorghum yields, Michael Eggen of the University of Wisconsin Madison in the US and colleagues employed a computer model that links plant growth to weather conditions.
The simulations showed that, though robust to rainfall deficits at the seasonal scale, sorghum yields are acutely sensitive to water shortages in June, when seeds are planted and early growth takes place.
The researchers combined the simulation results with climate forecasts from 14 general circulation models chosen for how well they relate rainfall in the Ethiopian highlands to the El Niño Southern Oscillation.
The researchers applied the models to two scenarios: one in which the concentration of carbon dioxide in the atmosphere levels off at around 600 parts per million (ppm), and one in which it rises to well over 1000 ppm by 2100.
The models suggested that, in general, precipitation in the Ethiopian highlands will rise over the course of the century, but June droughts will become more prevalent. Temperatures will also increase, although their effect on sorghum yield is likely to be small compared to the changes in early-season rainfall.
“Somewhat higher temperatures are not necessarily a major problem if they are accompanied by higher rainfall,” says Eggen. “What our study shows is that it is really those extreme dry June events that could lead to catastrophically lower yields.”
Caption: A farmer plows his sorghum field to plant again after early rains failed. (Photo Zaitchik)