Sorghum yields in Ethiopia’s highlands could fall by as much as 40 percent in the worst years as strong El Niño events become more common, a team of US and Ethiopian researchers has found.
A sorghum field on the shore of Lake Hayq, Ethiopia, November 2012 (Radosław Botev, Wikimedia Commons, CC BY 3.0 PL) [file photo]
Climate change is expected to bring the region more rain overall, according to Physics World, but droughts are likely to become more frequent early in the growing season, when the crop is most vulnerable, and that effect is missed by studies that look only at yearly totals.
Michael Eggen of the University of Wisconsin–Madison and his colleagues used a computer model that links plant growth to the weather. It showed that sorghum copes well with a dry season as a whole but is acutely sensitive to water shortages in June, when seeds are planted and the young plants establish. Such conditions occurred in 2015, when a strong El Niño produced harvests that farmers consider as bad as, or worse than, those of the famines of the 1980s and 1990s.
The team combined these results with forecasts from 14 climate models, chosen for how well they link highland rainfall to the El Niño Southern Oscillation, under two scenarios: carbon dioxide levelling off at around 600 parts per million, or rising to well over 1,000 parts per million by 2100. The models suggested that rainfall in the highlands will rise over the century but that June droughts will become more common. Higher temperatures are likely to matter much less than early-season rain. “What our study shows is that it is really those extreme dry June events that could lead to catastrophically lower yields,” Eggen said.
Sorghum is a drought-resistant grass that grows in poor soils where fertilizer is too costly, which makes it a staple for small farms across sub-Saharan Africa. Because it is so hardy, farmers tend to keep planting it even when dry Junes kill the seedlings, which leaves few ways to avoid shortages in strong El Niño years.
The researchers suggest breeding or adopting varieties that can survive dry spells in June, either through drought tolerance or by growing faster so they can be planted later. “The problem with shorter season varieties is they often need more inputs to deliver similar yields in the shorter time frame,” Eggen said. “More drought-tolerant varieties might exist, because sorghum is grown in drier parts of Ethiopia and Sudan.”
The findings were published in the journal Environmental Research Letters.
Sources: Physics World