El Niño threatens food crop yields

16 May 2014 by Alex Peel

Major disruption to global weather patterns triggered by El Niño events can reduce global yields of important food crops, say scientists.

Graphic showing Pacific Ocean temperaturesNew research, published in Nature Communications, assesses the effect of the climate phenomenon on global yields of maize, wheat, rice and soybean.

Together these plants are responsible for around 60 per cent of the world's food calories produced on croplands.

The study finds that soybean yields are improved in El Niño years by as much as 5 per cent. But global yields of rice, wheat and maize are changed in the range of -4.3 to +0.8 per cent.

The researchers hope the work will help governments to plan ahead when an El Niño is on the way.

"This new work tells us that we can predict when the bad years will be, ahead of the harvest," says study co-author Professor Andy Challinor, from the University of Leeds.

"The study shows that measures need to be taken to safeguard food supply in bad years and also to make the most of good years."

El Niño events occur as part of a cycle of warming and cooling from one side of the Pacific Ocean to the other. It's driven by the complex relationship between the region's winds, sea-surface temperatures, and ocean currents.

The extra heat and moisture in the region can trigger global disruption to rainfall patterns, bringing devastating floods and droughts to every continent, and an upsurge in tropical cyclones in the eastern Pacific.

We need to pay more attention to La Niña from a food trade point of view.

- Dr Toshichika Iizumi

Its sister phenomenon, La Niña, sees a cooling of temperatures in the eastern Pacific, but increased heat and moisture in the west. Together, they're known as the El Niño Southern Oscillation (ENSO).

The researchers found that the negative effects of La Niña on crop yields were less widespread than El Niño, but it also affected fewer areas positively. Altogether, La Niña was found to reduce global yields of all four crops, in the range of -4.5 to 0 per cent.

"The El Niño remains a concern for regions where crop production is negatively affected," says Dr Toshichika Iizumi, from the National Institute for Agro-Environmental Sciences in Japan, who led the study. "But we need to pay more attention to La Niña from a food trade point of view."

Recent satellite measurements of conditions in the eastern Pacific suggest that an El Niño could be on the way in 2014, and there are early signs that it could be similar in intensity to the powerful 1997 event.

That event saw sea surface temperatures of more than 28°C develop in the normally cold and dry eastern Pacific. The resulting disruption to global weather claimed an estimated 2,100 lives, and caused US $35-45 billion in damage.

A recent study suggested that global warming will cause El Niños to become more intense. And another predicted that the frequency of extreme events, like the one in 1997, will double over the coming century.

'Impacts of El Niño Southern Oscillation on the global yields of major crops' - Toshichika Iizumi, Jing-Jia Luo, Andrew J Challinor, Gen Sakurai, Masayuki Yokozawa, Hirofumi Sakuma, Molly E Brown, & Toshio Yamagata, 2014, Nature Communications.