El Nino/La Nina can help forecast crop yields

COLUMBIA, Mo.–Water temperatures in the tropical Pacific can end up having a lot to do with the price of corn in Missouri, thanks to El Nino and La Nina, says a University of Missouri atmospheric scientist.

El Nino is what atmospheric scientists call the recurring period of warmer than normal waters in the equatorial Pacific. This period can persist for two to seven years, and it affects weather in different ways in different parts of the world.

In the American Midwest, the transition to El Nino tends to bring milder summers with more regular rainfall, says Tony Lupo, professor and chair of the MU Department of Soil, Environmental and Atmospheric Sciences.

By contrast, the transition to La Nina—a period of cooling waters in the eastern equatorial Pacific—tends to bring the Midwest hot summers and irregular rainfall. There are also “neutral” periods of normal water temperatures. The whole cycle is called the El Nino-Southern Oscillation (ENSO).

Lupo says a weak La Nina played a role in the devastating drought of 2012. That summer was marked by high temperatures and sparse rain. As is typical for La Nina years, the rains that did come tended to be brief, heavy downpours, dropping lots of water so quickly that much of the rain was lost as runoff.

Atmospheric scientists have long thought that El Nino and La Nina usually don’t have a major direct effect on crop yields in the United States, except in extreme cases such as the 2012 drought. El Nino is at peak strength in winter and weak in the summer, when U.S. crops are growing. In addition, yields per acre have generally gone up from year to year as technology advanced. So weather variations from ENSO, many assumed, were unlikely to make much difference.

However, a close look at historical data for crop yields in Missouri suggests otherwise, says Lupo.

One of his students, Jessica Donovan, a sophomore in MU’s College of Agriculture, Food and Natural Resources, analyzed harvest records for corn, soybean and wheat back to 1920. Controlling for the effects of technology on yields, Donovan found a definite correlation between El Nina/La Nina and Missouri’s corn and soybean yields.

“We’re finding that when it’s transitioning into El Nino years, the corn yields are higher,” Donovan says. “Then when it’s transitioning into La Nina, the corn crops don’t have as high yields.”

The same is true of soybean, though the effect is not as strong as with corn, she says. Soybean plants have deeper roots than corn, and so are less vulnerable to variations in temperature and precipitation.

“The research we’re doing—trying to link El Nino-La Nina weather cycles to corn and soybean yields—would give some ability to anticipate these things two to four seasons in advance,” says Lupo.

That would help many people in agriculture-related fields make decisions and manage risk. It could help farmers decide what to plant or whether to invest in particular technologies. Accurate long-range forecasts would also aid farm commodity traders, businesses, policymakers and others.

The catch is that El Nino and La Nina don’t follow a set schedule, and they can vary in duration and strength. Other events in the atmosphere and the oceans also can play a role in a particular region’s weather.  But Lupo says that growing understanding of ENSO and other weather cycles, combined with increasingly sophisticated computer models, is dramatically improving the reliability of long-range weather forecasting.

“Some of the leading research on long-range forecasting is not only getting the El Nino cycle down, but even the decadal-scale cycles that impact the strength of El Nino,” he says. “Soon we’re going to have the ability to get general predictions as much as 20 years in advance.”