El Niño/La Niña can help forecast crop yields
Water temperatures in the tropical Pacific can end up having a lot to do with the price of corn in Missouri, thanks to El Niño and La Niña, says a University of Missouri atmospheric scientist.
El Niño 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 Niño 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 Niña -- 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 Niño-Southern Oscillation (ENSO).
Lupo says a weak La Niña played a role in the devastating drought of 2012. That summer was marked by high temperatures and sparse rain. As is typical for La Niña 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 Niño and La Niña 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 Niño 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 Niña/La Niña and Missouri's corn and soybean yields.
"We're finding that when it's transitioning into El Niño years, the corn yields are higher," Donovan says. "Then when it's transitioning into La Niña, 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.
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