La Niña and Corn Yield

El Niño is waning quickly this spring, and La Niña is forecast to take its place by the fall. The 2015-16 El Niño had quite an impact in South Dakota, as we had above average winter temperatures. Consistent with many of the climate outlooks, Northern South Dakota was drier than average and Southeastern South Dakota was much wetter than average. Now that we are in the transition, we have seen much wetter conditions across the state.

When climatologists look to clues for seasonal climate forecasts, we consider sea surface temperatures in the Pacific Ocean near the equator. This is the measurement that signals if El Niño or La Niña conditions are developing, in place, or waning. Currently, the Eastern equatorial Pacific is cooling and more than half of the long-range climate models are forecasting a swing towards continued cooling beyond the temperature threshold that is required for an “official” La Niña to be declared.

Growing Season Outlook
With La Niña more than 50 percent likely to develop by harvest season, what does that mean for our growing season in South Dakota? For the answer, we look to the Climate Patterns Viewer, a tool developed by the Useful 2 Usable project in the Decision Dashboard. With this tool, it is possible to look at all La Niña years in the past 30-year period. Then we chose to view the corn yield during those years, expressed as a departure from average.

This map shows mixed results in the state. The primary corn growing areas in far Eastern South Dakota tend to have slightly lower yields during La Niña years, compared to the long-term average, with a difference of less than 5 bushels/acre on average. In the regions just east of the Missouri River in Northern and Central South Dakota, corn yields have historically been just above the long term average by less than five bushels/acre during La Niña years. So overall, corn yields can be mixed during La Niña years.

Looking further east across the Corn Belt, some areas of Minnesota, Wisconsin and Iowa have historically had lower yields in La Niña years. In general, it appears that La Niña has not been a boon to corn yield in the past.

Source: Laura Edwards, South Dakota State University Extension

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