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Seasonal trends favor rough Corn Belt weather in '08

Agriculture.com Staff 03/17/2008 @ 2:59pm

Watch the southeastern U.S. for signs of weather that could harm the '08 corn and soybean crops in the Corn Belt this summer. That's the message from Iowa State University ag meteorologist Elwynn Taylor, who says the Midwest may be due for drought if models to date hold true.

The last major crop-limiting drought hit the Corn Belt in 1988. While he says it wasn't enough to totally wipe out that year's crops, Taylor says it reduced yields by an average of 30% through the central and eastern Corn Belt. With this year marking the 20th anniversary of that weather event, the region's already past due for overall drought conditions.

"Serious drought tends to follow a 19-year cycle, and the next four years fall into the higher risk portion of that cycle," Taylor says. "The majority of seasonal weather indicators imply increased crop production risk for the 2008 crop season."

Several indicators play into Taylor's assessment of risk for drought this year. First, he says when dry conditions in the southeastern U.S., like what's occurred in that region in the last year, that often leads to an extended drier period in the Corn Belt. Specifically, a drought in South Carolina is the most likely precursor to similar conditions further northeast.

"Some level of drought in South Carolina precedes the initiation of widespread Corn Belt drought. Greater than 90% of all major Corn Belt droughts are preceded by drought in South Carolina," Taylor says. "The risk of serious drought in Ohio is greater than 60% if June drought occurs in South Carolina, and there is a 36% chance of Corn Belt-wide drought within 15 months."

Meanwhile in the southwestern U.S., data is less conclusive, but still comprises a trend that could mean drought in the Midwest this year. A 60-year cycle -- as proven by the long-term study of tree rings from Arizona to Virginia -- shows that a drier-than-normal year in the desert Southwest often precedes below-normal moisture levels in the Midwest. This longer-term trend could mean a series of drought years, though these numbers are less consistent, Taylor says.

"Drought originating in the Southwest is not known to sweep the Midwest; however, a series of dry years in the Southwest may precede below normal moisture years developing in the eastern half of the U.S. During the past 100 years the wet/dry relationship is discernible in weather records," he says. "The similar pattern seems to lag somewhat, moving from west to east. The 'dry' trend in Arizona may be an indication of a 30-year trend toward more arid conditions there. The trend appears to have initiated about 1980.

"It is possible that much of the Midwest reached the 'peak' of moisture in the mid-90s and may experience diminishing annual moisture over the next two decades."

It's been associated with a lot of anomalous weather around the globe in the last few months, but will La Niña continue to affect U.S. crop weather through this summer? Chances are good, Taylor says, that La Niña will fizzle before the heat of this summer's growing season comes on.

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