Heavy Rain and runoff

MT. VERNON, Ill. — Climate change is real and it’s here. How farmers will respond to it is another question.

Without addressing the cause, WSIL-TV meteorologist Jim Rasor said he believes changing weather is the new normal for the planet, though at differing levels in local geographies.

“The trend line is up. Global temperature is rising,” he said at a conference here. “I’m not talking about whether it’s manmade or natural. It’s there.”

Rasor is more concerned about practical applications of changing weather patterns.

“I don’t care that it’s global. I want to know what it’s doing right here in southern Illinois,” he said. “I want to know how it affects farmers.”

His work tracking weather for 30 years has uncovered information that may be of use for farmers in the region. For one thing, average first and last frost dates have changed.

The average first frost — defined as any temperature below 33 degrees — has gradually moved. When Rasor first began tracking dates 30 years ago, the average first frost occurred on Oct. 8. It is now Oct. 26.

“That’s a pretty significant move,” he said. Likewise, the average last frost has moved from April 15 to April 6.

But his region is bucking the global trend in rising temperatures.

“What we found, and well defined, is that our warming locally is on the low side,” Rasor said. “Our low daily temperatures are going up. But when we look generally at what’s going on, the overnight lows are getting warmer.

“There’s a trend line there that is relatively flat. So our global warming doesn’t mean afternoon temperatures are skyrocketing. They’re holding about the same. It’s our overnight lows that have gone up.”

Conversely, average January and February temperatures are trending lower.

“That’s not going to happen every year, but it’s now the rule rather than exception,” he said.

And while precipitation is also on the upswing, the numbers don’t tell the whole story. Rasor is in the process of forming a trendline chart of usable rainfall, something that would be more useful to farmers.

“We’re getting more rain in fewer days. When we finished last year, my gauge was 10 inches wetter than normal,” he said. “There were way too many events in that where more than half of the rain in a 24-hour period ended up in my ditch, or a in a pond.

“I’m working on coming up with a way to throw away what we think is runoff and come up with numbers a little closer. At the end of last year, it might be that the rainfall number was 10 inches wetter than normal, but it could be 2 inches drier than normal.

“Just telling you that it’s 7 inches wetter than normal when we know 5 inches ran off in one night is useless information. I think it’s an issue.”

He doesn’t put much stock in long-term forecasts, taking a jab at national forecasts that put portions of the country at “EC” for temperature or precipitation. The letters stand for “equal chance,” which means the forecast is “worthless.”

“There is not an extended weather outlook product out there that is worth a damn, including mine,” Rasor said.

He recommends that farmers find a local forecaster they have faith in.

“Make friends with, or at least identify with, a local source of information you trust, that you would bet your farm on,” he said. “A national source is never going to be as good.”

Nat Williams is Southern Illinois field editor, writing for Illinois Farmer Today, Iowa Farmer Today and Missouri Farmer Today.