Does ‘wheat sweat’ add humidity to region’s weather?

Ripened wheat in the Inland Northwest, taken in late July. (Photo by Henry Moore)

By Nic Loyd, WSU meteorologist, and Linda Weiford, WSU News

weathercatch(2) (2)SPOKANE, Wash. – “Corn sweat” made big news in late July as the Midwest baked and wilted in heat and humidity. Television reporters standing waist-deep among corn stalks explained how millions of crop acres across the nation’s Corn Belt were contributing to a stretch of miserable weather.

Corn sweat – technically known as evapotranspiration – was partly to blame, they said.

The phenomenon occurs when moisture is drawn into plants from the soil and ultimately evaporates into the air. Though the extra moisture doesn’t make the weather hotter, it can make it more humid.

And if you’ve ever spent time in a heat wave accompanied by high humidity, then you understand how a temperature of 90 degrees feels much higher. Called the heat index, it’s what our bodies feel when heat and humidity are combined.

We don’t have loads of corn crops in this region, but we do have an abundance of wheat. Does this mean it profusely “sweats” when temperatures soar, impacting our weather?

Wheat undergoes evapotranspiration as well, but not to the extent that corn does in the nation’s midsection. Moisture flowing off the Gulf of Mexico drives a lot of humidity into that region, fueling the evapotranspiration process. Because our climate is considerably drier, there’s less moisture in the ground to be siphoned into crops and released into the air.

Also, all those ears of corn mature at roughly the same time, acting as one massive moisture wick from Minnesota to Missouri. Conversely, the two main wheat varieties planted in this area reach peak maturity at different times. And finally, densely planted Midwest corn covers far more acres of land than wheat does in the Inland Northwest.

So while corn-crop evapotranspiration pumps plenty of moisture into the air during the dog days of summer, there’s not so much among our amber waves of grain.

We sometimes experience wind storms, drought and wildfires, but when it comes to high humidity, it’s no sweat.


Weathercatch is a bimonthly column that appears in The Spokesman Review. Nic Loyd is a meteorologist with WSU’s AgWeatherNet. Linda Weiford is a WSU news writer and weather geek. Contact: