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Blame the ‘corn sweats’ for excessive perspiration

Duane Friend, Urbana, IL - As I write this article, corn has tasseled on about 80% of fields in central Illinois. Apologies to those with corn pollen allergies!

Corn, just like other plants, experiences evapotranspiration. Evapotranspiration (ET) happens when water is taken up by corn plants, and water vapor – the gas form of water – is released into the atmosphere from the leaves while evaporation occurs from the soil, also adding water vapor to the air. 

During the height of corn growth, a huge amount of water vapor is released into the atmosphere.

What is “corn sweat”?

This term relates to the high humidity created from the evapotranspiration from corn. At its peak, corn can add up to 4,000 gallons of water vapor to the atmosphere per acre per day.

For reference, there’s a little under 93 million acres of corn planted in the United States in 2021. This added moisture raises humidity levels, which has several effects on weather.

How does corn evapotranspiration affect weather?

One of the effects, as you might have guessed, is that the added moisture in the air makes it muggy outside. 

  • Increased heat index: More water vapor in the air decreases evaporation off our skin, which in turn can increase chances of heat exhaustion, etc.
  • Moderator of temperatureHigher humidity decreases the chances for extreme high actual temperatures, but the “feels like” temperatures may be quite high.

At night, there’s not as much of a dip in temperatureOpening the windows at night doesn’t work well because all you’re letting in is still warm, wet air.

Evapotranspiration in Corn vs. on the Prairie

Now you may be thinking, how does this evapotranspiration compare to natural vegetation, or in other words, prairie? 

Recent studies showed the amount of evapotranspiration between cornfields and prairie habitats are fairly similar in eastern areas of the Corn Belt, but corn may have much higher evapotranspiration in dryer areas such as the Great Plains.

The timing of peak evapotranspiration is also different. Prairie hits its evapotranspiration peak earlier in the season compared with corn. That may mean summer mugginess was not as great when prairie covered the landscape, but that is just speculation on my part.

Does the higher atmospheric moisture from corn during the summer increase chances for precipitation?

One study says yes. According to an article in Geophysical Research Letters, results of both regional climate model simulations and observational analyses suggest that much of the observed rainfall increase — as well as the decrease in temperature and increase in humidity — is attributable to agricultural intensification in the central United States.

What does it all mean?

To sum it up, corn affects our weather by:

  • Decreasing chances for extreme high actual temperatures during the day
  • Increasing the “feels like” temperatures
  • Increasing chances for higher nighttime temperatures
  • Increasing chances for more rain
  • Making the air feel more tropical

Some are good, some are uncomfortable. But those of us who have lived in the Midwest most or all of our lives expect this, don’t we? It makes late summer and early fall feel glorious!


Duane Friend is an energy and environmental stewardship educator with University of Illinois Extension, serving the organization in many roles since 1993. Duane provides information and educational programs about soil quality, weather and climate, energy conservation, and disaster preparedness. 

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