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As the Midwest braces for punishing heat this week, a natural but often overlooked phenomenon is making things even worse: “corn sweat.”
Scientifically known as evapotranspiration, this process involves plants — especially corn — releasing water vapor into the atmosphere. According to crop intelligence firm Taranis, the cumulative effect of this vapor significantly increases humidity, making already hot summer days feel even more oppressive.
The Midwest and Plains regions, home to millions of acres of corn and soybeans, are particularly affected. During peak growing season, each acre of corn releases an estimated 3,000 to 4,000 gallons of water per day into the air. In Iowa alone, corn contributes a staggering 49 to 56 billion gallons of water daily, which can raise the dew point — a key humidity indicator — by 5 to 10 degrees on hot days, according to the National Weather Service.
Illinois, with about 12 million acres of corn, releases 48 billion gallons of water into the atmosphere each day — enough to fill over 73,000 Olympic-size swimming pools.
However, experts emphasize that weather patterns remain the primary driver of high humidity and heat. Iowa State Climatologist Justin Glisan noted that while corn transpiration contributes to local moisture, it is secondary to broader weather systems. Moisture carried from the Gulf of Mexico or the Pacific Ocean, through southerly and westerly winds, plays a far greater role in increasing humidity across entire regions.
This week, a large heat dome over the Midwest will bring extreme conditions. The heat index — which measures how hot it feels factoring in humidity — is expected to reach 115 degrees Fahrenheit in Illinois by Wednesday and Thursday, July 23–24. Parts of Texas, Arkansas, and Louisiana are also forecast to see temperatures near or above 100 degrees.
Despite its discomfort, evapotranspiration is a positive sign for agriculture. Taranis reports that the process reflects healthy, growing crops and is vital for helping plants reach maturity. Corn sweat may make the air feel heavier, but it signals a productive season for farmers.
