Iowa Doesn’t Just Grow Corn… It Grows the Humidity

If you've stepped outside anywhere in Iowa or the Midwest lately and felt like you were walking through warm soup, welcome to the club. You're officially the latest victim of our annual, attack of the killer corn... no not tomatoes.

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Fair season is here across the state, and with it temperatures have been climbing into the upper 80s and 90s. However, the real heat driver might be growing just beyond your backyard. Welcome to Iowa's corn sweat tradition, where millions of acres of corn team up with summer heat to make it feel even steamier than a boiled and buttered cob.

I've had a front-row seat to this show for some 41 years. From my earlier years growing up on an Iowa farm, I've really felt it now more than ever. It's been brutal for heat while coaching youth soccer this summer. Nearly every practice and game has meant adding extra water breaks for players, coaches, and referees alike. On some of the hottest days, teams have even decided it simply wasn't worth the risk and canceled matches altogether. When kids are asking for another water break after just a few minutes on the field, you know it's more than just "another hot Iowa day."

After one of the muggiest stretches of the summer, much of Iowa has been dealing with temperatures in the 90s while dew points climbed into the low 80s in some locations. That's about as uncomfortable as it gets, making it feel like you're stepping into a sauna the moment you walk outside. So, why exactly am I sticking to myself?

Well as corn grows during the peak of summer, it pulls water from the soil through its roots before releasing it through tiny pores in its leaves in a process called transpiration. It's how the plant naturally cools itself, much like humans sweat to avoid overheating. Now imagine millions of corn plants all doing that at the same time.

During peak growing season, a single corn plant can release up to four cups of water into the atmosphere every day. Multiply that across Iowa's nearly 13 million acres of corn, and the amount of moisture entering the air is staggering. One acre of mature corn can release anywhere from 3,000 to 4,000 gallons of water every day. Talk about your tropical climate! That's one reason Iowa often feels "rain forest" muggy in late July and into August.

Credit: NOAA | Apparent Temp for July 29 at 4pm.

Meteorologists measure that stickiness using something called a dew point. Once dew points climb above 70 degrees, the air starts feeling tropical. Above 75 degrees, most people describe it as oppressive. During this latest heat wave, parts of Iowa saw dew points in the low 80s, creating dangerous heat index values well over 100 degrees and making even simple outdoor activities exhausting.

Credit: NOAA | Corresponding Dew Point for July 29 at 4pm

By the way, that extra humidity also makes it harder for your body to cool itself. Sweat doesn't evaporate as easily, so instead of cooling you down, it just leaves you feeling sticky, wet, and hot. That's why walking to the mailbox can feel like a workout, mowing the lawn feels twice as hard, and youth sports need extra breaks to keep everyone safe.

As much as we like to complain about corn sweat, those endless green fields are doing important work. Corn absorbs carbon dioxide, releases oxygen through photosynthesis, feeds livestock, helps produce ethanol, and provides ingredients found in thousands of everyday products. The same transpiration that makes Iowa feel like a steam room also helps cool the plants so they can continue growing through the hottest days of summer. During a growing season, one acre of Iowa field corn produces about 12.5 tons of oxygen.

So, the next time your sunglasses fog up, you feel like you're swimming through air, and your T-shirt sticks to your back by 9 AM, don't blame the weather. Blame the millions of acres of corn. Just don't do it too loud, because around here, Iowa's corn doesn't just make the forecast, it also cleans the air and feeds world!