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Corn Sweat: How crops lead to a local increase in humidity

Published: Jul. 27, 2021 at 12:03 PM CDT
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OMAHA, Neb. (WOWT) - If you’ve lived in the Heartland long enough, you’ve likely heard the phrase “corn sweat”.

During the heat of the summer, particularly July into early August, our dew points peak. The AMS glossary definition of dew point is: “The temperature to which a given air parcel must be cooled at constant pressure and constant water vapor content in order for saturation to occur”.

Meteorologists often use dew points - rather than relative humidity - as our preferred measure of how humid the air is. When dew points rise into the 60s during the summer, it starts to feel muggy. 70s are steamy, and 80s are downright miserable.

Dew point scale
Dew point scale(WOWT)

From a meteorological perspective, the mid to late-summer peak of humidity makes sense. Warmer air can hold more moisture, and dew points can *never* be higher than the air temperature. Meaning, you need warmer temperatures for higher dew points.

Dew points can differ – sometimes greatly – on our weather maps from city to city on a given summer day. Acres of corn contribute to localized rises in humidity. Humidity is often higher in rural areas, where more bushels of corn are grown. In fact, Omaha frequently has a lower dew point than the surrounding areas due to lack of corn grown in and around the city.

Corn production by county
Corn production by county(USDA)

So what is “corn sweat” anyway?

In humans, sweat is a body’s natural air conditioner. When our body temperature rises, sweat is released from the skin through evaporation. This draws heat away from the body in a process called “evaporative cooling”.

Plants have their own cooling process. After drawing water from the soil, plants release moisture from their leaves through transpiration. According to NWS Omaha, an acre of corn can “sweat” up to 4,000 gallons of water in a day! This released moisture from corn can cause localized increases in humidity, leading to higher heat indices around and downwind of corn fields.

Corn can sweat up to 4,000 gallons a day!
Corn can sweat up to 4,000 gallons a day!(WOWT)

Dew points in the 80s are normally reserved for the Gulf Coast, but this extreme humidity is not out of the question near a corn field in the Heartland during the heat of the summer.

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