Is ‘corn sweat’ really to blame for Kansas City’s extra humid summer? Not exactly

This summer has been a scorcher, and sky-high temperatures have felt even worse due to the near-constant humidity in the air. This muggy weather has caused days in the 90s to feel like over 100 degrees during the past months—and summer still has more than a month to go.

But why is this summer more humid than last year, and what causes the humidity that makes walking outside a sticky nightmare?

Some news outlets, including the Washington Post, have blamed a phenomenon called evapotranspiration, or “corn sweat,” for the recent trend. This term refers to the evaporation of moisture from plant leaves into the air.

We spoke with a Missouri climatologist and a Kansas City meteorologist with the National Weather Service to see how much this phenomenon of “corn sweat” is really to blame.

Why has this summer been so humid?

Kansas City meteorologist Al Pietrycha told The Star that there are several factors at play—and while so-called “corn sweat” contributes to the humidity, it isn’t the main culprit.

“When we’re talking about humidity that you and I feel down here at the surface, a lot of that actually comes up out of the Gulf of Mexico,” he said. “That’s actually the biggest contributor to why it’s so sticky and hot… Now you throw in crops like corn, [and] that’s going to boost it a little higher.”

Pietrycha noted that “corn sweat” does contribute to muggy conditions in the metro, but that its impact isn’t as strong in Kansas City’s urban core as it is in more rural areas.

This summer’s humidity has also been caused by a zone of high air pressure in the Midwest that has stagnated throughout the hottest months. Pietrycha said that this “dome” has trapped the area’s humidity and high temperatures in place over the past 45 to 60 days.

Why does corn “sweat”?

While many crops experience evapotranspiration to some degree, corn is unique in the volume of water that can evaporate off it. This is due to the large surface area of its leaves and the amount of water it uses to grow. More moisture in the soil also leads to more of this “sweat.”

Pietrycha also added that the stage of a corn plant’s growth cycle can impact how much humidity it produces. Corn generally “sweats” during the tassel phase of its growth, which often falls in mid to late July. When it matures further and starts to brown, it no longer releases as much evaporation.

When will the weather cool down?

Humidity haters have something to look forward to this week: a Tuesday rainstorm is expected to bring cooler air into the Kansas City area for the rest of this week. Pietrycha said that while the season’s heat may not be over yet, the coming days should offer lower temperatures and humidity levels.

“I wouldn’t say we’re out of this yet. We can certainly have the high pressure build back in,” he said. “But we’re getting a break here this week for sure.”

Do you have more questions about weather patterns in and around Kansas City? Ask the Service Journalism team at kcq@kcstar.com.