Janice R. Andrews
This week, the Midwest is experiencing a very hot spell that has caused excessive heat warnings, heat alerts, and even school closures in Wisconsin and nearby states. The oppressive heat is mostly caused by an upper ridge, a weather trend with high air pressure that brings hot, muggy air from the southern Gulf states into the area.
The intense heat has been made worse, though, by something less well known: “corn sweat.” Even though the word “corn sweat” sounds silly, it is a real and important process that can make the Midwest much hotter and more humid, especially in states like Wisconsin, Illinois, Iowa, and Minnesota that grow a lot of corn.
How to Understand Corn Sweat: The Science Behind the Word
Even though they are called maize plants, they don’t really sweat. The process of evapotranspiration, in which water leaves the leaves of plants (including corn) and is released into the air, is called “corn sweat.” This natural process is how plants “breathe” and control how much water they have.
When a plant’s roots pull water from the dirt, evapotranspiration starts. This water moves through the plant’s cells and helps with many physiological and biological processes. In the end, the water is released as vapour through stomata, which are tiny holes in the leaves. The humidity level goes up because this water vapour makes the air more wet by adding to its moisture content.
The U.S. Geological Survey says that during the growing season, an acre of corn can send about 3,000 to 4,000 gallons of water into the air every day. Since the Midwest has a lot of cornfields, this process can have a big effect over time, making the air much more humid.
What Corn Sweat Does to Heat and Humidity
There is a lot of evidence that dampness and felt temperature are linked. People feel hotter when there is more humidity in the air. In this case, the National Oceanic and Atmospheric Administration (NOAA) says that it feels like 91 degrees when the air temperature is 90 degrees Fahrenheit and the relative humidity is 40%. If the humidity goes up to 80%, though, the temperature seems to go through the roof, reaching 113 degrees.
This is where maize sweat comes in. In places like the Midwest where corn is grown in large amounts, the crops’ water loss can raise the dew point (a measure of how much water is in the air) by several degrees. So, the heat indices, which are temperatures that take humidity into account, can rise to dangerously high levels, making the already unbearable heat wave even worse.
Which states are the worst hit by maize sweat?
The states with a lot of cornfields are the ones most affected by corn sweat. Iowa, which grows more corn than any other state, for example, lets out up to 56 billion gallons of water into the air every day while the crops are growing. This huge amount of water vapour can raise the dew point by 5 to 10 degrees, which has a big effect on the weather in the area.
In 2023, these were the states in the U.S. that grew the most maize:
- Iowa: 2.5 billion bushels
- 2.3 billion bushels in Illinois
- 1.7 billion bushels in Nebraska
- 1.5 billion bushels in Minnesota
- Indiana: 1.1 billion bushels
- It was 854.2 million bushels in South Dakota.
- Ohio: 673.2 million bushels
- There were 612.9 million bushels in Kansas.
- There were 561.5 million bushels in Missouri.
- 552 600 000 bushels in Wisconsin
When there are heat waves, these states are especially at risk for maize sweat because the mix of high temperatures and high humidity can make heat indices dangerously high.
A Sign That Crops Are Healthy, But a Challenge for People
Even though maize sweat can make the Midwest’s summer heat waves even worse, it’s also a sign that crops are healthy and growing well. When plants are stressed, like during a drought, they close their stomata to save water. This lowers evapotranspiration and could stop growth. Because of this, maize sweat means that the plants are getting enough water and are healthy.
To sum up, maize sweat is a big part of the Midwest’s summer heat that is often forgotten. Since millions of acres of corn release water into the air, the humidity rise can make the already uncomfortable heat dangerous for people living in the area. If you live in or are travelling through the Midwest during the growing season, you need to understand this occurrence.
