How ‘corn sweat' is driving up humidity across the US - and yes, even New England

Boston Globe

a day ago

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This week's heat dome, which has blanketed the eastern half of the US and the Midwest with intensely hot temperatures by trapping warm air near the surface, was compounded by the presence of corn sweat in the atmosphere.
The rotation of this high-pressure system has been driving a southwesterly flow toward New England, picking up that added moisture or corn sweat from the Midwest, and with the help of the west-to-east flow of the jet stream, has been funneling more humidity our way. That moisture-laden air has been pushing up heat index values, making it feel a lot hotter.
Take a look at the extra water vapor moving into New England through Friday, amplified by the additional corn sweat from the Corn Belt.
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The progression of additional water vapor pushing over New England, boosted by excessive "corn sweat" from the Midwest.
Pivotal Weather
Friday's temperatures in New England are
Andy Vanloocke, associate professor of agriculture and meteorology at Iowa State University, says the corn plants act like straws between the soil, water, and the atmosphere.
'The water that's evaporating over Iowa right now, a significant portion of it, depending on the weather patterns, 70 to 80 percent will fall again before it exits the Mississippi River Basin,' Vanloocke says. 'But some of it will make its way all the way to Boston before eventually falling out. It may even cycle a few times between the land and the atmosphere on its way over there.
'If you're having a hard time believing that, just think about the amount of smoke you get from a wildfire blowing through thousands of miles,' he says.
Corn is the most abundantly produced crop in the United States, and the plant releases water vapor into the atmosphere at one of the fastest rates among all plants. A single acre of corn can add about 4,000 gallons of water per day into the atmosphere, amplifying the moisture content and increasing dew point and humidity, according to the U.S. Geological Survey.
And, basically, the higher the temperature is, the more moisture the corn will draw from the ground and release, or transpire, into the atmosphere.
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'When you have a warm atmosphere with a lot of demand for that water, that leaf area is going to generate a lot of water vapor for the atmosphere,' Vanloocke says.
Many experts believe this corn sweat effect has expanded from a rather local event to a more expansive phenomenon due to climate change.
Most corn production is located across the Midwest, Plains, and Ohio Valley.
USDA
Besides corn, Vanloocke said, soybeans are just as prevalent and equally efficient at evapotranspiration.
'We should call it soy sweat as much as we call it corn sweat,' he said. 'There are about as many corn acres as soybean acres out here in the Corn Belt… and soybean uses just about as much water on a day-to-day basis as corn does.'
Ken Mahan can be reached at