Tired of humidity? Blame corn sweat for the muggy air
Corn can make a warm summer day feel even more humid. Here’s how
Nothing makes a hot day feel worse than a heaping dollop of humidity. Southerly winds surging across the border can lend a tropical feel to the air over Canadian soils, but something growing in those soils can actually generate humidity and make it feel more brutal.
Vegetation is a major contributor to humidity on a sultry day. There are few crops that give off more moisture than corn.
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Humidity is brutal because it affects your body’s ability to sweat. We cool off when we sweat as the water evaporating into the air draws heat away from our skin.
When there’s excessive humidity in the air, though, sweat can’t evaporate as easily and our bodies struggle to wick away the excess heat to cool us down.
It turns out that corn sweats, too—but not quite for the same reason.
Plants need a significant amount of water to grow. This water doesn’t stay in the plant for long. Grass, flowers, crops, trees, and even your houseplants all lose water through their leaves as part of a process known as evapotranspiration.
The United States Geological Survey highlights the extent to which plants give off water vapour every day. A single big oak tree can give off 151,000 litres of water into the atmosphere in an average year. Scientists estimate that the Amazon rainforest recycles nearly 80 percent of its prolific rains back into the atmosphere every year.
But get this—one acre (0.4 hectares) of corn can give off up to 15,000 litres of water vapour every day, the USGS says. That’s a tremendous amount of "corn sweat" pouring into the air around our communities on a daily basis during the growing season.
A map of corn production across Eastern Canada. (USDA)
Nearly 90 percent of all the corn raised in Canada grows across southern Ontario and southern Quebec, according to Statistics Canada and the U.S. Department of Agriculture. Most of that corn originates from southwestern Ontario, and for good reason—it's routinely one of the hottest parts of the country.
This vast output of corn can aid southerly winds in boosting humidex values into the 40s on the hottest summer days, making it feel absolutely brutal outside without proper hydration and protection.
A particularly brutal example of this process played out in August 2024 across the U.S. Midwest, where this corn sweat helped push dew point values in excess 25°C—a level beyond what you’d typically see in the tropics. The humidex value at Chicago’s O’Hare Airport rose into the upper 40s on the hottest afternoon of that heat wave.
Header image courtesy of Unsplash.
