How does corn sweat affect humidity and heat index values?
COLUMBUS, Ohio (WCMH) -- Cruising past a cornfield, you may not realize just how much moisture enters our atmosphere surrounding an area of farmland. Ohio farmers planted 3.25 million acres of corn this spring, according to the U.S. Department of Agriculture (USDA), part of the 95.2 million acres in total across the nation.
A single acre of corn can release 3,000-4,000 gallons of water into the atmosphere in a single day during the peak growing season in response to warmer weather, which adds up to between 11 and 14 billion gallons statewide.
During the process of photosynthesis, which involves a reaction with sunlight, carbon dioxide and water, sugars (food) are produced and oxygen is released. The water is drawn upward from the soil, and emitted by the leaves from the stomata, which open up with light.
Corn sweat yields a 10% increase in humidity through the process of evapotranspiration, and coupled with ambient moisture is more than sufficient to drive up the heat index value (temperature and humidity) to dangerous levels in excess of 100 degrees on hot, sunny days. Transpiration reaches a maximum just before corn enters its reproductive stage (tasseling and pollination).
Recent weeks have witnessed more than 2,000 reports of flooding in the U.S., exacerbated by slow-moving storm systems. Above-normal water temperatures in the western Atlantic and Gulf have factored into record rainfalls and flash flooding, drawn northward by a stagnant area of high pressure in the Southeastern states.
Atmospheric moisture supplemented by corn sweat over the Corn Belt has fueled thunderstorm complexes that often bring rainfalls of 1-3 inches in an hour.
Another Hot July
July 2025 averaged 2.9 degrees above normal in Columbus (78.3 degrees), tied for the 16th warmest since 1878. However, the average minimum temperature (69.6 degrees) ranked as the fourth warmest, an indication of high humidity keeping nighttime temperatures from cooling off, compared to a more normal summer pattern.
Temperatures measured at John Glenn Columbus International Airport averaged above normal on 26 days in July. The warmest July occurred in 2012 (80.5 degrees), when the mean minimum for the month was 69.9 degrees (tied with July 2011 for second, after July 1878).