In the Midwest and Northern Plains, corn and soybean crops draw moisture from the soil through their roots into their leaves, stems and fruits. Water evaporates into the surrounding air through their leaves, joining forces with neighboring water molecules to moisten the air.
That extra moisture makes the heat wave centered in the middle of the Lower 48 states even more oppressive.
Densely planted on millions of acres, corn can bring corn levels of moisture in mid-summer. An acre of corn can release 4,000 gallons of water per day, enough to fill a home swimming pool in less than a week.
The added moisture from the corn causes higher heat indices – a measure of how hot it feels taking moisture into account. It can turn an oppressive day into a dangerous one. The effects are strongest in the heart of planted fields, but a person does not need to be standing in a field to feel the heat. The moisture follows the winds, mixing around to cover the area.
Temperatures on Tuesday rose from 95 to 105 degrees across the Plains and Midwest, but high humidity pushed heat indices into the 100s to 110s from Texas to southern Minnesota.
On Wednesday, heat indices are forecast to soar again across much of the southern Plains, extending as far northeast as southern Michigan.
While warmer conditions favor higher rates of evapotranspiration, the process peaks when the corn reaches the “tassel” stage, or when it reaches its maximum height – with a crown of fine spikes – and begins to sprout. The tassel generally appears around mid-July to August, about 80 to 90 days after planting. Humidity levels may increase over a week or two once the plant reaches the tassel stage.
Moisture from corn evapotranspiration can not only make it unbearably cloudy during the day, but can also slow down cooling at night, leaving little respite from the heat. Lows Wednesday from Texas to Illinois fell only to the 75s to 80s, about 5 to 15 degrees above normal. The low temperature in Des Moines was just 82, Its warmest minimum temperature since July 1936.
When the ingredients are in place for showers and storms, added juice can make them more intense. That could happen in parts of the Midwest on Wednesday, the National Weather Service said increased risk of severe storms.
However, corn isn't the only culprit in summer humidity. Soy also contributes significant moisture through evapotranspiration. In other words, soy also sweats. Moisture also evaporates from bodies of water and even from wet soils in areas with recent rains. Not to mention much of the moisture that reaches the corn belt during the summer comes from the Gulf of Mexico and sometimes even the Pacific Ocean.
In other words, corn does not act alone. But it might just be one more thing pushing the summer heat from miserable to miserable.
If it's mud in the middle of America in the middle of summer, go ahead and blame it on the corn. Just don't forget its friends: soybeans, soil and waterways, to name a few.
Barb Mayes Boustead is a meteorologist and climatologist living in the heart of the Great Plains. Her interests include the overlap between weather and climate, especially in extreme weather, as well as historical weather phenomena such as the one at the heart of Laura Ingalls Wilder's work.The long winter.” She is a thesis awardee from the American Association of State Climatologists and past president of the Laura Ingalls Wilder Heritage and Research Association.
Jason Samenow contributed to this report.
