Published on July 24, 2025 at 8:30 p.m.
A heat dome is currently raging in the south of the United States. The Midwest is particularly affected, and the immense corn fields worsened the situation. Explanations.
Felt 53
An intense heat wave is currently sweeping a large part of the center and eastern United States. Raised by a heat dome, it leads to extreme temperatures that can exceed 38 ° C. But it is atmospheric humidity that makes this heat unbearable. And in the Midwest region, it is amplified by … the fields of corn. This strong humidity has increased the heat index (the American version of the humidx factor, or the feeling), up to 47 ° C. We even observed a 53 ° C heat index in Missouri. At this level, the air seems unbreakable.
An little known phenomenon
But what does corn come in there? The term “corn sweatshirt”, literally translated as “corn sweat”, designates the amount of water vapor emitted daily by the corn plants in summer. It is the result of evapotranspiration, combining the perspiration of the leaves (by stomates) and direct evaporation of wet soil. Currently, a square kilometer of corn plants releases up to 3 million liters of water per day. All plants produce water vapor, but for example, a square kilometer of corn produced 40 times more than the same surface of a forest of oaks.
Heavy heat
The emitted water greatly increases the dew point, giving air a tropical character. We observed dew points which exceeded 30 ° C at the start of the week in the Midwest. This level of humidity prevents body sweating from being effective, limiting the body’s ability to evacuate heat and increasing the risk of heat stroke, exhaustion or thermal shock, especially for vulnerable people and outdoor workers.
The aggravating role of the “heat dome”
This high pressure dome blocks the air masses, amplifies the solar effect and maintains a stagnant atmosphere. It channels the warm and humid air from the Gulf of Mexico and the Atlantic, adding an additional layer of humidity to that produced by corn. Result: persistent heat day and night, without real nightfield. This absence of night refreshment further increases thermal stress.
