DES MOINES, IOWA — The summer heat is peaking here in Iowa as temperatures are expected to reach the mid 90s at many points this week and next. But did you know that the corn can make it feel hotter?

Just like humans, corn needs water to survive. When humans exercise or work outdoors in the heat, we transpire or sweat. Mature corn does the same thing!

FILE – In this July 11, 2018, file photo, a field of corn grows in front of an old windmill in Pacific Junction, Iowa. (AP Photo/Nati Harnik, File)

What are transpiration and evapotranspiration?

Water that the corn uses to grow is emitted back into the atmosphere. This process is known as transpiration. Unlike humans, corn doesn’t have a towel to absorb the water (or sweat) it produces. So instead the water evaporates into the atmosphere. This process is called evapotranspiration.

With millions of acres of corn maturing across the state of Iowa, the amount of water that evaporates into the atmosphere each day is an estimated 49-56 billion gallons. That’s enough to fill nearly 2 million (20x40ft) swimming pools.

More moisture=higher heat index

In a graphic posted by the National Weather Service in Des Moines, the extra moisture added to the atmosphere via corn can add 5-10° to the dew point temperature on a summer day. Higher dew point temperatures make the normal air temperature feel hotter.

Graphic courtesy of NWS Des Moines

The heat index tells us how hot it actually feels outside. The measurement of this index is based on temperature and relative humidity. For example, if the temperature is 95°F and the relative humidity is 45% (dew point of 70°F) the heat index would be 102°F. On the other side, extremely low humidity can cause temperatures to feel cooler. For example, if the temperature is 100° and the relative humidity is 15% (dew point of 40°F) the heat index would be 96°.

You can calculate the heat index using this graph from NOAA and the National Weather Service.

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