THE CORN IS SWEATING...

Here in the Midwest it seems as though it's getting harder and harder to regulate our weather. While it's true averages are comprised of extremes, we seem to lean more towards the extremes in recent years. Like it or not our climate is evolving to warmer temperatures, (especially sea surface temperatures) which is leading to increased water vapor. It's a physical fact that increased CO2 (carbon dioxide) warms the planet. It's also proven that warmer air holds more water vapor. The extra water vapor holds more heat. This is turn makes the air even warmer.

What I've noticed is that with the extra water vapor we see less temperature extremes. It's not as hot during the day but it's warmer during the night. Take warmth for example. The last time Dubuque, Iowa officially reached a temperature of 100 degrees or higher was July 25, 2012 (16 years ago). On that day, the city recorded a high of 101 degrees. Taking it a step further, since 1941, the 100-degree threshold has only been met five times in the city. In today's climate, it's rare to see a day reach as warm as 95 locally.

Why is that? You can blame it on the higher amount of moisture in the air, which is directly measured by the dew points. The great majority of 100 degree days in our past (pre-1985) occured when dew points were in the 50s and 60s. Now, it's rare not to have a summer when we don't see several days with the dew point in the 80s. During the massive July 1995 heatwave, Cedar Rapids measured a record dew point of 86 degrees July 13th. That dew point and a 100°F air temperature created a historic heat index of 131°F. The New England Journal of Medicine reports as many as 700 people may have died from heat related causes, mainly elderly shut-ins without air conditioning.

The point I'm making is that ambient temperatures may not reach more than the mid-90s in today's summers. However, we may see several weeks of dew points that reach 75-83. Those easily produce heat index readings (how it feels with all the humidity) of 100-110+, with highs only 94-97. In the old days, with drier air and lower dew points, a high of 100 felt like 100. Summer's now, thanks to increased water vapor are cooler on the thermometer but often worse to endure due to the extreme humidity and sweltering heat index values that result.

This July alone, 11 days in the Quad Cities have had dew points of 70 or above. That 73 percent rate seems to be about on par for what today's averages would indicate, and part of the reason recently is corn pollination.

AS IF WE NEED MORE WATER VAPOR

Here In Iowa and Illinois, we love our corn. But when it's tassling like it is now, you can blame the maize for contributing to your discomfort during this week’s heat wave. Sure, corn is easy to "pick" on, but it really does increase the humidity, a key factor in heat index readings around 100 this week. With corn fully grown and engaged in pollination, this is prime time for its contribution to high humidity.

Any large, deep-rooted plant puts moisture into the air through evapotranspiration — a process by which moisture in plant leaves evaporates into the air. Not surprisingly, corn, which covers about 36 percent of the state, is Iowa’s predominant large, deep-rooted plant.

When it’s fully grown and pollinating, as it is now, corn uses as much as 0.45 inches of water on a hot day. Some of that moisture helps the plant fill kernels, which are largely water at this stage of development, but “a good amount gets transpired.

 Because corn plants actively draw water from the soil, more water vapor escapes a cornfield than would evaporate from a lake of the same size. . During the peak summer growing season, a single acre of corn can release 3,000 to 4,000 gallons of water into the atmosphere every day. That can increase the dew point by as much as 10 degrees. No wonder it's humid!

More important to us as humans, is the fact water vapor emitted by corn plants can increase the dew point, the standard measure of moisture in the air. The dew point is the temperature at which the air is saturated with moisture, (the level where dew forms). That reading is used in combination with the actual temperature to calculate the heat index. The heat index calculates how hot the air actually feels to the human body when air temperature and relative humidity are combined.

Anyway you slice it, it's corn sweating season. And when the corn sweats, we pay. Hope you enjoyed this corny post. Roll weather...TS.