WBRZ Weather

Impacts of the heat index

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Posted: Jun 17, 2014 10:34 AM by Meteorologist Robert Gauthreaux
Updated: Jun 17, 2014 10:34 AM
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As noted by the Southern Regional Climate Center at LSU last week on their Twitter feed, there were more heat fatalities last year than lightning and tornadoes combined. A total of 92 deaths were a direct result of the heat. Yesterday's article discussed the heat index, dew points and evaporative cooling.

One may recall the Midwestern heat wave in 1995 that was responsible for hundreds of fatalities, most notably in the Chicago area in July. An overconsumption of energy led to power failures and rolling blackouts. This only augmented the problem.

A key feature of this event was the development of very high dew point temperatures over the southern Great Lakes region and the Upper Mississippi River Basin. As stated yesterday, the heat index is dependent on the dew point temperature, and the combination of high temperatures and high dew point temperatures led to extremely high heat indices and the deaths of many citizens. The dew point is indicitave of how much moisture is actually in the air.

A few factors are thought to have played a key role in the high dew point values. One being evapotranspiration, which is a process within the hydrological cycle where water from the earth has the opportunity to be released into the atmosphere. Adjacent to the city of Chicago, is one of the greatest soybean and corn growing areas in the world; plants which are very effective in moving water from the ground to the lower atmosphere, thus affecting the dew point. The 1995 heat wave happened to coincide with the most active growth season for corn and soybeans. In modern times, agricultural practices have changed where planting densities are greater, as well as different cultivation techniques. This could potentially allow more plants to transpire into the atmosphere.

Another factor to consider, is that the Midwest saw a very wet spring that year. There was an abundance of moisture in the soil, deep into the ground near the root zone.

In the heat of the desert, there is no moisture. Whatever the temperature happens to be, that's what it feels like. Only in humid areas, does the heat index show that it feels hotter than it actually is.

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