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Wet Bulb Temperature

I read an interesting article this week about Wet Bulb Temperatures.  According to the CBC article, a wet-bulb temperature is a theoretical measurement that combines temperature and humidity. As we all know, hot dry days are different from hot humid days.  Essentially, the wet bulb temperature is a measurement at which water stops evaporating from a wet thermometer bulb. This is important to us because it’s the evaporation of sweat on our skin that cools us in the heat. In this case the bulb represents our skin. If the heat of this summer, especially on the western side of the country,  is an indication of what our future looks like, this measurement will be critical to our health.

Thermoregulation is the term used to describe the various processes the body uses to maintain its internal temperature. For the average person, a healthy internal temperature falls between 37˚C (98˚F) and 37.8˚C (100˚F). The body has some flexibility with temperature but the extremes (too hot or too cold) are dangerous. Thermoregulation is controlled by the hypothalamus section of the brain. In response to an internal temperature change the hypothalamus sends signals to the muscles, organs, glands and nervous system that in turn all work together to get the body’s temperature to a normal range. The body has two cooling methods:

  • Sweating: The sweat glands release sweat. The evaporation cools the skin and that helps to lower the internal body temperature
  • Vasodilation: The body vessels under the skin dilate and this increases blood flow to the skin where it is cooler and away from the warmth of the inner body releasing heat through radiation.

So far this summer, Canada has seen temperatures in excess of  40˚C. That number does not take into consideration the humidity. The humidex (humidity index) is used by meteorologists (apparently only in Canada) to describe how hot the weather feels to the average person. That doesn’t seem very accurate. Given that we’re now seeing  hot weather extremes it makes sense that an accurate measurement, like the wet bulb temperature, is used. 

For now, all we have is the temperature and the “feels like” number that is provided. It seems to me that when checking the weather it’s important to pay attention to both the temperature and the percentage of humidity (I have to swipe left in the app that I use to find that). Become your own weather specialist. Watch for the combination of high numbers for both. Hot and humid means your body won’t be able to cool itself. Extreme heat is not our friend.

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