What is “wet bulb temperature” and why does it matter?

Question

What is “wet bulb temperature” and why does it matter?

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Answer 1

The “wet bulb temperature” is simply a temperature scale that takes in to account the relative humidity.

Relative humidity and temperature are basically the main two factors that determine whether or not someone will die to prolonged heat exposure. As relative humidity increases, the body is less able to cool off through sweat since evaporation occurs at a slower rate.

Wet bulb temperature matters in the sense that its the easiest way to compare if a certain area is approaching a lethal temperature, because various areas in the globe differ drastically in their average relative humidities.

**A more technical explanation will follow beneath this line**

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When water goes from liquid form to vapor (evaporation), this will cool the surface that the water was resting on. Therefore, if you take a thermometer and cover the bulb of it with a damp cloth, the thermometer will read a lower temperature since water is evaporating on the thermometer surface.

This temperature is the wet bulb temperature.

For example, say that you are in a completely dry desert at 110 degrees F. If you then covered the thermometer bulb with a wet cloth, the temperature would decrease pretty significantly as the water on the cloth would evaporate quickly. This lower temperature (lets just say its 90 F) would then be the “wet bulb temperature”.

The evaporation rate of water in an environment is determined by numerous factors, but probably the most powerful factor is the relative humidity. At 100% relative humidity, there will be no net evaporation that occurs and therefore the thermometer will not be cooled by wrapping the bulb in a wet cloth. At 100% relative humidity, the real temperature and the wet bulb temperature are equal.

So in other words, the higher the wet bulb temperature is, one can deduce that some combination of either the real temperature or the relative humidity is very high.

A wet bulb temperature of 95 F is lethal with prolonged exposure to the average human.