Heat Index Vs Wet Bulb Globe Temperature

As temperatures warm, our bodies experience the heat differently when outdoors. Two ways of measuring how our bodies deal with heat are the Heat Index and the Wet Bulb Globe Temperature. But what are they, and how are they different?

Most people are familiar with the Heat Index, which takes humidity into account when the temperature reaches 80 degrees Fahrenheit or higher. This "apparent temperature" is used to measure how your body feels the effects of the heat in shady conditions with light wind.

The Heat Index is representative of how efficient your body is able to sweat and cool. As humidity levels increase, it becomes harder for your body to cool from sweating. The sweat takes longer to evaporate, and the slower evaporation is what causes the air to feel hotter than it actually is.

In contrast to the Heat Index, the Wet Bulb Globe Temperature (WBGT) attempts to use more variables to provide a more accurate reading of the heat load your body experiences while outdoors. In addition to looking at the relationship of temperature and humidity, the WBGT also accounts for cloud cover, wind speed, and the sun angle.

The WBGT is important because it better reflects what people will actually experience when active outdoors. This is especially true for athletes and people who work outdoors, when staying in a shaded area all day is not an option.
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Story Image: The differences between the Heat Index and Wet Bulb Globe Temperature are outlined in this graphic. (NOAA, NWS)