Traditionally heat stress has been measured via temperature. However, we also know that humidity makes a big difference to heat stress. How big a difference has been a matter of some confusion even among experts.
This note in the Journal of Geophysical Research: Atmospheres explains how different measures of humid heat compare to each other, and when each measure might be most appropriate to use.
The key measures are the “Wet Bulb Globe Temperature” often used to screen for dangerous heat at sporting events and in workplaces, the “Wet Bulb Temperature” beloved of weather geeks, and “Apparent Temperature” quoted to the public by weather services.
The bottom line is that the closer we are pushed to our physiological limits by extreme heat, the more important humidity becomes.
- Commentary: Sherwood, S. C. (2018). How important is humidity in heat stress?. Journal of Geophysical Research: Atmospheres, 123. https://doi.org/10.1029/2018JD028969