August 26, 2016.
Being hot can be perfectly bearable as long as there are points of shade and a little air. On the other hand, if this heat is humid, our organism supports it much less well. How to explain it?
The body cools down with perspiration
A few hours before a thunderstorm, the heat is hardly bearable. It is more overwhelming, it weighs our whole body down and seems to tire us much more than dry heat. This sensation is in fact due to our thermoregulatory mechanism, which works less well when the temperature is high and the atmosphere humid.
Why ? It is actually very simple. When it is hot, the body expels excess heat through perspiration, thanks to a phenomenon of skin evapotranspiration. When the ambient air is not humid, this evaporation takes place very easily. On the other hand, if the surrounding air is saturated with water vapor, the water in the body cannot evaporate as easily.
Moisture in the air prevents skin evapotranspiration
This is why, in a tropical country for example, perspiration runs down the body and the body temperature rises much more than in a dry atmosphere. The body will therefore find it much more difficult to withstand a temperature of 25 ° C in a humid environment than at 35 ° C in a dry environment..
The Meteorological Services of Canada have developed a heat index, called Humidex, which is calculated based on outdoor temperature and humidity. ” A humidx of 40 with, for example, a temperature of 30 degrees means that the feeling of heat in humid air at 30 degrees would be more or less the same as in dry air at 40 degrees. », Explains a Canadian weather website. This index does not exist in France, but it helps us better understand a phenomenon that we often encounter.
Read also: Recommendations in case of hot weather
