Weather conditions greatly affect the way we go hiking. Appropriate clothing helps prepare for bad weather: sun, rain, snow or wind. These have a significant impact on the temperature our body feels during exertion and at rest. In this article, we explain what perceived temperature is and how to manage it while hiking.
Definition of perceived temperature
Perceived temperature is an index used to prevent extreme cold or heatwaves. It takes into account the measured temperature, wind speed and ambient humidity. The Futura Sciences article helps explain the difference between perceived temperature and ambient temperature (which is measured in a shelter from wind, sun and precipitation).
The first perceived temperature index is wind chill (or the Wind Chill effect). It corresponds to the sensation of cold produced by the wind at a given ambient air temperature. Simply put, the body expends energy to create a layer of warm air on the surface of the skin. When there is wind, this layer is swept away, the skin comes into direct contact with the wind and a sensation of cold is produced. The perceived temperature is therefore the sensation of cold you will experience while hiking when there is wind.
Another index similar to wind chill is the Humidex factor. It was created to measure the risks to the human body in cases of excessive heat and humidity. Indeed, humidity makes the evaporation of your sweat less effective, and the risk of discomfort increases.
Calculating perceived temperature
Wind chill is calculated between +10°C and -50°C. The table below helps understand the perceived temperature based on a given temperature and wind speed. These figures can vary between individuals, as perceived temperature differs according to age, fitness level and body type. On the table, the darker the colours displayed, the higher the risk of frostbite.
By studying the table, we can conclude that:
- The higher the wind speed, the greater the perceived cold.
- The colder it is, the greater the influence of wind.
- Even a lightweight wind can affect body temperature.
The Humidex factor is based on ambient temperature, vapour pressure and the dew point. It is a dimensionless index that indicates the risk posed by extreme heat. It ranges from below 30 (no discomfort) to above 54 (heat stroke is imminent).
Dealing with perceived temperature
In France, conditions are not as harsh as in North America, where the Wind Chill effect and the Humidex index are widely used. It is nonetheless essential to check the weather forecast before heading out hiking.
Wear appropriate clothing, cover your skin, protect the extremities of your body — especially the head (a windproof hood helps prevent heat loss). Stay well hydrated and remember to take shelter using natural features when you take a break or set up camp to bivouac.
Never underestimate the weather when hiking or taking part in any other outdoor activity. It is therefore important to factor in the perceived temperature in order to dress accordingly and take certain precautionary measures to avoid suffering from cold or heat.
