wet-bulb depression

Wet-bulb depression is the difference between the dry-bulb temperature and the wet-bulb temperature. The dry-bulb temperature measures the actual air temperature, while the wet-bulb temperature indicates the lowest temperature achievable through water evaporation.12

A wet-bulb thermometer has its bulb covered in a wet cloth. As air moves over it, water evaporates from the cloth. This evaporation process absorbs heat, causing the wet-bulb thermometer to register a lower temperature than the dry-bulb thermometer. The drier the air, the faster the evaporation, and the greater the temperature difference, known as the wet-bulb depression. This depression is a key factor in determining air humidity and is also used to assess the risk of heat stress for humans, as it mimics the body's cooling through perspiration. When the air is fully saturated (100% humidity), there is no evaporation, and the wet-bulb and dry-bulb temperatures are equal.23