Wet Bulb Temperature

Context:  India is experiencing a severe heatwave coupled with high wet bulb temperatures. The Dry bulb, Wet bulb, and Dew point temperatures help understand the state of humid air.

What is the Wet bulb temperature?

•    It   is   also   known   as   “isobaric   wet-bulb temperature,”     “thermodynamic     wet-bulb temperature,”     and     “adiabatic     saturation temperature.”
•    Wet bulb temperature is a meteorological term for the lowest temperature that can be reached by evaporating water into the air at constant pressure.
•    It is measured by covering a thermometer bulb with a wet cloth and letting the water evaporate.
•    As the water evaporates, it cools the thermometer, showing the wet bulb temperature.
•    This temperature helps measure humidity affecting things like comfort, farming, and weather patterns.
• The difference between Dry bulb and Wet bulb temperatures depends on the humidity of the air.
•    At  100%  relative humidity,  the wet-bulb temperature is equal to the dry-bulb temperature;  at lower humidity, the wet-bulb temperature is lower than the dry-bulb temperature.

Sate wet bulb temperature

•    Internationally, the agreed-upon safe wet bulb temperature is below 30°C, and the highest limit is 35°C.
•    Between 30°C and 35°C, the human body undergoes hyperthermia, in which the body temperature increases, leading to discomfort and impacts on various organs, including the brain and the heart.

•    Currently, this is not captured in the IMD definition of a heatwave.
•    The dew point is the temperature the air needs to be cooled to (at constant pressure) to achieve a relative humidity (RH) of 100%. At this point, the air cannot hold more water in the gas form.