Wet Bulb Temperature

• Context (NDTV): 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.
• 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.