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Wet Bulb Temperature: Important Points

What Is The Wet Bulb Temperature?

Part 2 of the sixth assessment report of Intergovernmental Panel on Climate Change (IPCC), emphasised on the trend in the ‘Wet Bulb’ Temperature in South Asia.

  • The trend will provide an index of the impact of heat and humidity combined — and its effect on health.
  • Wet bulb temperature is the lowest temperature to which air can be cooled by the evaporation of water into the air at a constant pressure.
  • WBT is a limit that considers heat and humidity beyond which humans can not tolerate high temperatures.
  • The Wet Bulb temperature is the temperature of adiabatic saturation. This is the temperature indicated by a moistened thermometer bulb exposed to the air flow.
  • An adiabatic process is one in which no heat is gained or lost by the system.
  • Wet Bulb temperature can be measured by using a thermometer with the bulb wrapped in wet muslin.
  • The adiabatic evaporation of water from the thermometer and the cooling effect is indicated by a “wet bulb temperature” lower than the “dry bulb temperature” in the air.
  • The rate of evaporation from the wet bandage on the bulb, and the temperature difference between the dry bulb and wet bulb, depends on the humidity of the air.
  • The evaporation is reduced when the air contains more water vapour.
  • The wet bulb temperature is always lower than the dry bulb temperature but will be identical with 100% relative humidity (the air is at the saturation line).
  • A wet-bulb temperature of 31°C is exceedingly harmful to humans, while a temperature of 35°C is unsurvivable for more than 6 hours.