IAS Gyan

Daily News Analysis

Humid Heat Extremes

5th July, 2024 Environment

Humid Heat Extremes

Source: Indian express

Disclaimer: Copyright infringement not intended.

Context: People in India exposed to extreme levels of humid heat during monsoons increased by at least 67 crore over the period 1951-2020, a research has found.



In general, there are two kinds of heat: dry heat, in which relative humidity levels are at or below 40%, and humid heat, in which relative humidity levels are above 40% and can reach (rarely) 100%.

Humid Heat

  • Humid heat results from high temperatures and high levels of moisture in the air. typically with a temperature at or above 32.2 C and a relative humidity of 40% or more.
  • Humid heat tends to be more dangerous as the moisture does not evaporate as efficiently, making it harder for the body to cool off ,so more heat remains in the body.
  • As a result, it can “feel” hotter than the same temperature in a dry environment.
  • Commonly associated with tropical areas.

Dry Heat

  • Dry heat occurs in any location with a combination of a temperature of 32 ° C or above and relative humidity of 40% or less.
  • Dry heat occurs most often in desert climates and areas receive very little rain and moisture.
  • Dry heat allows the body to cool more quickly, so you are less likely to get heat stress in an arid environment.
  • Dry air allows more efficient evaporation than humid air, which is usually feel cooler in dry air as it has less moisture.

Humid heat metrics

  • Humid heat metrics vary in several ways, including which humidity metric used. Common humid heat metrics like the heat index and wet bulb globe temperature are both based on relative humidity.

Humidity is a measure of how much water vapor there is in the air.

There are two primary definitions of humidity:

Specific humidity is a measure of moisture content—how much water vapor there is relative to the total moist air mass.

Relative humidity is a measure of how saturated the air is—how much water vapor the air contains compared to the maximum it could contain at a given temperature. 

Global warming and humid extremes

  • Global warming has significantly increased days of hot-and-humid extremes to 10 between 1951 and 2020.
  • Area exposed to extreme and detrimental wet-bulb temperatures exceeding 31 degrees Celsius increased by close to 43 million square kilometres – representing over 67 crore people.
  • The increase in moist heat can directly impact about 37-46 million people living over the Indo-Gangetic plain.
  • The humid and hot conditions during monsoons are a significant challenge to the health and well-being of the people of India, especially to physical labour.

Economic Impact

  • Study find a 3 degrees Celsius increase in global warming can reduce labour productivity by 7 per cent and contribute to at least 4 per cent reduction of GDP in India, which leads to inflation in crop prices.

Dry Bulb Temperature

Wet Bulb Temperature

The Dry Bulb Temperature refers basically to the ambient air temperature. It is called "Dry Bulb" because the air temperature is indicated by a thermometer not affected by the moisture of the air.

When people refer to the temperature of the air, they are normally referring to its dry bulb temperature.

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.

The wet bulb temperature is always lower than the dry bulb temperature but will be identical with 100% relative humidity.

More: https://www.iasgyan.in/daily-current-affairs/humid-heat-waves-in-india


aletenutrition.com,EconomicTimes,New York Times.


Q. Establish a relation between climate change, extreme weather events and socio-economic impact. 200 words.