Wet Bulb Temperature: Explained: India Heatwaves and the role humidity plays in making them deadly

What is the News?

Parts of India are under a record-breaking heatwave exposing more than a billion people to dangerously hot conditions with little relief in sight.

While temperatures in the region cooled slightly this week, blistering heat is expected to return in the coming days where rising “wet-bulb temperatures” could threaten the ability of humans to survive.

What is Wet Bulb Temperature?

Wet-bulb temperature measures the combination of heat and humidity which can hamper the human body’s ability to cool itself down if at too high a level.

Humans, like most mammals, cool themselves through sweating. Body heat is used to convert sweat into water vapour, and as that evaporation process occurs, the body cools.

However, when the wet-bulb temperature exceeds the temperature of the human body — around 97 degrees Fahrenheit or 36 degrees Celsius — sweat cannot evaporate and humans can no longer cool themselves down.

IPCC on Wet Bulb Temperature

According to the IPCC Report, sustained exposures to wet bulb temperatures above 35°C are fatal, while sustained exposures to wet bulb temperatures above 32°C are dangerous for intense physical activity.

Note: Wet-bulb temperatures in excess of 35°C have been observed in Sindh in Pakistan, but such conditions occur once every three to four years and probably for a few hours. This fails to meet the criteria of “sustained exposure”.

Wet Bulb Temperature in India

According to the IPCC Report, wet-bulb temperatures in India at present rarely exceed 31 degrees C with most of the country experiencing maximum wet-bulb temperatures of 25-30 degrees C.

The report also notes that if emissions are cut, but only by the levels currently promised, many parts of northern and coastal India would reach extremely dangerous wet-bulb temperatures of over 31 degrees C towards the end of the century.

However, if emissions continue to rise, wet-bulb temperatures will approach or exceed the unsurvivable limit of 35 degrees C over much of India with the majority of the country reaching wet-bulb temperatures of 31 degrees C or more.

Source: The post is based on the article “Explained: India Heatwaves and the role humidity plays in making them deadly” published in Indian Express on 9th May 2022