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Bengaluru: A single-day heatwave can cause around 3,400 excess deaths every year in India, and that number can climb to around 30,000 during a prolonged, five-day heatwave, according to a study published on May 26.

These numbers are far higher than figures quoted by the Indian government on multiple occasions. 

Researchers studying heat and its impacts in India told The Wire that even the estimates listed by the study could be conservative. Despite this, the study is an important start to a much-needed conversation on the real impacts of heatwaves – impacts that will otherwise remain invisible, because India undercounts heat deaths drastically, they said.

Heatwaves are periods of unusually hot weather that can impact human health adversely. According to the India Meteorological Department (IMD), a region in India is classified as witnessing a heat wave when the maximum temperature reaches at least 40º C or more if it is located in the plains, or at 30º C or more in the hills. The IMD also declares a region to be experiencing a heat wave when its temperature departs from normal by 4.5º 6.4º C. If the departure from normal is more than 6.4º C, the region is said to be witnessing a ‘severe’ heat wave. Parts of northwest and central India including Delhi have been reeling under a heatwave since May 17.

Heat can also kill. Hot days, unusually warm nights, high humidity and different combinations of these can create an environment that can be fatal for people, especially vulnerable sections such as the elderly. 

In 2024, a large team of scientists affiliated with 14 institutions across the world including the Delhi-based Centre for Policy Research, Ashoka University and the National Research Development Corporation India analysed the association between deaths and daily mean temperatures across ten Indian cities from 2008 to 2019. They defined an extreme heatwave as two consecutive days with an intensity above the 97th annual percentile: meaning, that for two  consecutive days, the daily temperature was hotter than 97% of all historically recorded temperatures for that specific location.

They found that such a two-day heatwave was associated with a 14.7% increase in daily mortality. Heatwaves caused around 1116 deaths annually in these ten cities alone.

Huge increase........

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