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How heat stress has increased in urban India this year
Summary
Nearly 85% of the 65 cities analysed, experienced an increase in heat stress hours in May compared to the same period last year. Among these, six recorded over 100 hours of heat stress, matching the levels observed in May 2023.NEW DELHI : Ten of India’s 65 cities with over a million population experienced more than 100 hours of ‘heat stress’—dangerous levels of both heat and humidity—in May, in the midst of India’s longest election season, data analysed by climate tech startup, Respirer Living Sciences, showed.
Heat stress refers to situations when the heat index, which accounts for both surface temperature and humidity, exceeds 41°C. This condition strains the body’s ability to regulate its internal temperature and can severely impact work productivity, and the report shows that this has grown significantly this month as compared to May 2023 in some of India’s largest cities.
Over the past few decades, India has been experiencing higher temperatures more frequently and earlier than usual, accompanied by extended periods of longer and more intense heat waves and higher humidity levels. This combination of intense heat and humidity during the prolonged summer months is leading to increased heat stress across several regions in India.
While nine of the 65 cities analysed showed nil hours of heat stress, 55 others recorded an increase in the heat stress hours during May - typically considered the peak summer month.
Nearly 85% of the 65 cities analysed, experienced an increase in heat stress hours compared to the same period last year. Among the cities that witnessed the most significant rise, three major cities in Gujarat and Mumbai endured over 100 hours of heat stress. Several other cities, including Visakhapatnam, Puducherry, Bhubaneshwar, Chennai, Kolkata, and Vijayawada, also recorded over 100 heat stress hours, matching the levels observed in the previous year.
The report further categorised heat stress into two categories: humid heat stress (when relative humidity exceeds 50%) and dry heat stress (when relative humidity is below 50%).
According to the report, humid heat stress was particularly high in coastal cities due to already high humidity levels. 37 of the 65 cities did not witness a situation of humid heat stress.
While the condition was severe at the beginning of May for several coastal cities, many experienced some relief by the fourth week ending on May 26. Still, 13 of the 28 other cities that observed humid heat stress hours recorded an increase in heat stress hours between the first and fourth weeks of May.
Although lower humidity is considered relatively better, an analysis of cities experiencing dry heat stress showed that the number of heat stress hours increased in more inland cities. 14 cities analysed did not experience dry humid heat stress hours. Among the other 51 cities, about 60% witnessed a rise in the number of heat stress hours over the first four weeks of May.
