In May, India experienced heightened heat stress conditions, with ten of its 65 million-plus population cities enduring over 100 hours of exposure. This perilous combination of heat and humidity, known as heat stress, arises when the heat index surpasses 41°C, challenging the body’s ability to regulate its internal temperature. The report indicates a substantial increase in heat stress hours compared to May 2023 in major Indian cities.
Over the past few decades, India has witnessed a surge in both the frequency and intensity of higher temperatures, leading to extended periods of more intense heatwaves and elevated humidity levels. The confluence of extreme heat and humidity during the protracted summer months has resulted in escalating heat stress levels across various Indian regions.
Out of the 65 cities examined, nine cities recorded no heat stress hours, while the remaining 55 experienced an increase. A notable 85% of the cities analyzed endured more heat stress hours compared to the same period in the previous year. Among the cities with the most significant increase, three major cities in Gujarat and Mumbai faced over 100 hours of heat stress. Other cities like Visakhapatnam, Puducherry, Bhubaneshwar, Chennai, Kolkata, and Vijayawada also recorded similar excessive heat stress hours.
The report categorizes heat stress into two types: humid heat stress (relative humidity exceeding 50%) and dry heat stress (relative humidity below 50%). Humid heat stress was particularly severe in coastal cities due to their inherently high humidity levels. Thirty-seven cities did not experience humid heat stress, and while the condition was initially severe in coastal cities in early May, many reported some improvement by the fourth week ending on May 26. Nonetheless, 13 of the 28 cities that observed humid heat stress hours experienced an increase between the first and fourth weeks of May.
While lower humidity is generally more bearable, the analysis of cities experiencing dry heat stress revealed an increase in heat stress hours in more inland cities. Fourteen cities did not experience dry heat stress, and of the remaining 51 cities, approximately 60% witnessed a rise in the number of heat stress hours over the first four weeks of May.
