Pune, 24th August 2026: A new study by researchers at the Indian Institute of Tropical Meteorology (IITM), Pune, has found that urban heat exposure in India increased by 157% between 1983 and 2016. The study links the rise to rapid population growth, urbanisation and increasing temperatures.
The research was conducted by Gayatri Kulkarni, Rutuja Bhorade and Thara Prabhakaran from IITM's Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) team. It has been published in the international journal Urban Climate.
The researchers analysed climate and temperature data from more than 3,000 urban settlements across India over 34 years. Instead of looking only at temperature, the study measured how many people were exposed to heat and for how long.
Urban heat exposure rose from 23 billion person-days in 1983 to 59 billion person-days in 2016. Of the overall increase, around 64% was attributed to population growth, while the remaining 36% was associated with rising urban temperatures.
The study found that the reasons behind increasing heat exposure differ from city to city.
In Delhi, population growth accounted for about 74% of the increase in heat exposure. In Mumbai, the share was 54%, while population growth contributed 47% of the increase in Kolkata.
In several coastal cities in southern India, however, rising urban temperatures emerged as the more significant factor behind increasing heat exposure.
This shows that cities cannot rely on a single approach to tackle rising heat risks. Local population patterns, urban development and temperature trends need to be considered while planning heat mitigation measures.
The researchers used the Wet Bulb Globe Temperature (WBGT) index to assess heat stress. The measure takes both temperature and humidity into account, providing a better indication of the impact of hot and humid conditions on the human body.
The study classified WBGT levels above 30°C as very high risk and those above 32°C as extremely dangerous.
Between 1983 and 2016, the frequency of very high-risk heat days increased by 44%. Extremely dangerous heat days more than doubled during the same period.
As a result, people in several parts of the country are now facing hazardous heat conditions for nearly an additional month each year compared with the earlier period.
The researchers highlighted the combined impact of population growth, rapid urbanisation and rising temperatures on heat exposure in Indian cities.
The findings underline the need for city-specific heat action plans, regular heat monitoring, protection for vulnerable populations and urban planning measures that reduce heat.
Rather than adopting the same strategy everywhere, cities need to identify whether population growth, rising temperatures or both are driving their heat exposure and design measures accordingly.