Gathering clouds

The monsoon is regarded as the national cooler, feted in literature and festivals as the season that promises respite from heat. This traditional understanding, however, may not hold anymore. Recent research into India's changing heat dynamics indicates that the months — or even the hours — associated with cooling no longer serve that purpose. Global warming, coupled with anthropogenic interventions, is changing the country's heat dynamics. The emergence of a phenomenon called Nocturnal and Compound Heat Waves, and the shift of Uncompensable Heat Stress (UHS) towards the monsoon months, demonstrate this change.

Scientists warn that unless steps are taken to mitigate and adapt to the changing heat patterns, the ramifications for public health and economic productivity will be severe.

A team from the Indian Institute of Technology (IIT) Gandhinagar studied the impact of different scenarios of rising temperatures over India (bit.ly/Hot-humid) and concluded that UHS — the point at which the human body can no longer lose enough heat to maintain a stable core temperature — is likely to shift towards the monsoon months. At present, UHS impacts 8% of India in summer (March-June) and only 1% between July and October. At a 2°C rise, UHS will affect 60% of India during summer and 53% during the monsoon. A 4°C rise means the monsoon UHS spread will overtake the summer UHS spread.

"Monsoon is peak time for agricultural activity. The decreased capacity of labour at this time will have a major impact," says Vimal Mishra, Dean, Research and Development, at the institute, and corresponding author of the study. Extended heat stress through summer and monsoon will impact labour productivity across sectors. "Dry heat can still be managed with fans, air coolers, and water fountains. High temperature plus humidity requires air conditioning, which is not available to everyone," Mishra says.

Nights are also losing their capacity to serve as recovery periods from heat stress. A survey of 100 Indian Smart Cities indicates heat persisting well into the night, leading to compound heat waves (bit.ly/Night-heat). Published in a special issue of Physics and Chemistry of the Earth, the study notes that "urban heat risk in India is increasingly shaped by diurnal persistence and cumulative thermal burden rather than daytime extremes alone."

Worse, homes — meant to protect humans from extreme weather — are becoming heat traps at night. Homes are the warmest between 8 pm and 9 pm. The indoor temperature peaks to 34.7°C, according to a survey of low- and middle-income homes in Chennai by Climate Trends (bit.ly/hot-homes). The survey, presented at the India Heat Summit 2026 in May in New Delhi, noted that the popular construction materials in India, and poor ventilation and high humidity in the coastal city combined to increase nocturnal thermal discomfort. The results are similar to studies conducted in Ahmedabad and Hyderabad, the survey notes.

Meanwhile, winter is also shortening. A decadal assessment of temperature based on past data and future projections indicates significant warming in India since 1980, with the hottest trend occurring between 2011 and 2020. The winter warming rates are higher than those in summer and monsoon. It projects a substantial increase in the frequency and persistence of dangerous Heat Index (HI) levels, driven by rising temperatures and regionally variable humidity trends. Critical HI days will be highest in coastal regions in winter and more in the North in summer (bit.ly/HI-days).

All studies point to the need to develop action plans, factoring humidity into the country's heat levels. To cool homes passively, the Climate Trends authors suggest measures such as promoting the use of climate-responsive construction materials, including autoclaved aerated concrete, subsidising passive cooling with reflective roofs and pavements, and updating building codes to prioritise ventilation. "We cannot change the climate. We will have to adapt to it," Mishra says.