A new study has warned that India's monsoon season is emerging as a major hotspot for heat stress, potentially becoming as hazardous as the pre-monsoon summer due to climate change. The research, published in the journal Nature, indicates that the country may need to revamp its heat adaptation strategies to address the growing threat.
Uncompensable Heat Stress Expanding Rapidly
Researchers from the Indian Institute of Technology (IIT) Gandhinagar found that uncompensable heat stress (UHS), a physiological threshold beyond which the human body can no longer maintain thermal balance, is expanding rapidly across India in both space and time. UHS takes into account air temperature and humidity. Beyond this threshold, even healthy individuals performing minimal activity cannot prevent a continuous rise in core body temperature.
Shift from Dry to Humid Heat
While India's extreme heat burden has traditionally been associated with the dry, pre-monsoon summer (March–June), the study finds that the country is entering a new phase in which hot and humid monsoon conditions are becoming equally important. The research, published on June 5, analyzed historical mortality records from the National Disaster Management Authority and the India Meteorological Department, along with multi-model climate projections.
Significant Increase in UHS
The study found that UHS has already increased significantly between 1979 and 2021. At present, summer conditions dominate heat stress exposure, affecting around eight percent of India, compared to just one percent during the monsoon. However, this balance is expected to shift sharply. Under a 2 degrees Celsius warming scenario relative to pre-industrial levels, monsoon-season UHS is projected to expand to about 53 percent of India — nearly matching the 60 percent affected during summer. This change is driven largely by a rise in hot-humid extremes rather than dry heat alone.
Health Risks and Vulnerable Regions
According to the researchers, monsoon heat stress is no longer negligible in a warming climate. The humid conditions, previously considered less lethal than dry heat, may increasingly breach physiological thresholds that prevent cooling through sweat evaporation. Regions including the Indo-Gangetic Plain, northwestern India, and eastern coastal zones have emerged as persistent hotspots. These areas collectively house more than 700 million people and include populations with high proportions of outdoor workers and limited adaptive capacity, raising concerns about compounding vulnerability.
Need for New Adaptation Strategies
With population exposure projected to rise sharply and UHS to become a year-round phenomenon under higher warming levels, the researchers emphasized that India's heat adaptation strategies — including early warning systems and heat action plans — will need to explicitly incorporate humidity-driven physiological thresholds and not just temperature extremes. By linking historical UHS patterns to observed mortality, the researchers showed that summer-season UHS has a larger share of heat-related deaths than monsoon conditions. This suggests that current health impacts are still dominated by pre-monsoon heat waves, but this relationship may soon change as monsoon heat stress intensifies.
