India’s struggle with extreme heat may soon extend well beyond the traditional summer months, with new research indicating that dangerous heat-stress conditions are rapidly emerging during the monsoon season and could affect more than half the country under future warming scenarios.
A study by researchers Dipesh Singh Chuphal, Qinqin Kong, Matthew Huber and Vimal Mishra has found that while uncompensable heat stress (UHS) is currently concentrated in the summer season, climate change is expected to drive a sharp rise in hot and humid conditions during the monsoon months, creating a prolonged period of heat-related risk for millions of people.
Uncompensable heat stress refers to environmental conditions in which the human body can no longer effectively cool itself, even through sweating. When heat and humidity combine beyond certain physiological limits, the body’s core temperature continues to rise, increasing the risk of heat-related illnesses, organ failure and death.
The study, titled ‘Emergence of Uncompensable Heat Stress During Monsoon Season in India,’ examined observational data from 1979 to 2021, along with future climate projections. The researchers found that the frequency and geographical extent of UHS have increased significantly across India over the past four decades. Between March and June, about 8 per cent of India’s land area experienced uncompensable heat stress during the study period. In contrast, only around 1 per cent of the country faced similar conditions during the monsoon season from July to October.
The researchers found that summer UHS is most common across the Indo-Gangetic Plain, parts of eastern coastal India and regions along the India-Pakistan border. These areas experience a combination of very high temperatures and moisture, creating conditions that place severe stress on the human body.
However, one of the study’s findings is the projected expansion of heat stress during the monsoon season. Under a global warming scenario of 2°C above pre-industrial levels, UHS is expected to affect about 60 per cent of India’s land area during summer and 53 per cent during the monsoon season, making the two seasons nearly comparable in terms of heat-related risk.
The reason lies in humidity. While summer heat stress is often driven by extremely high temperatures, monsoon heat stress is expected to arise from the combination of moderately high temperatures and very high humidity. Such conditions reduce the body’s ability to cool through the evaporation of sweat, making even lower temperatures potentially dangerous.
According to the study, if global warming reaches 4°C, monsoon-season UHS could become even more frequent than summer UHS in several parts of the country. Regions that currently experience little or no uncompensable heat stress, including parts of central, western and northeastern India, are projected to face these conditions in the future.
The research also explored the relationship between heat stress and mortality. Using data compiled by the National Disaster Management Authority (NDMA) and the India Meteorological Department (IMD), the study found a clear association between summer UHS and heat-related deaths.
More than 25,000 heat-related deaths were reported across the Indian subcontinent between 1992 and 2020. States such as Andhra Pradesh, Uttar Pradesh, Bihar, Rajasthan and Odisha recorded some of the highest mortality figures. The year 2015, which witnessed one of India’s deadliest heatwaves, recorded more than 2,000 heat-related deaths.
The researchers note that official mortality figures likely underestimate the true toll of extreme heat because of reporting gaps and inconsistencies between agencies. Nevertheless, the analysis showed that years with more widespread uncompensable heat stress generally recorded higher heat-related mortality.
The future implications are significant. The study estimates that between 800 million and 1.2 billion people could be exposed to uncompensable heat stress under different warming scenarios. The Gangetic Plain, northwestern India and eastern coastal regions have been identified as major hotspots because of their large populations, socio-economic vulnerabilities and limited adaptive capacity.
Beyond health impacts, prolonged heat stress could affect labour productivity, agriculture, construction, manufacturing and other sectors that depend heavily on outdoor work. The researchers warn that the emergence of dangerous heat conditions across both summer and monsoon seasons could place additional pressure on healthcare systems and local economies.
The study also raises questions about the adequacy of existing heat action plans, many of which focus primarily on temperature while paying less attention to humidity. The authors argue that future heat-warning systems should incorporate both factors to better assess real-world risks.
