New Delhi: For decades, India has treated extreme heat as a summer problem, with scorching April and May temperatures drawing the most attention. However,
a groundbreaking new study led by the Indian Institute of Technology (IIT) Gandhinagar reveals an alarming shift: the monsoon season may soon become as dangerous as summer for heat stress across the country. The research, which analysed climate data from 1979 to 2021, shows that Uncompensable Heat Stress (UHS) – a physiological threshold where the human body cannot cool down due to extreme heat combined with high humidity has increased considerably in both area and frequency. What was once considered a summer threat is now emerging as a serious monsoon concern, posing significant risks to public health, climate resilience, and labour productivity, especially in vulnerable and densely populated regions like the Indo-Gangetic plain and north-western India.
This changing climate pattern means that millions of Indians could face dangerous heat conditions during July, August, and September – months traditionally associated with cooling rains. Under a 2°C warming scenario relative to pre-industrial levels, monsoon UHS is expected to expand to 58 per cent of India, nearly matching the 60 per cent affected during summer. Keep reading to understand what uncompensable heat stress means for your health, which regions are most at risk, and how India can prepare for this new climate reality that could transform the monsoon from a life-giving season into a health hazard.
What is Uncompensable Heat Stress (UHS)
Uncompensable Heat Stress, or UHS, is not just about high temperatures. It occurs when heat and humidity combine to create conditions so hot and moist that the human body can no longer maintain thermal balance. Normally, we cool ourselves by sweating, when sweat evaporates from our skin, it takes heat away. But when humidity is extremely high, sweat cannot evaporate properly, and our core body temperature keeps rising continuously. Even healthy people doing minimal activity cannot prevent this dangerous rise in body temperature once they cross the UHS threshold. Scientists measure this using wet-bulb temperature, which captures both heat and humidity together.
Monsoon heat stress is rising fast
Currently, heat stress affects around 8 per cent of India during summer (April to June), but only 1 per cent during monsoons (July to September). This balance is shifting dramatically. The study predicts that under 2°C warming, monsoon UHS will expand to cover 53–58 per cent of India which is almost equal to summer levels. The most critical areas include the densely populated Indo-Gangetic Plain, north-western India, and parts of eastern coastal India. These regions already house hundreds of millions of people, making the rise in monsoon heat stress a major public health concern.
Why humid heat is more dangerous than dry heat
Many people in India are aware of dry heatwaves during summer, yet moist heat remains less known and therefore more dangerous. Dry heat allows sweat to evaporate quickly, helping the body cool down. Humid heat, however, saturates the air with moisture, preventing sweat evaporation and blocking the body’s primary cooling mechanism. When wet-bulb temperature reaches around 31°C, the situation becomes extremely dangerous for humans. At 35°C, survival for more than a few hours becomes difficult even for healthy adults resting in the shade. This is why monsoon-driven moist heatwaves can be more lethal than traditional summer heatwaves.
Health Risks: Heatstroke, cardiovascular stress and deaths
Summer UHS is strongly linked to heat-related deaths. Between 1992 and 2020, heatwaves caused approximately 25,000 deaths in India. With monsoon UHS rising, these health risks will extend into the rainy season as well. Experts caution that humid heat environments can lead to rapid overheating, cardiovascular stress, and even heatstroke within hours. The populations most at risk are farm workers in Uttar Pradesh and Bihar, construction labourers in Delhi and Mumbai, the elderly without air conditioning, and the urban poor in areas where concrete retains heat through the night.
What can India do? Early warnings and heat action plans
Researchers emphasise the critical need to limit global warming to 1.5°C and reduce vulnerability to UHS in India, particularly given the growing population and rapid urbanisation. The study shows that moist heatwave risk can be forecast up to four weeks in advance, creating real opportunities to prepare and protect people. India’s heat adaptation strategies such as including early warning systems and heat action plans will need to explicitly incorporate humidity-driven physiological thresholds, not just temperature extremes. Hospitals can adjust staffing, city authorities can open cooling centres, schools can alter hours, and power utilities can prepare for increased grid demand during extremely hot and humid days.
The monsoon season, traditionally seen as India’s cooling relief, is emerging as a major heat stress hotspot due to climate change. With uncompensable heat stress expanding rapidly across space and time, millions will face dangerous humid heat conditions during July to September.
