Rising Threat of Humid Heat in India
A new analysis by Climate Central reveals that India has experienced a significant increase in dangerous humid heat days, rising from an average of 101 days per year during the 1970s to 141 days per year between 2016 and 2025. A dangerous humid heat day is defined when the daily maximum wet-bulb temperature reaches 25 degrees Celsius or higher. This measure combines heat and humidity to indicate the environmental stress on the human body.
Health Risks of Humid Heat
The rise in such days is particularly dangerous because humid heat compromises the body's primary cooling mechanism—sweating. When humidity is high, sweat evaporates less efficiently, making it harder for the body to cool down. This can lead to heat-related illnesses, including heat exhaustion, heatstroke, and exacerbation of cardiovascular and respiratory diseases. According to the analysis, prolonged exposure to high wet-bulb temperatures can be fatal.
Global Trends and Attribution
India is not alone in facing this trend. Globally, dangerous humid heat days have more than doubled from 10 days per year in the 1970s to 23 days per year between 2016 and 2025. The largest increases have been observed in tropical humid regions, where wet-bulb temperatures are naturally higher and closer to the dangerous threshold. The analysis attributes 64% of global dangerous humid heat days since 1970 to human-caused climate change.
Climate Change as the Primary Driver
“Climate change has gone from a minor contributor of dangerous humid heat days to the primary driver. In some parts of the world, humid heat that once would have been rare or nearly impossible without climate change is now a defining feature, putting the lives of millions at risk,” the analysis stated. This shift underscores the escalating impact of global warming on extreme weather events and public health.
Implications for India
For India, the increase in humid heat days poses a serious challenge to public health, agriculture, and labor productivity. The country's densely populated regions, particularly in the tropical south and along the coasts, are most vulnerable. The analysis calls for urgent adaptation measures, including improved early warning systems, urban planning to reduce heat islands, and policies to mitigate climate change.
