One day of extreme heat could kill 3,400 people in India, study warns

As temperatures crossed 45°C across large parts of India in the summer of 2026, a new study has revealed the staggering human cost of extreme heat: a single day of severe temperatures could result in about 3,400 excess deaths nationwide, while a five-day heatwave could claim nearly 30,000 lives.

The findings challenge the perception of heatwaves as a seasonal inconvenience, instead portraying them as a major public health threat whose true impact is largely hidden from official statistics.

Researchers arrived at the estimates by using mortality data from earlier studies conducted in 10 Indian cities and applying those findings to districts across the country. Their conclusion is stark: extreme heat is likely killing far more people than currently acknowledged.

A country growing hotter

India has always experienced harsh summers, but heatwaves have become longer, more frequent and more intense in recent years.

In 2024, parts of Rajasthan recorded a scorching 50.5°C, while Delhi experienced some of its hottest nights in years. Similar conditions have returned in 2026, with severe heat alerts issued across Delhi-NCR, Uttar Pradesh, Madhya Pradesh and Rajasthan.

A particularly worrying trend this year has been the rise in unusually warm nights. For millions living in densely built urban areas, concrete structures continue to trap and radiate heat long after sunset, eliminating the brief respite that nights once provided.

The impact is far from equal. Farmers, construction workers, street vendors and other outdoor labourers face prolonged exposure to extreme temperatures, while elderly people and those with existing health conditions remain especially vulnerable.

The deaths that rarely make the count

What makes the study's findings more alarming is how little these deaths feature in official records.

Reported heatstroke fatalities often number only a few hundred, even during severe summers. But many heat-related deaths are never classified as such. Instead, they are recorded as heart attacks, respiratory illnesses or other medical conditions that are worsened by extreme temperatures.

This lack of comprehensive heat mortality data has long obscured the true scale of the crisis and limited public understanding of its consequences.

The study by researchers Piyush Narang and Ashok Gadgil from UC Berkeley attempts to bridge that gap. The authors describe their estimates as conservative lower-bound figures, suggesting the actual death toll could be even higher, particularly in rural areas where access to cooling, healthcare and protective infrastructure is limited.

Among the states examined, Uttar Pradesh emerged as one of the most vulnerable. The researchers estimate that a five-day heatwave could lead to more than 8,000 excess deaths in the state alone.

Districts containing cities such as Ahmedabad, Jaipur and Surat could each record more than 250 additional deaths during a single day of extreme heat.

The study also found that poorer states with lower economic output tend to suffer a disproportionately larger burden, raising concerns about whether the regions most at risk have the resources needed to cope with worsening heat conditions.

A public health emergency in the making

As climate change drives temperatures higher, experts say India must strengthen local early-warning systems, improve healthcare preparedness during heat events and provide targeted support to the communities most at risk.

The study's central message is clear: extreme heat is no longer just a matter of discomfort. It is an increasingly deadly public health emergency, and one whose human cost may already be far greater than official numbers suggest.

With heatwaves expected to intensify in the years ahead, the researchers argue that better preparation today could save thousands of lives tomorrow.