A single day of extreme heat kills nearly 3,400 people across India. A five-day heatwave kills nearly 30,000. The Indian government, meanwhile, reports roughly 800 heat-related deaths per year.
That gap is not a rounding error. It is a structural failure — and a new study has now put precise, district-level numbers to its scale for the first time.
The research, published May 26 in the peer-reviewed journal Frontiers in Environmental Health, was conducted by Piyush Narang and Ashok Gadgil of the India Energy and Climate Center at the University of California, Berkeley. It is the first study to estimate heatwave-induced excess deaths at district resolution across all of India using publicly available data.
What the Researchers Did
The team built on a 2024 multi-city study that analysed heat-related mortality across ten Indian cities — including Delhi, Ahmedabad, Mumbai, and Kolkata — between 2008 and 2019. That study found a two-consecutive-day extreme heat event was associated with a 14.7 percent increase in daily mortality, causing nearly 1,116 deaths annually in those ten cities alone.
Narang and Gadgil extended those findings nationwide. They matched every Indian district to one of the ten study cities using climate zone classification, then applied corresponding heat-mortality risk coefficients to district-level population and mortality data from India’s Civil Registration System.
“Excess deaths” measures all deaths above the expected baseline during a given period, regardless of stated cause. It is the only metric that captures what official records routinely hide.
Dr. Rakesh Parashar, a medical doctor and health policy advisor working with WHO and World Bank programmes, explained the clinical reality. “Death certificate rules ask doctors to mention immediate medical causes such as ischaemic heart disease or acute kidney failure, which may be precipitated by heat exposure,” he told Dialogue Earth. “Heat can exaggerate cardiac events, especially in the elderly — and that is completely missing in heat mortality data.”
Srinath Reddy, founder of the Public Health Foundation of India, put it plainly to the Associated Press: “Most doctors just record the immediate cause of death. Attribution to environmental triggers like heat is not recorded.”
The Numbers
Under a one-day extreme heat scenario — defined as a day when temperature exceeds the district’s historical 97th percentile — India sees an estimated 3,400 excess deaths. Under a five-day heatwave, that figure rises to nearly 30,000.
With 95 percent confidence intervals applied, the range runs from 2,400 to 4,400 for a single day, and 18,000 to 43,000 for a five-day event. The central estimates hold across the full range.
“This finding indicates that even a one-day exposure to extreme heat can produce a significant increase in mortality at the national scale, much larger than the all-India heat-related excess mortality reported in the press and by government agencies, which remains about 800 per year,” the authors wrote.
The contrast is not subtle. The government’s annual figure is roughly what this study estimates die in a single bad day.
Why the Count Stays Low
India has a structural undercounting problem. When someone dies of cardiac arrest during a heatwave, the death certificate says cardiac arrest. Official statistics depend on heatstroke diagnoses — a category so narrow it captures only direct, immediate heat deaths and misses nearly everything else.
The numbers tell the same story across every agency.
The Ministry of Earth Sciences recorded 3,798 heat deaths between 2018 and 2022. The National Crime Records Bureau counted just 20,615 heatstroke deaths across a full twenty-year period, according to the Indian Express. HeatWatch tracked 733 deaths across 17 states between March and June 2024 alone. The Ministry of Health and Family Welfare, covering those same 17 states in the same period, reported only 360.
Every agency counts differently. None of them counts enough.
India also does not recognise heatwaves as a notified national disaster — an omission that directly limits the emergency funding states can access to respond.
Abhiyant Tiwari, Lead for Climate Resilience and Health at NRDC India and a co-author of the foundational 2024 multi-city study, has seen this gap from the inside. “During the course of our research, we observed that the number of deaths we were estimating during heatwave days in the summer were far higher than what cities were officially reporting,” he said. “This underreporting is because of an absence of robust heat surveillance systems in Indian cities.”
He adds that the data available from all official sources “is only for heatstroke deaths and not all heat-related deaths” — a distinction that renders the government’s annual figures almost meaningless as a measure of true burden.
Where People Are Dying
The burden falls hardest on India’s most populous northern and central states. Uttar Pradesh alone accounts for an estimated 8,100 excess deaths in a five-day heatwave. Bihar follows at approximately 3,615, Madhya Pradesh at 2,964, Rajasthan at 2,664, and Gujarat at 2,354.
These five states, home to 43 percent of India’s population, account for more than 60 percent of total national excess mortality.
At the district level, Ahmedabad carries the highest projected toll at 307 excess deaths per five-day event, followed by Jaipur at 265 and Surat at 261. Districts including Prayagraj, Patna, Lucknow, Kanpur Nagar, Agra, Azamgarh, and Bareilly each exceed 180.
A Crisis the Poor Cannot Afford
The study’s most consequential finding goes beyond the death count. The five highest-burden states contribute only 29 percent of India’s GDP but absorb 66 percent of its heatwave excess deaths — a 2.3-fold disproportion between mortality and economic capacity. The states least equipped to build cooling infrastructure, fund health systems, or design heat action plans are precisely the ones that need them most.
Dr. Akshay Deoras, senior research scientist at the National Centre for Atmospheric Science and the Department of Meteorology at the University of Reading, explains why this matters beyond economics. “Heat disproportionately impacts people — it hits the elderly and children quite a lot, and those who cannot afford cooling spaces,” he said. “But people have to go out to earn bread and butter. If you ask them to stay at home, they are just not going to survive. That is a double problem — and in India, it is a severe one.”
He also flags a danger that barely registers in official monitoring: humid heat. “Humid heat is basically a silent killer,” Dr. Deoras said. “The major focus has been on dry heat, but humid heat is not even on the main agenda of the weather department at the moment — particularly in May, June, and into the monsoon season when moisture levels are high across much of the country.”
The Berkeley study’s estimates may actually miss this threat. It uses dry-bulb temperature thresholds, which means coastal districts experiencing dangerous humid heat can fail to register as heatwave days at all — a limitation the authors themselves acknowledge.
What Needs to Change
Apekshita Varshney, founder and executive director of HeatWatch, a nonprofit tracking heat mortality across India, said the study’s district-level granularity changes how the problem must be framed. “It shows that heat is not a rare disaster, but a frequent and rising killer, concentrated in specific regions that are often poorer and less able to adapt,” she said. “That shifts heatwaves from being treated as occasional weather events to being recognised as a recurring public-health emergency.”
The researchers argue that federal adaptation funding — under the National Disaster Management Authority and the National Action Plan on Climate Change — must be weighted toward high-burden, low-GDP states, not distributed by population or administrative capacity alone.
“The states least able to finance adaptation are precisely those facing the greatest heat mortality risk,” Narang and Gadgil wrote. “Failing to account for this disproportion when sizing and directing heat resilience investments will systematically under-resource the populations most at risk.”
Varshney draws a direct parallel to a turning point in India’s disaster history. The 1999 Odisha cyclone, she said, prompted serious national investment in preparedness, relief, and rehabilitation. Evidence-based heat mortality estimates could do the same. “We must read these numbers as an order-of-magnitude signal of severe undercounting,” she said, “not a precise tally.”
The precise tally, she implied, would be worse.
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