This article was originally published by Down to Earth 

Many heat-related deaths go unrecognised or are misclassified. Physicians often record only the immediate medical cause on death certificates, without acknowledging the role of heat as the underlying trigger. Such serious underestimation leads to serious misallocation of resources

Heatwaves have become India’s most dangerous disasters in terms of human mortality. Three of the five warmest years in India have been recorded in the past decade (2015-2024). Heatwaves in India are projected to occur thirty times more often by the end of the century if the global mean temperature increases by 2 degrees Celsius.

Per our estimate (see below), a single heatwave — even one lasting just a few days — causes tens of thousands of excess deaths in India. Despite the rising toll, heatwave mortality remains under-reported, poorly tracked, and largely absent as a target for preventive actions.

Discrepancies in official mortality reports

Between 2000 and 2020, the National Crime Records Bureau (NCRB) reported 20,615 heatstroke deaths, based on its annual Accidental Deaths & Suicides in India reports (NCRB, 2000-2020). During the same period, the National Disaster Management Authority (NDMA) listed 17,767 heatwave deaths, based on state-reported disaster mortality compiled under the Annual Report on Heatwaves in India (NDMA, 2021). In contrast, the India Meteorological Department (IMD) recorded just 10,545 deaths in its Climate Hazards and Vulnerability Atlas of India, using data from State Disaster Management Authorities (IMD, 2022). These figures, all from official government sources, differ by nearly a factor of two, and the discrepancies arise from differences in methodology, data sources, and reporting responsibilities.  Nevertheless, they give the impression that annual excess mortality from heatwaves in India is about 1,500, a tiny number relative to daily all-cause deaths in India of about 25,000.

Peer-reviewed studies suggest the actual death toll from heatwaves is far higher than both official and media counts. Many heat-related deaths go unrecognised or are misclassified. Public health experts note that physicians often record only the immediate medical cause on death certificates, without acknowledging the role of heat as the underlying trigger. As a result, official statistics “barely scratch the surface” of the true human cost of heatwaves.

This undercounting has led to serious inattention in terms of public health response and resource allocation. Without reliable data, there is little basis for targeting adaptation or health preparedness at the right locations. According to an estimate by Zhao et al. (PLOS Medicine 2024), India accounted for 20.74 per cent of global heatwave-related deaths between 1990 and 2019. Another study by Xu et al. (PNAS 2020) estimates that under a high-emissions scenario (RCP8.5), annual heat-related deaths in India would increase 25-fold by 2100, reaching over 1.5 million deaths per year. However, both studies provide projections at broad regional or national scales. They do not offer the district-level granularity needed for targeted policymaking, especially in a country as climatically and socioeconomically diverse as India. Neither study suggests preparatory actions in terms of either policy or infrastructure.

Heatwave mortality at the district level

So far, the only epidemiological estimates of heatwave-attributable mortality in India come from a recent multi-city study by de Bont et al. (Env. International 2024), which analysed the short-term increase in daily mortality during heatwave events in 10 Indian cities. It showed that even a single day of extreme heat can increase mortality by 10-25 per cent, while prolonged five-day events can raise it by over 30 per cent. However, India has over 700 districts, and most of the population lives outside the limits of these 10 cities. To estimate district-level increases in mortality, we extrapolated the findings of de Bont et al. to all districts of India. We combined city-specific heat-mortality risk coefficients with district-level population and mortality data, along with district-level climate classification based on Köppen–Geiger zones. Following de Bont et al, we defined heatwaves using a percentile-based approach: any day where temperatures exceed the local 97th percentile (based on 2008-2018 data) counts as an extreme heat event. We also took into account the average altitudes of districts and their geographical location in assigning their climate profile to the most appropriate city from the 10 cities considered by de Bont et al. We assume that the incremental increase in district mortality is equal to that of the city to which the district is matched. We selected two scenarios from de Bont et al: a single-day heatwave, and a prolonged five-day heatwave.

Our analysis yields the first district-wise estimates of heatwave-induced excess mortality in India. The results are significant:

●       A single day of heatwave across India leads to an estimated 3,400 excess deaths nationally.

●       A single five-day heatwave leads to approximately 30,000 excess deaths, distributed across rural and urban districts.

●       Assuming five heatwaves of five-day duration each summer, our analysis estimates a conservative lower bound of approximately 1,50,000 excess deaths each summer  across India. This figure likely understates the true burden, as the de Bont estimates are based on data from the pre-2018 decade, and both the frequency and intensity of heatwaves are projected to significantly increase  in the coming years.

●       The six worst-affected districts are Ahmedabad, Jaipur, Prayagraj, Patna, Kanpur, and Lucknow — each experiencing more than 180 additional deaths during a single five-day heatwave. Among the states, Uttar Pradesh alone accounts for over 8,000 deaths per heatwave, the highest among all states, followed by Bihar, Madhya Pradesh, Rajasthan, and Gujarat.

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