Delhi’s heat stress linked to thousands of unrecognised deaths: report

Delhi’s intensifying heat stress has been linked to thousands of unrecognised deaths over the past decade, with the homeless and outdoor workers bearing the worst brunt, according to a new study released by Greenpeace India on Monday.

The report, titled Death and Degree: Establishing a Relationship of Death and Heat in Scorched Delhi, uses the Universal Thermal Climate Index (UTCI) to demonstrate how rising thermal stress is fuelling a surge in mortality, particularly during the summer and monsoon months.

“Delhi’s heat crisis is extending well beyond summer into the monsoon, creating a prolonged season of danger. The data shows a clear and undeniable link between rising thermal stress and thousands of preventable deaths,” said Selomi Garnaik of Greenpeace India.

Key findings from the study

The study found that monsoon months, traditionally considered a respite from heat, are now marked by persistently high UTCI values: 33.6°C in June, 32.4°C in July, and 31.9°C in August (2015–2024). High humidity has made sweating—a natural cooling mechanism—less effective, exacerbating heat stress.

Between 2019 and 2024, July and August recorded mean UTCI values above 31.5°C, peaking at 34.4°C in July 2019, levels earlier associated with peak summer. The most dramatic rise occurs between March and April, with UTCI jumping by 6.13°C, marking the onset of extreme heat stress.

Deaths appeared to mirror the rise in heat stress. In 2019, Delhi reported 5,341 unrecognised deaths during record UTCI levels in June–August. From 2022 to 2024, the city recorded 11,819 unidentified deaths, the highest three-year toll in recent times. June emerged as the deadliest month, with 657 deaths recorded in June 2019 alone.

The homeless were among the worst affected. In June 2024, 192 homeless people died within just nine days, while July 2024 recorded 401 homeless deaths—the highest in two decades.

Clinical challenges and mortality trends

Dr Manoranjan Ghosh, Assistant Professor of Applied Environmental Science at Symbiosis International University, Pune, noted that linking deaths directly to heat remains difficult. “Since there is no specific sophisticated diagnostic test for heatstroke, certifying deaths directly linked to heat remains a clinical challenge,” he said, while adding that the time-specific mortality pattern nevertheless reveals an undeniable relationship with extreme heat.

Call for policy recognition

The report has urged authorities to recognise heatwaves as disasters under the Disaster Management Act, 2005, which would unlock relief funds, improve preparedness, and ensure accountability. It also recommends including homeless populations and outdoor workers in Heat Action Plans by setting up cooling shelters, hydration stations, and medical outreach programmes.

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In addition, Greenpeace has called for geography-specific heat stress maps and early warning systems in collaboration with the India Meteorological Department to protect Delhi’s most vulnerable residents.