Extreme Heat and Human Health in India: A Silent Threat in the Era of Climate Change

Dear Readers,

Climate change is increasingly transforming extreme heat from a seasonal environmental phenomenon into a major global health emergency.¹ India, because of its large population, tropical climate, rapid urbanisation and socioeconomic disparities, is among the countries most vulnerable to the health consequences of rising temperatures and recurrent heatwaves.² In recent years, extreme heat events across India have become more frequent, prolonged and severe, posing escalating threats to human health, healthcare systems, labour productivity and economic stability.² Given that India is home to approximately 18% of the world’s population, the health impacts of climate change and extreme heat in the country have implications not only for national public health but also for global health outcomes and resilience efforts.

According to the India Meteorological Department (IMD) and recent seasonal forecasts, India experienced widespread above-normal temperatures and prolonged heatwave conditions during the summer of 2026, particularly across northwestern, central and eastern regions.^3-5 Several states, including parts of Maharashtra, Uttar Pradesh, Punjab, Haryana, Rajasthan and Madhya Pradesh, recorded temperatures exceeding 45°C, with Brahmapuri in Maharashtra reaching 47.2°C in May 2026.⁴ The IMD further warned of increasing heatwave duration, warmer nighttime temperatures and above-normal heatwave days across multiple regions of India during the April–June 2026 season.⁵ Recent climate analyses suggest that under high-emission scenarios, heatwave days across India may increase three- to fourfold by the end of the century, substantially increasing risks of heat-related morbidity and mortality.⁶ A major concern is the increasing occurrence of wet-bulb temperatures, which reflect combined heat and humidity exposure. Unlike dry heat, elevated wet-bulb temperatures impair the body’s ability to cool through sweating. Studies suggest that sustained wet-bulb temperatures above 35°C may exceed human physiological tolerance, even among healthy individuals.⁷ South Asia, including India, is considered one of the global hotspots most vulnerable to such extreme humid heat events.^2,7

Several climatic and environmental mechanisms contribute to India’s escalating heat burden. Persistent high-pressure atmospheric systems may trap warm air, reduce cloud formation and promote continuous solar heating over multiple days. Simultaneously, El Niño-associated climatic variability can weaken monsoon patterns and intensify drought and heat conditions. Urbanisation further amplifies temperatures through the urban heat island effect, where concrete infrastructure, asphalt surfaces, vehicular emissions, reduced vegetation and air-conditioning exhaust trap heat within densely populated cities.^8,9 Urban temperatures may remain several degrees higher than surrounding rural areas, particularly during nighttime.⁹ Warm nighttime temperatures represent an especially dangerous yet underrecognised phenomenon. Historically, cooler nights allowed physiological recovery from daytime heat exposure. However, many Indian cities are now experiencing persistently elevated nighttime temperatures, producing cumulative heat stress and increasing cardiovascular and metabolic strain. Several studies have linked higher nighttime temperatures with increased mortality, sleep disruption, renal stress and cardiovascular events.^9,10

The health consequences of extreme heat extend far beyond classical heatstroke [Table 1]. Acute heat-related illnesses include dehydration, heat cramps, heat exhaustion, electrolyte imbalance, syncope and heatstroke, which may rapidly progress to multiorgan dysfunction and death if untreated.^1,2 However, extreme heat also substantially exacerbates chronic diseases. Cardiovascular morbidity increases because heat exposure promotes dehydration, vasodilation, tachycardia, thrombosis and increased cardiac workload. Heatwaves have been associated with increased hospitalisations and mortality from ischaemic heart disease, heart failure, arrhythmias and stroke.^11,12 Renal health is similarly affected. Recurrent dehydration and occupational heat exposure contribute to acute kidney injury and progression of chronic kidney disease, particularly among agricultural and construction workers.¹³ India’s large informal workforce remains highly vulnerable because millions of individuals work outdoors with limited access to hydration, cooling and occupational protections.^11-13 Respiratory illnesses may worsen during heatwaves because high temperatures contribute to ozone formation, air pollution and wildfire-associated particulate exposure. Heat exposure has also been associated with adverse mental health outcomes, including anxiety, irritability, aggression, sleep disturbances and increased psychiatric admissions.¹⁴ Pregnant women, children, older adults and individuals with chronic diseases remain disproportionately vulnerable to heat-related morbidity and mortality.^10,14

The healthcare implications are substantial. Heatwaves increase emergency department visits, hospital admissions, intensive care utilisation and healthcare workforce strain.¹¹ Electricity shortages, cooling failures and disruptions in water supply may further compromise healthcare delivery during extreme heat events. Importantly, heat-related mortality in India is likely significantly underestimated because many deaths occurring during heatwaves are attributed to cardiovascular, renal or respiratory diseases rather than heat exposure itself.¹⁵ Inadequate surveillance systems and inconsistent death certification practices further contribute to underreporting.

Recent evidence highlights the scale of the problem globally. The 2023 Lancet Countdown on Health and Climate Change reported that the average annual heat-related mortality among adults older than 65 years increased by approximately 85% during 2013–2022 compared with 1991–2000, driven by both population aging and rising global temperatures.¹⁶ In India, heat exposure also has major economic consequences. A World Bank report estimated that productivity losses from rising heat and humidity could place nearly 4.5% of India’s GDP at risk by 2030, particularly affecting labour-intensive sectors such as agriculture and construction.¹⁷ India has initiated several important adaptation measures, including Heat Action Plans (HAPs), early warning systems and public awareness campaigns. The Ahmedabad Heat Action Plan, introduced after the devastating 2010 heatwave, is widely regarded as a successful model for reducing heat-related mortality through coordinated public health interventions, surveillance, interagency collaboration and risk communication.¹⁸ However, implementation of HAPs remains inconsistent across states, and many regions continue to lack adequate preparedness infrastructure.

Urgent policy interventions are now necessary. First, climate-resilient healthcare systems must become a national priority.¹⁹ Hospitals require reliable cooling infrastructure, emergency heat protocols, resilient electricity systems and healthcare worker training in recognition and management of heat-related illnesses. Second, urban planning policies should prioritise green spaces, reflective roofing, sustainable housing and reduction of urban heat islands.⁹ Third, occupational protections for outdoor workers, including mandatory hydration access, shaded rest periods and modified work schedules during extreme heat, must be strengthened. Improved surveillance and research are equally important.²⁰ Heat-related illnesses and mortality should be systematically monitored through integrated climate-health surveillance systems.¹⁵ Public health messaging must expand beyond heatstroke awareness alone to include chronic disease risks, nighttime heat exposure, hydration and community-level adaptation strategies. Finally, climate adaptation should be integrated into broader public health and disaster preparedness policies at national and regional levels.²⁰

In conclusion, extreme heat is no longer merely an environmental concern but a rapidly escalating medical and public health emergency. As climate change accelerates, India will increasingly face severe heat exposure, with profound implications for population health, healthcare infrastructure and socioeconomic resilience. Recognising heat-related illness as a major healthcare priority is essential to reducing preventable morbidity and mortality in the warming decades ahead. As the world’s most populous nation, India’s response to extreme heat will have consequences that extend beyond its borders. Targeted interventions, including HAPs, climate-resilient healthcare systems, urban heat mitigation strategies and protection of vulnerable populations, have the potential to improve health outcomes for hundreds of millions of people while generating scalable models for other climate-vulnerable regions worldwide. Investments in heat resilience in India, therefore, represent not only a national priority but also an opportunity to advance global public health and climate adaptation efforts.