The Hidden Climate Shift Making India's Heatwaves More Deadly

By 10 pm, the heat should have loosened its grip. Streets should cool, ceiling fans should finally matter, and exhausted bodies should get a few hours of relief before another punishing day. But across India this summer, the nights are refusing to cool down.

In cities and small towns alike, thermometers are hovering stubbornly near 30 degrees Celsius long after sunset. Bedrooms feel like sealed ovens. Concrete walls radiate the day's stored heat well into midnight. Even sleep- the body's last defence against extreme temperatures- is becoming harder to come by.

India is not just facing hotter summers anymore. It is entering an era of relentless heat.

As temperatures soar past 45 degrees Celsius across large parts of the country, scientists and meteorologists warn that the crisis is no longer defined by daytime highs alone. The danger now lies in the deadly convergence of rising temperatures, warmer nights, increasing humidity, shrinking soil moisture, and expanding urban heat islands- all amplified by climate change.

Data compiled by Climate Trends from multiple scientific and meteorological studies paints a stark picture. Heatwave frequency across India's Core Heatwave Zone (CHZ) has increased by 0.1 days per decade between 1961 and 2020. The duration of these heatwaves has also lengthened by 0.44 days per decade, while severe heatwaves are becoming more frequent and lasting longer.

And when the sun goes down, the heat stays.

India's average night-time temperatures are rising by approximately 0.21 degrees Celsius every decade. According to the Council on Energy, Environment and Water (CEEW), 35 out of 36 states and Union Territories are witnessing increasing nighttime warming trends. In several locations this year, minimum temperatures have remained in the high 20s, with some stations touching 30 degrees Celsius overnight.

That matters more than many realise.

The World Health Organisation recommends indoor temperatures remain below 24 degrees Celsius to reduce heat-related health risks and cardiovascular strain during sleep. But in much of India, especially in dense urban neighbourhoods with limited ventilation or cooling access, homes no longer cool sufficiently at night. For millions of people - particularly outdoor workers, low-income families, the elderly, and those without air conditioning - there is simply no escape.

Banda in Uttar Pradesh recently recorded 48 degrees Celsius, among the highest temperatures in the country this season. Delhi, Rajasthan, Madhya Pradesh, Bihar, Odisha, Telangana and large parts of central and north India continue to remain under intense heatwave conditions as hot north-westerly winds sweep in from Rajasthan and the Sindh region of Pakistan.

"In the absence of any weather system over the Indian mainland, hot northwesterly winds from the desert are penetrating deep into the country," said Mahesh Palawat, Vice President of Meteorology and Climate Change at Skymet Weather. "When the days are hot, and there are no pre-monsoon activities in the evening, these high temperatures are reflected in higher nighttime temperatures as well."

But meteorologists say this is no longer just a seasonal weather pattern. The background climate itself is changing.

Humidity is now making the heat feel far more oppressive. India's average relative humidity increased from 67.1 per cent during 2015-2019 to 71.2 per cent between 2020-2024. During the same period, compound hot-humid days - when high heat combines with elevated moisture levels - jumped from 14,086 to 16,970.

That shift may sound technical, but its effects are deeply physical. High humidity weakens the body's ability to cool itself through sweating, increasing the risk of heat exhaustion, dehydration, and heatstroke even when temperatures are not at record highs.

The states recording the highest number of compound hot-humid days include Uttar Pradesh, Tamil Nadu, Bihar, Gujarat, Odisha, West Bengal, Andhra Pradesh, Haryana, Rajasthan, and Madhya Pradesh - a sign that dangerous heat stress is spreading well beyond traditionally humid coastal belts.

Meanwhile, India's cities are increasingly acting like giant heat batteries.

Urban Heat Island (UHI) intensity across Indian cities now ranges between 2 and 10 degrees Celsius, according to research cited in the Climate Trends brief. Concrete, asphalt, glass buildings, reduced tree cover, vehicle emissions, and waste heat from air conditioners trap warmth during the day and slowly release it overnight, keeping cities significantly hotter than nearby rural areas.

The irony is difficult to ignore: the more cities depend on cooling systems to survive extreme heat, the more excess heat they generate.

"India's heatwaves are no longer being driven by temperature alone," said Aarti Khosla, Founder and Director of Climate Trends. "What we are witnessing today is a dangerous convergence of rising temperatures, warmer nights, increasing humidity, and rapid urbanisation, all of which are amplifying heat stress across the country."

Climate scientists say another invisible factor is worsening the crisis beneath the surface - dry soil.

When soils lose moisture, less solar energy is used for evaporation, and more is converted directly into heating the air above. Researchers studying north-central India have found that unusually dry soil conditions weeks before a heatwave can intensify extreme temperatures and create feedback loops that prolong hot spells.

This year's drier winter and reduced Himalayan snowfall may also be playing a role.

Raghu Murtugudde, Emeritus Professor of Atmospheric and Oceanic Science and Earth System Science at the University of Maryland and visiting professor at IIT Kanpur, said warming in high-altitude regions is accelerating due to shrinking snow cover and ice-albedo feedbacks.

"Warm atmosphere is thirsty, so it holds more moisture. Water vapour is a powerful greenhouse gas, so that adds to accelerating warming," he said. "Urbanisation and deforestation are also adding to this mess."

The broader climate signal is unmistakable.

A recent ClimaMeter analysis found that India's deadly April 2026 heatwave unfolded in conditions that were up to 2 degrees Celsius warmer than similar events in previous decades because of human-caused climate change. The study estimated that nearly 44 million people and $341 billion worth of economic activity were exposed to intensified heat risks during the event.

Researchers concluded that natural climate variability played only a secondary role. The primary driver was the long-term warming caused by fossil fuel emissions.

The economic consequences are already becoming visible. Electricity demand is surging to record highs as air conditioner use rises. Health systems in several cities have reported spikes in heat-related illnesses. Agricultural productivity is under pressure as delayed rainfall and rising temperatures damage crops and dry out soils.

Experts say India's challenge is no longer simply about surviving summer. It is about adapting to a future where heat becomes chronic.

At the India Heat Summit 2026, organised by Climate Trends, Dr Ajay Mathur of IIT Delhi warned that heat is now a systemic national issue affecting infrastructure, agriculture, power demand, public health, and urban planning simultaneously.

"We need budget heads in the centre and states on heat management," he said. "We need a national heat resilience framework that integrates IMD warnings with municipal action plans."

Because the most alarming part of India's heat story may not be the 48 degrees Celsius afternoons making headlines.

It is a fact that even after midnight, the country is no longer cooling down.