Most households can record up to 7 mnths of heat exposure: Study

A study reveals low-income households in Chennai face severe nighttime heat stress, with indoor temps exceeding 31°C, stressing the need for improved housing policies.

Households — particularly in low- and middle-income groups are highly prone to night-time thermal heat stress, with indoor temperatures frequently exceeding 32°C, equivalent to 5,700 and 5,800 hours (equivalent to eight months) in the worst impacted households. In most households, it was exceeding this between 3,000 and 5,000 hours of continuous heat, a new study has found.

The study, released by the research organisation Climate Trends as part of the India Heat Summit 2026 in Delhi on Wednesday, was carried out across 50 low and middle-income houses in Chennai, between October 2025 and April 2026. (Chandet - stock.adobe.com)

The study, released by the research organisation Climate Trends as part of the India Heat Summit 2026 in Delhi on Wednesday, was carried out across 50 low and middle-income houses in Chennai, between October 2025 and April 2026 using high-resolution sensor data. It found that temperatures peaked between 8 and 9pm at around35°C and nighttime temperatures (between 8pm - 6am) rarely fell below 31°C even during the cooler months of the study period, flagging the impact is much worse during peak summer months.

“The large majority of households recorded between 3,000 and 5,000 hours, translating to four to seven months of persistent exposure,” said the study, titled ‘Nighttime Thermal Stress in Low and Middle Income Housing in India: Linking Indoor Temperatures and Relative Humidity with Perceptions of Comfort’.

The study’s most significant policy-relevant finding was that indoor heat exposure is determined by the structural characteristics of housing like construction materials, ventilation, and housing density. Across the 50 households, nearly all had concrete roofs with similar thermal mass properties.

“This delayed peak suggests significant heat retention caused by the building materials, which continue to release stored heat well after sunset,” said the study.

While every high income household in the sample had an air conditioner, every low income household had only a ceiling fan. “The cooling gap is binary: thermal comfort is achievable for those who can afford mechanical cooling. For those who cannot, heat exposure persists through the night,” it flags. India currently has over 300 Heat Action Plans, with 100 more in development. None of these mandate indoor temperature monitoring.

Aarti Khosla, founder and director, Climate Trends, said the study brings into focus how nighttime heat retention must also receive attention. “It is concerning to note the level of baseline heat exposure and heat stress for the residents, and what’s most pertinent is that even at night, their indoor temperatures rarely dropped below 31°C. Chennai’s high outdoor temperatures and relative humidity already pose difficult conditions. That its residents must also face chronic heat exposure indoors, and have it affect their sleep and recovery periods, is a matter that seeks urgent interventions,” she said.

The Summit, which consisted of over 200 researchers, scientists and government officials, was held in partnership with the National Disaster Management Authority (NDMA), Indian Meteorological Department (IMD), National Human Rights Commission (NHRC), Coalition for Disaster Resilient Infrastructure (CDRI), National Solar Energy Federation of India (NSEFI), and AuctusESG.

Speaking virtually at the Summit, Pralhad Joshi, Union Minister for New and Renewable Energy, acknowledged that rising temperatures and extreme weather events are realities affecting India’s cities, villages, economies. They are also impacting the daily lives of our citizens. Heat stress has emerged as one of the defining challenges of our times.”

Krishna Vatsa, HoD and member, NDMA, called for the need to revise building codes, keeping heat stress in mind.

“Building codes, even now, are not being applied uniformally and those working on the building code have access to cooling. Meanwhile, a change to the building codes, will actually make a difference to those who do not have access to cooling solutions, like informal structures. A certain amount of focus needs to go around providing thermal comfort,” he said, calling for funds to be pooled beyond disaster relief funds.

IMD’s DG, Mrutyunjay Mohapatra, meanwhile stressed on the need for last mile communication – to rickshaw pullers, street vendors and domestic workers among others. “We organise mechanisms so that they get the forecast. But our warnings are mostly reaching and being seen by men and not women. We need to be more inclusive in dissemination.”

Raina Singh, Lead Specialist, Capacity Development, CDRI, meanwhile called for changes in the way buildings and houses are planned.

“A big focus has to be on infrastructure and how it can absorb and respond to heat. We also have to see, if infrastructurally, our hospitals are able to withstand heat. Similarly, critical power infrastructure, while they focus on meeting additional power demands, but are these assets safe from high heat and additional wear and tear? These are the kind of issues we need to look at,” she said.