Chennai's nights are no longer offering relief from the heat, even during non-summer months. A new study by Climate Trends found that indoor temperatures in low- and middle-income homes frequently crossed 32°C, with some households experiencing nearly eight months — up to 5,800 hours — of continuous heat exposure. Night temperatures rarely fell below 31°C.
Study Highlights Nighttime Thermal Stress
The study, titled Nighttime Thermal Stress in Low and Middle Income Housing in India, found that indoor spaces often became hottest between 8pm and 9pm, reaching nearly 34.7°C, as reinforced concrete buildings released heat absorbed during the day. Temperatures remained above 34°C well into the night, while humidity levels consistently stayed above 75%.
Researchers came up with the findings after monitoring temperature and humidity levels in 50 households between October 2025 and April 2026.
Expert Concerns on Baseline Heat Exposure
"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," said Aarti Khosla, founder and director of Climate Trends.
The study found the problem was linked more to housing structure than income. Reinforced cement concrete roofs and walls trapped heat, while dense urban layouts and poor ventilation reduced nighttime cooling.
Sharp Divide in Access to Cooling
Researchers also found a sharp divide in access to cooling. Every high-income household surveyed had ACs, while low-income households depended only on ceiling fans. "Thermal comfort is achievable for those who can afford mechanical cooling. For those who cannot, heat exposure persists through the night," the report said.
Heat Action Plans Overlook Indoor Exposure
The report warned that existing heat action plans focus largely on outdoor temperatures and daytime heat waves, overlooking indoor exposure where people spend most of their time. "Most people spend the majority of their time indoors, where they face the dual threats of heat stress and poor air quality. These exposures carry uncertain physiological trade-offs and add psychological as well as economic strain on individuals," said Naveen Puttaswamy, associate professor at Sri Ramachandra Institute of Higher Education and Research and co-author of the study.
Recommendations for Mitigation
The study recommended cool roofs, reflective coatings, improved cross-ventilation, climate-responsive building materials and mandatory indoor heat monitoring in urban heat action plans.
