CSE Report Warns Urban Heat Islands Raising Night Temperatures by Up to 15 Degrees Celsius

Rising temperatures and expanding urban infrastructure are creating localised “heat pockets” in many Indian cities, a phenomenon experts warn could significantly strain cardiovascular health. As India moves toward the peak summer months, forecasts from the India Meteorological Department indicate that temperatures are likely to remain hotter than usual through May. Researchers say the problem is not only the heat from the sun but also the way modern cities trap and retain warmth, creating conditions that increase health risks for residents.

These localised heat pockets are closely linked to the broader urban heat island effect, where built-up areas experience higher temperatures than surrounding rural regions. Concrete, asphalt, and dense infrastructure absorb heat during the day and release it slowly at night, preventing cities from cooling down. According to studies cited in the journal Environmental Science & Technology, this persistent warmth increases mortality risks during heatwaves, highlighting a growing public health concern in rapidly urbanising regions.

Recent satellite observations and a 2026 report from the Centre for Science and Environment indicate that even cities with improved green cover, such as Bengaluru and Hyderabad, are experiencing significant increases in land surface temperatures. In some locations, surface temperatures have risen between 7°C and 15°C over the past few decades due to expanding “grey infrastructure". When heat stored in buildings and roads is released overnight, nighttime temperatures remain elevated, reducing the body’s natural recovery period from daytime heat exposure.

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Health experts say this persistent heat places additional stress on the heart as the body attempts to regulate internal temperature. High humidity and extreme temperatures—sometimes described as “moist heatwaves”—make sweating less effective because moisture cannot evaporate efficiently from the skin. According to the World Health Organization, this can cause heart rates to rise sharply as the body struggles to cool itself, increasing the risk of heat exhaustion, dehydration, and even acute cardiac complications in vulnerable individuals.

Urban density further intensifies the problem. Areas with limited green spaces, narrow streets, and extensive air-conditioning use often experience significantly higher temperatures than nearby neighbourhoods with trees and water bodies. A 2025 study by the Council on Energy, Environment and Water found that nearly 60 per cent of Indian districts face high risk from extreme heat events. Waste heat from air conditioners and the lack of “blue-green” infrastructure—such as lakes, parks, and urban forests—can create heat traps in densely populated localities.

Experts suggest that both urban planning reforms and personal precautions are necessary to reduce health risks. Measures such as reflective “cool roof” coatings, improved ventilation, increased tree cover, and avoiding strenuous outdoor activity during peak afternoon hours can help mitigate heat exposure. As extreme heat events become more frequent, public health researchers stress that managing urban heat will require coordinated action by city planners, health authorities, and residents to prevent a growing climate-related health crisis.

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