How Urban Heat Islands are turning Indian cities into death traps

As India’s cities bake under rising temperatures, the invisible threat of urban heat islands (UHIs) is turning homes into dangerous heat traps.

Urbanisation, concretisation, and loss of green cover are exacerbating health risks, leaving people wondering if governments are doing enough.

According to the Union Ministry of Health and Family Welfare, India recorded 360 heat-related deaths in 2024. However, non-profit Heat Watch reported 733 deaths, and a peer-reviewed Science Direct article estimated 1,116 deaths annually due to heatwaves.

Rising temperatures in cities

Cities like Delhi, Chennai, Hyderabad, and Mumbai are witnessing dangerous temperature spikes, highlighting the urgent need for sustainable urban planning and green infrastructure.

An urban heat island (UHI) is a phenomenon where urban areas experience higher temperatures than the rural areas close. This is primarily due to the increased presence of heat-absorbing materials like concrete and asphalt, reduced vegetation, and the release of waste heat from human activities.

Continuous exposure to higher temperatures in daily life can even kill you, experts say. With asphalt and concrete replacing trees, cities are heating up faster and longer.

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Delhi records temperatures between 39°C and 44.4°C. Hyderabad neighbourhoods report 40°C due to humidity and winds. Mumbai sees 34°C, and Chennai varies between 36°C and 40°C.

These figures paint a grim picture of India's urban future. "We are replacing the green cover which we had with asphalt and concrete now," architect G Kannan told The Federal, emphasising the direct link between unplanned construction and rising urban temperatures.

Causes of UHI effect

Three factors are primarily contributing to the UHI phenomenon. Firstly, building materials like asphalt and concrete retain heat. Secondly, cutting down trees eliminates natural cooling through evaporation and absorption.

Thirdly, "waste heat" from appliances like air conditioners, lights, and fans exacerbates the situation. "Waste heat is basically the heat that comes out of your appliances," Kannan explained, highlighting the role of everyday activities in heating our surroundings.

The impact is not just environmental—it affects health, equity, and how cities are designed and inhabited.

Chennai’s case study

A stark example is Chennai, where the built-up area surged from 30% in 2003 to 73% in 2023. Meanwhile, the green cover dwindled from 34% to just 20.3%. "We are occupying every bit of earth and not increasing green cover," a resident noted, lamenting the rapid concretisation.

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Temperatures above 41°C are considered dangerous to human health. Experts argue that more than climate change, it’s "unplanned urbanization that results in higher temperatures and even causes urban heat islands."

The Federal visited several parts of Chennai to document the harsh realities faced by residents struggling against intensifying heat.

Global solutions

Governments can mitigate heat stress by incentivising green infrastructure, much like solar adoption incentives. Singapore offers a model with vertical gardens, urban forests, and green pockets designed to fight UHIs.

"So there are a lot of green pockets...vertical gardening has been promoted, urban pockets, urban forests, Miyawaki forests," N Karthik, an urban planner, explained.

Tamil Nadu’s 2024 heat analysis report revealed that 74% of its population faces air temperatures above 35°C. Though the state has signed an MoU with the United Nations Environment Programme and started heat mapping, many Chennai residents say they have not yet felt any difference.

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