Urban heat islands are causing Indian cities to boil. And the poor are paying the price
The onset of summer occurred unexpectedly early in 2025. Alerts for heatwaves were being circulated by the India Meteorological Department by the end of March. The number of heatwave days in several Indian cities are expected to be much higher in 2025. The causes are significantly anthropogenic and well-known to all: lack of green spaces, disappearing water bodies, increasing pollution, surge in greenhouse gas emissions from vehicles and air conditioners, high density of informal settlements, and increased concrete surfaces causing the urban heat island (UHI) effect.
Days of extreme temperatures are most dreaded by families struggling to keep their homes cool. Low-income households are already battling heatwaves early in April, as observed during our on-ground surveys in the Sultanpuri settlement in northwest Delhi. In this densely packed neighbourhood with single-room tenements, children lack open spaces and parks to play, houses lack proper ventilation and cooling methods, open chulhas (traditional clay cookstoves) add to the heat and smoke, high density of houses resists the passage of hot air during nights, and a deficiency of trees causes a deficiency of shade in public spaces and over houses.
Cities that started out with 10-20 per cent green forest covers are now becoming concrete jungles; areas that were once gaons with highest forest covers in their states are now ‘LEED Platinum hubs’, without a single tree in sight. With increasing needs of urbanisation and development of newer smart cities, forests are being razed down to make space for concrete campuses. Trading tree covers for glass and concrete structures makes movement and functioning highly uncomfortable for those using such spaces during any time of the day during summers. Concrete jungles continue to intensify heat near ground through the UHI phenomenon, further adding to the woes of those needing to step out during peak hours or using public transport.
Extensive urbanisation has also reduced the water bodies in cities; lakes and wetlands are being filled in for construction, rivers are being polluted relentlessly. The cooling effect of these water bodies is now indeterminate, with heat absorbing surfaces replacing convective cooling surfaces. Disappearing lakes, wetlands, and water bodies deprive citizens of natural cooling sources and better micro-climates.
Effects of UHI include higher heat discomfort within houses, exacerbated air pollution levels affecting elderly and children adversely, and surge in energy consumption to keep houses cool. UHI is also associated with prolonged heatwaves and higher temperature anomalies. Heat retention during the day and release during the night leads to warmer areas in the city, thereby inhibiting natural cooling at night. This affects populations in low-income communities disproportionately, who may not have access to adequate resources for cooling. Consequently, increased heat stresses, especially at night, can lead to higher rates of heat stroke, heat-related illness, and mortality, as the body might not get a chance to recover from daytime heat.
A notable contrast in cities is the difference in heat in affluent neighbourhoods, compared to densely populated areas. While higher vegetation cover in low-density neighbourhoods keeps surface temperatures low, densely packed settlements bear the brunt of heatwaves severely. Air-conditioning from such neighbourhoods discharges heat that builds upon slum settlements and disrupts the city’s overall heat equilibrium. In addition to low vegetation, lacking view of the open sky (hindering heat escape through radiation), and lack of cooling techniques means that excessive heat becomes unbearable for the average residents, hindering daily activities and livelihoods. Expenditure on cooling equipment and surge in electricity bills compound their problems.
With increasing influx of population in urban areas, concretisation of reserved forests and green lands is expected to surge, indicating an increase in the UHI effect. A higher population leads to increased vehicular traffic on roads, also contributing to UHI and air pollution. Migrants living in metropolitan cities, rickshaw pullers, construction and factory workers, street vendors, delivery persons, domestic workers, and people working outdoors for most of the day bear the brunt of the peak hours of heat. Many of these are low- or average-income groups. Some may even be homeless, or street dwellers. These populations suffer maximum heat-related losses and health impacts.
Cooling informal settlements
How can heat risks for these communities be analysed? Non-profit SEEDS uses its one-of-its-kind artificial intelligence (AI) model to identify houses and buildings at risk. Supported by Microsoft, this AI model utilises live weather updates, contextual data, vegetation cover, UHIs, and proximity to water bodies to identify houses’ vulnerability to extreme heat. SEEDS has been instrumental in deploying this model in several settlements in Indian cities since 2022, thereby paving the way for numerous cooling interventions, health campaigns, and awareness workshops with communities and stakeholders.
For these low-income neighbourhoods, affordable and innovative interventions introduced by the SEEDS team, such as passive cooling techniques, cool roofs, using matkas (earthen vessels) on roofs, increasing reflectivity of building materials through reflective paints, introducing greenery, and cleaning up open spaces to allow convective release of heat at night has been able to moderate the heat absorption in informal settlements considerably, thereby also bringing down heat-related illnesses and fatalities. For these households, such additions and alterations can bring 5-6 degrees Celsius of difference, thereby making houses more comfortable and liveable. Introduction of water dispensers in these areas, heat shelters, and shaded spaces helps daily wage earners to take breaks during peak hours, thereby reducing the risk of heat strokes and loss in earnings.
As risk identification and assessment continue to assist in direct engagement with settlement dwellers and community leaders through awareness and interventions, the challenges also highlight the need for strategies and actionable solutions to combat UHI through urban planning, construction techniques, and infrastructural accessibility. Urban greening policies to expand the forest cover, promote green walls and roofs, and encourage blue-green infrastructure such as wetlands and water bodies can significantly reduce the heat absorption and boost the release of heat at night through evapotranspiration.
Strategies and policies that are inclusive and designed to address and mitigate disproportionate impacts of excessive heat on vulnerable populations play a key role in regaining cooler environs in informal settlements. Small-scale measures include provisions of heat shelters, shaded spaces, designating public buildings and government structures as cooling centres, ensuring access to drinking water in public places. Large-scale measures include encouraging reduced use of vehicles and increase in use of public transport, reducing anthropogenic heat production sources, shift to renewable sources of energy and access to healthcare infrastructure sufficiently equipped to manage heat-related illnesses and emergencies.
While it is useful to make interventions at various scales to mitigate the impacts of heatwaves and UHI, it is imperative to identify heatwaves as disasters, and develop heat action and mitigation plans, which are proactive rather than reactive. The onset of concrete jungles jeopardises the liveability of cities and needs to be matched with endurance of green jungles. This not only mitigates heat risks and global warming but also ensures the health and well-being of those who are most vulnerable and exposed to excessive heat.
Sumedha Dua is Project Manager, SEEDS
Views expressed are the author’s own and don’t necessarily reflect those of Down To Earth