Cities must learn to tackle heat

Most of the world’s population lives in urban and peri urban areas. About 31 per cent of India’s population lives in urban areas, and India’s urban population is expected to rise to around 814 million by 2050. Economic success in urban areas throughout India has led to migration from rural areas, but our cities continue to face significant challenges. Inadequate and expensive housing has pushed low-income p op ulations into informal settlements, while inefficient transport infrastructure, air pollution, and increasing vulnerability to climate-related disasters continue to lower the quality of urban life. Urban populations are increasingly vulnerable to climate-related hazards, intensified by ecological changes resulting from unsustainable infrastructure development, and growing inequality amongst urban residents.

One of the most critical climate-change related issues faced by cities is extreme heat. Heatwaves have become a serious public health threat in India. Cities around the world tend to be hotter than rural forested areas due to the Urban Heat Island Effect. Dense urban areas face the issue of urban heat island phenomenon. Areas with random planning and rapid construction have low natural vegetation, and lack in green cover, which causes heat to accumulate in certain pockets. Heat gets stored in the built environment of these spaces, and causes surface land temperatures to rise. Urban areas with unplanned growth are more prone to Urban Heat Island Effects (UHIE), as the increased use of manmade materials causes higher surface temperatures.

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In a city like Kolkata, urban areas are densely populated. Dense urban areas are highly vulnerable to UHI effect and growing frequency of heatwaves. Low and unstable income, as well as a particularity of the built environment restricts mitigation abilities of residents and puts them in a precarious position. With over 22 million inhabitants (Census 2011), Kolkata will only continue to grow. However, rising global temperatures will also make life in cities hotter. Lack of green cover, construction of concrete infrastructure, and lack of clean waterbodies exacerbate the problem. Kolkata is located between the fertile Indo-Gangetic plains and the vast Bay of Bengal, making it a very humid city.

Increasing heatwaves and high humidity makes summer in the city intolerable, and most people have limited ways of mitigating and adapting to rising temperatures. 2024 had the highest temperatures recorded, and this year has already witnessed some of the hottest days in April and May. The combination of hot and humid weather has heightened the vulnerability of inhabitants. Rising temperatures are associated with increased stress, fatigue, and heat-related illnesses, which in turn reduce productivity and contribute to income losses. As extreme heat intensifies, a growing number of people across the city will face constraints on outdoor activities.

As the climate changes, it is extremely necessary for people, as well as the government, to take active steps towards heat mitigation. Dealing with heat in Indian cities requires a two-pronged approach: one at the macro scale, and another that is locally specific and tailored to the unique challenges of each city. In the case of Kolkata, effective heat mitigation must respond not only to rising temperatures, but also to the city’s persistent humidity, dense urban fabric, and environmental vulnerabilities. At the broader institutional level, strategies such as urban greening, reducing air pollution, implementing co ol ro ofs, and improving climate-sensitive urban planning can significantly reduce urban heat exposure.

Expanding tree cover, preserving open spaces, and integrating heat-resilient infrastructure into urban development are essential interventions for Indian cities as a whole. For Kolkata specifically, institutional efforts must prioritize the protection and restoration of its wetlands, lakes, and other blue-green ecosystems which play a critical role in regulating urban temperatures and managing humidity. Increasing green spaces across dense neighbourhoods, alongside investments in innovative cooling infrastructure such as reflective and cool-roof technologies, can greatly help reduce heat stress for inhabitants of informal settlements. At the community and household level, heat management must be participatory, affordable, accessible, and grounded in local realities.

Small-scale interventions, when adopted collectively across neighbourhoods, can significantly improve thermal comfort and reduce localized heat stress. Simple activities such as building urban gardens in balconies, or on front yards, expands the green cover of the city and contributes to lower land surface temperatures in dense urban pockets. Beyond cooling, these gardens improve air quality, increase biodiversity, absorb rainwater, and provide relief in highly built-up environments. In a city like Kolkata, where open green space is often limited, household and community-led gardening can play an important role in creating microclimates that are cooler. Rooftop vegetable gardens and potted native plants can also strengthen residents’ connection to their local environment.

Similarly, planting large shade-giving trees in community spaces, streets, schools, and public gathering areas can provide long-term cooling benefits. Community-led stewardship of these trees encourages collective responsibility and creates shared shaded spaces that strengthen social cohesion while reducing exposure to extreme heat. Trees which have large canopies and are native to India, such as peepal, Mango, and Banyan reduce glare, and cool surrounding areas through evapotranspiration. Low-cost cooling measures at the household level can be highly effective. Techniques such as lime washing roofs, applying reflective coatings, installing bamboo or fabric shading, improving ventilation, and creating rooftop gardens can substantially lower indoor and roof surface temperatures.

These interventions are particularly important for low-income households that may not have access to air conditioning or other energy-intensive cooling systems. Lastly, adaptation to heat needs community action and institutional preparedness to work together. In cities like Ahmedabad, Delhi, and Hyderabad, programmes such as localized Heat Action Plans (HAPs) that integrate early warning systems, public awareness campaigns, community outreach led to better coordination between health, disaster management, and municipal agencies. This has significantly aided adaptation to rising temperatures and protection of vulnerable populations from heat stress.

Public communication on heat risks is essential. Policies promoting shaded rest areas, mandatory rest breaks, accessible drinking water, and hydration facilities for outdoor workers can help reduce heat-related illnesses and fatalities. The inevitability of climate-related disasters is now at our doorstep, and it is imperative for institutional bodies to place urban heat at the forefront of its concern. Community action, along with proactive measures by government, is critical to address heat risk in Kolkata.

(The writer is an Associate at the Cities Forum, where she collaborates with international development organizations, national governments, and private stakeholders to implement policy solutions to support inclusive climate adaptation.)