Impact of Urban Heat Islands in India: Reimagining Architecture for a Better Future

Credit: Mumbai Coastal Forest Project

Introduction

An urban heat island (UHI) refers to the phenomenon where cities and other built up areas experience higher temperatures compared to the surrounding rural areas, particularly at night. One of the main causes for this phenomenon is increasing urbanisation, because of which vegetation is replaced by concrete structures like buildings and roads. These structures absorb more solar energy than vegetation and retain heat due to their thermal properties. These properties include high thermal mass, allowing these structures to store heat during the daytime and release it at night, making urban areas warmer.

 In India, UHIs pose a significant threat due to large scale development. As of 2023, more than 40% of the Indian population lives in cities. It is projected that by the year 2050, around 60% of Indians will live in Urban areas. A high volume of migration to urban areas has led to a rapid expansion of cities, which in turn has wiped out natural vegetation to meet infrastructural needs. Such growth, which is largely unplanned, contributes to the creation of UHIs. However, rapid urbanization and poor planning are not the only causes of UHIs. Current architectural preferences in India are not climate-conducive and, in turn, aid in the creation of UHIs.

Why is Indian Architecture not urban heat-friendly?

Modernization has transformed architectural preferences, favouring glass buildings and skyscrapers over traditional styles. These architectural styles, which were suitable for cold climates, were adopted in India without considering that they were not adaptable to its hot climate.

Due to rising land costs, there is pressure to expand floor space by eliminating thick walls and courtyards. Further, concrete buildings are often preferred as they use space efficiently and are simply easier to build, making them a viable option.

However, these concrete structures retain heat, making the indoors warmer. For example, houses in Delhi and other north Indian cities are often built with thin walls made of red burnt clay bricks and concrete roofs. These materials quickly absorb heat and transfer it to interiors, thereby raising the temperature. Construction of tall and closely packed buildings to accommodate growing population prevents air flow and obstructs heat dispersion. To maximize the use of spaces, flat-roofed flats are increasingly being built. However, these structures contribute to the UHI effect as they absorb more heat compared to sloped houses.

How can Indian cities mitigate the UHI?

The dangers of urban heat have become painfully visible in Indian cities. One such example is Ahmedabad. In the year 2010, a heat wave killed more than 1,300 people in the city, forcing state officials to take urgent steps. This led to the development of South Asia’s first Heat Action Plan (HAP). A HAP includes strategies/guidelines that can be implemented by hospitals, government officials, and citizens immediately when temperatures rise beyond human tolerance. As a part of this plan, simple measures have been implemented that can protect people from urban heat. These include painting tin-roofed households with reflective paint. Such paints reflect sunlight and prevent heat absorption on walls and roofs, thereby reducing indoor temperatures. Water sprinklers were also installed on bus stop roofs to provide local cooling. These small steps make city architecture more resilient against the increasing threat of urban heat without resorting to highly polluting, energy intensive like air conditioners.

Another initiative of making Indian architecture friendly to UHI was the cool roof policy by the Telangana government. In the socioeconomic report, the Telangana government acknowledged that the state experiences a tropical climate due to its location in a semi-arid region, making it vulnerable to the formation of UHIs. To reduce the impact of such heat, the government launched India’s first cool roof policy, whereby roofs are coated with materials that reflect sunlight into the atmosphere, keeping indoor air temperatures lower by as much as 2.1 to 4.3°C.  When less than 10% of Indian households have air conditioning, cool roofs provide a low-carbon cooling solution to cope with extreme heat, while mitigating the UHI effect.

Similarly, Delhi implemented low-cost, multi-layered roofs made from local materials like bamboo, jute, and cardboard to reduce the UHI effect. These roofs reduce heat absorption, which can lower the indoor temperatures by six degrees Celsius. While some cities have taken innovative steps to reduce the UHI effect, a long-term impact requires rethinking Indian architecture to make it UHI-friendly. This can be done by aligning Indian architecture with the country's climatic conditions and integrating traditional elements with modern architecture. This idea ensures alignment with global architecture while reducing the UHI effect.

Further poor urban planning, including pathways without proper shade, also contributes to the UHI effect. These concrete surfaces absorb heat and slowly release it, making the atmosphere around them warmer. This becomes worse when such structures are not surrounded by green vegetation, as plants aid in evaporation, thereby keeping the surroundings cool. For example, the lack of natural shade cover on the pathway of Marine Drive in Mumbai intensifies the UHI effect, making the area virtually unusable for most of the day. 

Strategic urban planning is important in addressing such heat-related challenges. In response to this heat stress, citizens have proposed creating a green urban forest along the Mumbai Coastal Road. The proposal aims to transform the reclaimed coastal land into a climate-smart green zone by planting local plants such as kewda, sultan champa, and others along the seaward belt. This initiative aims to serve as an ecological shield for Mumbai by maximising the cooling effect and reducing surface temperature near the Coastal Road, thereby mitigating UHI.

Rethinking the way to build Indian cities

To address the UHI impact, it is important to integrate sustainable and environmentally friendly practices in the architectural planning of homes and buildings in Indian cities. A small shift towards localized approaches can play a huge role in mitigating UHI effects. Some of these approaches are:

1. Using earthen walls and roofs in building homes: Earthen architecture utilizes natural materials, such as clay, which have thermal properties. These properties enable them to absorb less heat during the day, thereby keeping the indoor temperature low. Additionally, they emit less carbon as compared to concrete buildings, making them an eco-friendly material.

2. Incorporating perforated screens: These screens were traditionally used for keeping the buildings cooler than the outside. Its design enables hot air to rise from the upper part of the screen, while cool air is drawn in. This keeps the inner temperature low. Moreover, this panel covers the building, thereby preventing the walls from direct heat. The most significant example of this approach is the Hawa Mahal in Jaipur, Rajasthan.

3. Using projecting eaves:  Projecting eaves are projections used above windows or along the roof in homes.  These eaves extend out from the home, providing extra shade to windows and walls from direct sunlight. This helps in reducing the inner temperature within homes and buildings without relying on electrical gadgets like fans and air conditioners.

4. Adopting green roofs:  This involves covering the rooftop (completely or partially) with green vegetation over a waterproof membrane. This vegetation absorbs less heat and undergoes evaporation, hence keeping nearby surfaces cool. This idea can be adopted by making roof gardens on a terrace.

5. Developing tree-shaded pathways: Developing a green cover, including trees and canopies along pathways, lowers surface and ambient temperatures. Trees provide natural cooling to the surrounding areas by providing shade, thereby decreasing the amount of direct sunlight reaching the ground. Further, during evapotranspiration, plants release moisture, which cools the surrounding air.

Conclusion

When analysed closely, the issue of UHI in India highlights the ongoing conflict between modern architecture and environmental concerns. Modern Indian architecture has prioritized global architectural aesthetics, such as concrete buildings, over sustainable designs. This transition has intensified urban heat stress, thereby adversely impacting people’s lives. Cities like Ahmedabad depict a progressive approach towards integrating ecologically responsible practices in Indian architecture. However, it is essential to incorporate these practices into urban architecture policies for their effective implementation.

[This post has been authored by Shreya Maheshwari, a first-year law student at JGLS.]