Battling urban heat islands in India

Temperatures in the Capital have surged to a record-breaking 52.3 degrees Celsius recently, according to the India Meteorological Department (IMD). This extreme heat was recorded in the Delhi suburb of Mungeshpur, marking the first time the temperature has breached the 50°C threshold in the history of the city. Over 300 lives have been lost due to heatwaves this summer across the country.

This alarming statistic underscores a growing issue: The urban heat island (UHI) effect, a phenomenon where urban areas experience significantly higher temperatures than their rural counterparts. The UHI effect is primarily driven by human activities and urbanisation, which replace natural landscapes with dense concentrations of buildings, roads, and other infrastructure. These materials, such as concrete and asphalt, absorb and retain heat more effectively than natural landscapes, causing urban temperatures to rise, particularly at night. In cities, buildings with dark surfaces have a lower albedo, meaning they reflect less sunlight and absorb more heat, exacerbating the temperature increase. The construction of closely built structures further compounds this issue by limiting airflow, creating pockets where heat becomes trapped and temperatures soar.

Green spaces play a crucial role in mitigating the UHI effect, yet many urban areas in India suffer from a lack of trees and plants. Vegetation provides natural cooling through shade and evapotranspiration, a process where plants release water vapour, which cools the air. Unfortunately, Indian cities often have poor tree density, with some areas having as few as one tree for every 450 people. This stark deficit not only exacerbates urban heating but also deprives residents of the numerous benefits that green spaces offer, including improved air quality and enhanced mental well-being.

The consequences of the UHI effect extend beyond mere discomfort. They pose serious health risks, particularly to vulnerable populations such as the elderly, infants, and those with pre-existing health conditions. Prolonged exposure to high temperatures can lead to heat-related illnesses, including heatstroke and dehydration, and in severe cases, it can be fatal. Moreover, the heat exacerbates air pollution levels, as higher temperatures contribute to the formation of ground-level ozone, a harmful pollutant. This combination of heat and pollution further strains public health systems and reduces the quality of life in urban areas.

Energy demand in cities also surges as temperatures rise, primarily due to increased use of air conditioning. This not only strains power grids but also leads to higher energy costs and increased greenhouse gas emissions.

Air conditioners themselves contribute to the UHI effect by releasing hot air into the environment, creating a vicious cycle where the need for cooling perpetuates the heating problem. According to a study by Resources for the Future, each 1°C increase in temperature raises energy demand by 0.5% to 5%, depending on the level of air conditioning penetration in the area. The environmental impacts of UHIs are significant as well. Higher urban temperatures contribute to global warming by increasing overall temperatures in and around cities. This warming effect can disrupt local ecosystems, harm wildlife, and reduce biodiversity. Additionally, the heat and associated pollution can degrade water quality in nearby streams and rivers, affecting aquatic life and further stressing urban ecosystems.

Addressing the UHI effect in India requires a multi-faceted approach. Increasing urban greenery is a fundamental step. Planting trees and creating green spaces can significantly reduce urban temperatures and provide numerous co-benefits. For instance, green roofs and vertical gardens can help cool buildings, reduce energy consumption, and improve air quality. The Indian Institute of Science suggests that an ideal tree-human ratio should be seven trees for every person, a stark contrast to the current reality in many cities. Urban planning and building design also need to prioritise heat mitigation. Using reflective and lighter-coloured materials for roofs and pavements can help reduce heat absorption. Implementing passive cooling techniques, such as natural ventilation and shading, can decrease the reliance on air conditioning. Innovations in building materials, like cool roofing materials and reflective paints, can play a critical role in reducing the UHI effect.

Technological advancements can enhance heat risk monitoring and management. For instance, deploying more weather stations in cities can provide high-resolution data on temperature variations, helping to identify and address UHI hotspots. The successful implementation of heat action plans, such as the one developed in Ahmedabad, can serve as a model for other cities. Ahmedabad’s plan, which includes temporary monitoring stations, satellite-based heat maps, and early warning systems, has significantly improved the ability of the city to manage extreme heat events and reduce heat-related mortality.

While urban heat islands and the climate crisis are related, they are distinct phenomena. Heat islands occur when cities are hotter than their surroundings due to urbanisation, while climate change refers to the long-term warming of the Earth caused by greenhouse gases. However, the UHI effect can exacerbate the impacts of the climate crisis, making cities more vulnerable to heatwaves and other extreme weather events.

The urban heat island effect is a pressing issue that requires immediate attention and action. As cities continue to grow and urbanise, the need for sustainable urban planning and green infrastructure becomes ever more critical.

By implementing a combination of greenery, innovative building materials, and advanced monitoring technologies, Indian cities can mitigate the UHI effect, protect public health, and enhance the overall quality of urban life. Addressing this issue is not just about reducing temperatures; it is about creating healthier, more resilient, and more sustainable cities for the future.

This article is authored by Fauzia Khan, Member of Parliament, Rajya Sabha and Kaviraj Singh, founder and managing director, Earthood.