The phenomenon often seen in urban settings, known as the Urban Heat Island effect, has recently been the focus of much attention due to the severe heatwaves experienced across India. While rural areas typically exhibit lower temperatures, cities and densely populated locations are becoming increasingly hotter, a situation that experts attribute to variations in heating over highly urbanized and semi-urbanized areas and the availability of open green spaces.
Understanding Urban Heat Island
Urban Heat Island is a term that refers to specific areas within a city that retain more heat than the surrounding locality. This typically occurs due to the presence of concrete-made buildings and houses in cities that trap heat and prevent it from dissipating easily. The temperature difference can reach from 3 up to 5 degrees Celsius between these urban islands and the neighboring areas.
Why Cities are Hotter Than Rural Areas?
Studies have observed that localities with more green coverage, such as plants, trees, and forests, experience lower temperatures compared to areas devoid of vegetation. This natural cooling process is attributed to transpiration, a phenomena plants utilize to regulate temperature. Urbanization is, therefore, a primary factor contributing to the Urban Heat Island effect. The frequent construction of high-rise structures, roadways, parking lots, pavement, and public transportation lines accelerates this issue.
Factors Leading to Urban Heat Islands
Increased construction activities contribute significantly to the emergence of urban heat islands. Buildings and infrastructure require materials like asphalt and concrete that absorb large amounts of heat, thereby raising the mean surface temperature of urbanized areas. Additionally, many urban buildings have dark surfaces which decrease albedo and increase heat absorption. Overuse of air conditioning, which requires increased energy production and subsequently contributes to pollution, is also a factor. Other contributors include, urban architectures like tall buildings and narrow streets that obstruct air circulation thereby reducing natural cooling effects, and need for fossil fuels for transportation and lack of green spaces that would otherwise absorb carbon dioxide and reduce heat.
Decreasing Urban Heat Island Effect
Strategies to reduce the impact of urban heat islands include increasing green coverage in cities, thus reducing the overall heat load. Implementing passive cooling technology can provide natural ventilation. Other methodologies suggested by the IPCC report include adopting ancient Indian building designs, which have been known to use such technology, and could be adapted to modern facilities. Also, utilizing suitable construction materials, and encouraging rooftop and terrace gardens is important. Painting roofs and terraces with white or light colors that reflect heat can significantly reduce absorption and mitigate the effects.
NASA’s Perspective on India’s Urban Heat Islands
NASA has made observations regarding the prevalence of urban heat islands in India, especially Delhi. Data acquired from NASA’s Ecosystem Spaceborne Thermal Radiometer Experiment (Ecostress) shows higher temperatures in urban areas compared to rural locations. The data indicated greater incidences of urban heat islands as large red patches over Delhi and smaller patches around neighbouring cities such as Sonipat, Panipat, Jind, and Bhiwani. Ecostress, a radiometer-equipped device launched to the International Space Station in 2018, monitors plant temperatures alongside their water requirements and climatic influences.