Is the Urban Heat Island (UHI) Effect Making India So Hot?

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Is the Urban Heat Island (UHI) Effect Making India So Hot?

Kshama Gupta Kshama Gupta June 3, 2024 967 Views

Kshama Gupta and Kakali Deka

An international study highlights the significant role of climate change in the record-breaking heatwave affecting Asia, including India. India is facing early and severe heatwaves for the third consecutive summer, with temperatures already reaching 48°C in many Indian States and expected to hit 50°C. The India Meteorological Department (IMD) reports that 2022 was the fifth warmest year since 1901, with an annual mean temperature 0.51°C above the 1981-2010 average. A report published in 2023 by M. Rajeevan indicates that heatwaves are most prevalent in coastal Andhra Pradesh and central and northwestern India, with more heatwave days during El Niño years. The frequency of heatwaves in India increased by nearly 2.5 days from 1961 to 2021, and is expected to rise by 12 to 18 days due to climate change.

Urban Heat Island (UHI) effect exacerbates the situation, particularly in cities where urbanization leads to higher temperatures than surrounding areas. Factors contributing to UHI include reduced tree cover, dense buildings, heat-absorbing materials, and air pollution. Urban population is more vulnerable to impact of heat waves due to pre-existing condition of UHI i.e. already higher temperature in urban areas and the higher density of people living in small land area. Numerous characteristics of cities contribute to the formation of urban heat islands. First, less tree cover means less evapotranspiration, which reduces cooling. Second, buildings’ geometric features—especially those of tall ones—provide many surfaces for sunlight absorption and reflection. Closely spaced tall structures also impede wind and air passage, which lessens convectional cooling. The street canyon or urban canyon effect is influenced by several elements. Third, urban areas absorb more heat than rural ones due to the dark surfaces and thermal bulk qualities of prevalent metropolitan materials like concrete and asphalt. Urban heat islands and rural areas frequently have different nighttime temperatures than during the day. Fourth, the effect is exacerbated by air pollution and anthropogenic heat generation. The urban heat island effect is largely exacerbated by high concentrations of air pollution, especially greenhouse gases like carbon dioxide and ozone. Several researchers have studied UHI effect in different Indian cities to understand the implications of Urban Cover Change on the increasing urban temperature. In 32 cities around the nation, Study by K. Veena et al. (2020) and Rao P. et al. (2021) show significant increases in urban temperatures and heatwaves, particularly in the Indo-Gangetic Plains, largely due to land cover changes from non-built to built-up areas. This intensifies health risks for urban residents, especially in impoverished areas, leading to heat-related illnesses and fatalities. In an additional study, Rao P. et al. (2021) examined the spatiotemporal effects of heat wave hazards in the Indo-Gangetic Plains and discovered that there were more heat waves in the decade between 2010 and 2019 than in any other decade. The area affected by intense heat also consistently increased during this time. One of the main causes of this growth is the conversion of land cover from non-built up regions to built-up regions. This causes the urban heat island effect to become more constant and noticeable. The health and well-being of city dwellers is one of the main effects of urban heat islands. The majority of large Indian cities experience heat waves every summer, which disproportionately affect people living in impoverished regions and can result in heat fatigue, fainting, heat strokes, and even fatalities.

To mitigate urban heating in Indian cities, several strategies are recommended:

  1. High-Albedo Roofing: Using light-colored roofing materials with high reflectivity (albedo > 0.60) can significantly reduce heat absorption, potentially lowering roof temperatures by up to 25°C compared to darker materials.
  2. Reflective and Pervious Pavements: Reflective concrete and high-albedo pavements reduce heat, while pervious pavements promote water infiltration, cooling the surface through evapotranspiration.
  3. Green Roofing: Implementing green roofs, which typically cover 21-26% of urban areas, helps lower surface temperatures, extends runoff duration, and reduces energy consumption, thereby improving the energy balance of buildings.
  4. Blue-Green Infrastructure (BGI): Creating a network of natural and semi-natural elements, such as wetlands, parks, green roofs, and water bodies, helps regulate city temperatures. An 8% increase in BGI area in Singapore reduced temperatures by 1.21°C. Rejuvenating a single water body in an Indian city stabilized its temperature, indicating that a comprehensive BGI network could significantly impact urban temperature reduction and mitigate global warming and heat waves.

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