Registered with the Registrar of Newspapers for India under R.N.I 53640/91
Vol. XXXIV No. 6, July 1-15, 2024
Study underlines need for city to tackle the Urban Heat Island Effect
-- by Varsha V.
A change in Chennai’s land-use pattern is driving the Urban Heat Island (UHI) effect, says a study Urbanisation Impacts on Heat Island Intensification: Cooling Strategies for Coastal Cities by the Center of Climate Change and Disaster Management at Anna University. Urban Heat Islands (UHIs) emerge when a city experiences temperatures much higher than its rural surroundings due to its relative inability to dissipate heat.
The reasons are multifold and arise largely from the impact of changed landscapes. Urban surfaces like concrete and tar absorb more heat than natural surfaces as they reflect lesser sunlight; they release the heat at night, causing a spike in temperature. The design of a city has its own impact, too – tall buildings are said to create an ‘urban canyon effect’ that blocks wind flow and traps heat near the surface. Of course, activities that generate heat and pollutionexacerbate matters as well – emissions from cars, for instance, and industrial emissions generate waste heat and contribute towards the greenhouse effect wherein greater water vapour or pollutants in the atmosphere trap and amplify heat. This creates a vicious cycle – hotter the climate, greater the demand for energy-intensive cooling; greater the use of such cooling, greater the generation of waste heat, and so on. According to the study from Anna University, Chennai has seen an increase in residential, commercial and industrial areas (reportedly 48.7 per cent in 2017 against 17.7 per cent in 1988) accompanied by a decrease in agricultural lands (19.6 per cent in 2017 against 42.4 per cent in 1988) and forest land. Land surface temperature (LST) studies conducted by the GCC show a rising trend in minimum and maximum values over the years – the recorded numbers were 27.12 degree C and 36.62 degree C in 2018; 26.73 and 40.75 in 2020; and 31.66 and 43.45 in 2022 (source: Impact of Urban Vegetation Loss on Urban Heat Islands: A Case Study of Chennai Metropolitan Area, published in the Indian Journal of Science and Technology, Jan 2024.) It is notable that some areas in the city are observed to be significantly hotter than others – particularly, built-up neighbourhoods with fewer green spaces and water bodies.
Many of the measures to tackle UHIs fall squarely in the domain of civic planning; whether it is the planned increase in urban greenery and open spaces, or the design of wind corridors and energy-efficient neighbourhoods, there is no single entity with greater power to build a heat-resilient city than the civic administration. Singapore’s efforts, for instance, are highlighted on the World Bank blog and the three most notable action points all fall under the city administration – (a) the nurturing of urban greenery such that every residence is within a ten-minute walk to a park by 2030; (b) the incentivising of greenery in new developments, especially ‘skyrise greening’ or the creation of vertical greenery that lessens cooling load; and (c) the use of innovative building materials such as cool paints. Closer home, states like Punjab offer incentives for green buildings such as discounts on FSIs; and last year, efforts to assuage heat-stressed parts of Mumbai saw the Brihanmumbai Municipal Corporation and Marol Co-op Industrial Estate initiate the development of a 3.2 acre urban forest and nature conservancy park to increase green cover.
To its credit, Tamil Nadu has been quite proactive in its efforts towards the cause. It was just last year in June that the State Government launched the city’s first Climate Action Plan (CAP) in alignment with the Paris Agreement, an international treaty on climate change. The six areas of priority identified in the CAP – electrical grid and renewable energy, building energy, sustainable transport, solid waste management, urban flooding and water scarcity, vulnerable populations and health – are all significant in their direct and indirect potential to mitigate the UHI effect. With the goal to adopt an integrated approach to land use and infrastructure planning, the Third Master plan will embed key actions from the Chennai CAP. In a quote to The Hindu referring to the city’s plans to mitigate the rising heat, Anshul Mishra, Member Secretary, CMDA said, “Sustainable urban growth is possible. A two-pronged approach – compaction of core city and developing the satellite towns around growth centres or existing small towns – has been taken up by the CMDA, apart from undertaking 26 studies for preparing the Third Master Plan.” If successful, Chennai stands to demonstrate that able civic planning can significantly soften the brunt of climate change.
