How to reduce the urban heat island effect - Hindustan Times
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How to reduce the urban heat island effect

ByJayanarayanan Kuttippurath and Sarath Raj
Jun 14, 2022 12:01 PM IST

Since many of our cities are not planned, their future expansion must be planned in accordance with the heat island scenario. The city expansion should not be at the expense of its water bodies and vegetated areas

Several parts of India are reeling under severe heatwaves, with cities facing the brunt due to tightly spaced and tall buildings, industries, fewer green areas, and other impermeable infrastructure that absorb the incoming solar radiation and then radiate it back to warm the atmosphere. This over-concretisation and lack of green cover lead to the creation of urban heat islands (UHIs). There are two types of UHIs – surface UHI and atmospheric UHI – based on the methods used to measure them and impacts.

Women use scarves to shield themselves from the heat on hot summer afternoon, New Delhi, June 8, 2022 (PTI)
Women use scarves to shield themselves from the heat on hot summer afternoon, New Delhi, June 8, 2022 (PTI)

As UHIs are associated with higher temperature, materials and the type of surface play an important role. For example:

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•More impermeable surfaces and reduced natural landscape in urban areas

•Materials used in urban constructions absorb and emit radiation more compared to natural surfaces.

•The layout of the urban area: The wind flow and ability of urban materials to absorb and emit heat is also governed by the compactness and size of the buildings.

•Anthropogenic heat emissions: Vehicles, air-conditioning units, buildings, and industrial facilities all emit heat into the urban environment.

•Geography and weather of the city.

•The climate crisis and global warming

The increased temperatures due to the formation of UHI affect the surrounding environment and quality of life. It also leads to increased demand for energy to cool buildings, higher emissions of pollutants and greenhouse gases, increased risk of heat-related illness and death, decreased thermal comfort levels and impaired water quality.

Climate Change and UHI

Global warming is the biggest threat that the environment faces these days. The global and India temperatures have been rising since the industrialisation, which is roughly about 1.06 degree from its pre-industrial average. Therefore, the background warming due to the climate crisis also plays a key role in UHI.

The warming would raise the temperature, and thus add more water vapour in the atmosphere. The moistened air would hold more temperature and again, drives additional warming by this positive feedback. In addition to this, climate oscillations such as El Nino and La Nina events affect the temperature in land regions.

For instance, the El Nino events usually lead to warm and dry conditions in India. The changes in Indian Ocean temperature have a great influence on Indian monsoon, which would also affect the moisture transport to the land regions.

More fire events, droughts, reduced or pattern changes in rainfall, changes in water bodies, and reduction in soil moisture are expected in the context of the climate crisis, which directly impacts the changes in temperature in the urban regions and thus, UHIs.

Heat islands and Public Health

Extreme heat events due to increasing temperatures can pose serious threat to human health. According to Intergovernmental Panel on Climate Change report titled “Climate Change 2022: Impacts, Adaptation and Vulnerability”, deaths related to circulatory, respiratory, diabetic and infectious diseases, as well as infant mortality are increased with high temperature. High-risk population, which includes older people, children, outdoor workers, and sick people are the most vulnerable to these events.

Natural disasters cause a large number of early deaths and heatwave-related deaths contribute most to this list in India. According to a recent study, death due to heat-related illness has increased from 3014 in 2001–05 to 5157 in 2011–15. This is a matter of serious concern since heatwave episodes are becoming more frequent in India.

How can we reduce UHI and its impact?

UHI mitigation efforts can also help in reducing the effects of the climate crisis. The reduction of heat islands implies lower temperature in urban areas, which in turn slackens the energy demand for cooling the buildings. This will reduce the electricity generation-related greenhouse gas emissions. These efforts can also improve the quality of living in cities.

Some of these strategies include:

•Increase the vegetation cover and green spaces in cities.

•Preserve or construct water bodies in urban areas, and harvest rain water.

•Using cool and high reflectivity materials in urban construction such as green roofs.

•Green-standard vehicles, fuels and industries

•Encourage the use of public transport

•Reduce atmospheric pollution and greenhouse gas emissions

•Plan smart cities that use innovative technology to enhance the living standard of its people

Since many of our cities are not planned, their future expansion must be planned in accordance with the heat island scenario. The city expansion should not be at the expense of its water bodies and vegetated areas. Studies should be conducted at the city level and then priority zones and sensitive areas should be marked. Future urban planning should include provisions for implementing effective strategies to mitigate heat islands and its detrimental effects. Dedicated research should be promoted for in-depth analysis of the effects of UHI and their drivers within individual cities.

Jayanarayanan Kuttippurath and Sarath Raj, are with the Centre for Oceans, Rivers, Atmosphere and Land Sciences (CORAL), Indian Institute of Technology Kharagpur

The views expressed are personal

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