Urbanisation of Tirunelveli city might warm it up

Study predicts emergence of ‘urban heat islands’ in city due to rapid urbanisation

Urban heat island effect might arise due to less vegetation and more built-up area.

This is one ten-year-challenge that city planners need to take note of: Tamil Nadu’s Tirunelveli city now has less vegetation and more urban areas, all in just one decade. This could create an ‘urban heat island’ — urban area that is significantly warmer than its surrounding rural areas — finds a study.

Green vegetation and water bodies are often lost as built-up areas in a city increase. Radiation from cemented floors, roads and buildings add to the temperature. This leads to a surge in surface and air temperatures, causing urban heat islands (UHIs) to form. According to Rajchandar Padmanaban, scientist at Portugal’s NOVA Information Management School, this is common in fast-growing cities in developing countries. Padmanaban and his colleagues including Avit Bhowmik (Royal Swedish Academy of Sciences, Sweden) investigated the environmental and climatological impacts of such unprecedented urbanisation in Tirunelveli, which has seen rapid population growth over the last two decades due to immigration of people.

To do this, the team fused satellite images of the city from multiple satellite sensors — a method usually used in remote sensing but rarely to model the emergence of urban heat islands. This however, gave them a higher accuracy in their results.

The team’s results, published in

PLOS ONE, show that the city has undergone rapid urbanisation (at an average rate of 4% between 2007 and 2017), with a 32% increase in the coverage of urban built-up area. Fertile cropland pastures (which show a decline of almost 60% in the city) have been converted to fallow lands (mostly real-estate plots, which have increased by a whopping 178%). Fallow lands have, in turn, been transformed into built-up areas. This was most prominent in the western riverine stretch of the city, where the Thamaraparani river flows by. Forested areas in the northeastern part decreased by 12% while the bush and shrubbery-covered infertile areas increased by 164% throughout the city.

The team’s land surface temperature assessments from the maps revealed a high potential for the emergence of UHIs in Tirunelveli. The highest areas at risk of this are the western riverine zone (which showed a loss of greenery) and eastern and southeastern Tirunelveli. The southeastern portion could be a potential UHI hotspot, the scientists add.

According to the authors, proper zonal planning that accommodates sufficient green spaces (such as urban greenery and water bodies) can prevent the emergence of more UHIs in future.

“Smart and energy-efficient construction materials and green roofs may also substantially help prevent the emergences of urban heat islands,” wrote Dr. Bhowmik in an email.