The urban heat island effect

Rapid urbanisation increases temperatures

Published - December 19, 2017 12:15 am IST

Rapid and unplanned urbanisation of cities and concomitant reduction in vegetation results in increased rise in temperature compared to non-urban areas. To explain how this happens, a team of researchers from IIT-Bhubaneswar studied the warming of Bhubaneswar, a tier-2 city, due to rapid urbanisation compared to non-urban areas that surround it. The study was recently published in the journal Proceedings of the National Academy of Sciences , India Section A: Physical Sciences.

Rapid urbanisation combined with changes in land use pattern between 2000 and 2014 led to about 1.8°C warming of Bhubaneswar compared with surrounding non-urban areas (called the urban heat island effect), the researchers say. The team, which was led by Debadatta Swain from the School of Earth, Ocean and Climate Sciences at IIT-Bhubaneswar, found that increase in urbanisation has been rapid at 83% in the last 15 years. This has led to about 89% decrease in dense vegetation, about 2% decrease in water bodies and nearly 83% decrease in crop fields during the same period. Decrease in crop areas could either be due to urbanisation or fields remaining fallow. These changes have led to increase in the urban heat island effect. The central part of the city has not witnessed much change in land cover, while the adjoining areas have witnessed major changes due to expansion of the city, leading to the warming of the city.

“Bhubaneswar was once well covered by three forests. The 1999 Odisha super cyclone destroyed many trees, and many trees have been cut for road expansion. Today, only a very small percentage of forest cover is remaining,” says Debadatta Swain. All the losses mentioned negatively impact the thermal and radiative properties of the surface and make cities hotter than surrounding non-urban areas. With heavily built-up areas and concrete structures, most cities in India and in the world are warmer than surrounding non-urban areas due to the urban heat island effect. For instance, Delhi is 4-12°C warmer due to the urban heat island effect.

“With proper planning we can minimise the impacts. So urban dwellers may not suffer from excessive changes to heat and rainfall patterns,” says V. Vinoj, one of the co-authors of the paper.

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