Urbanisation of Bhubaneswar, a tier-2 city in Odisha, India, has been rapid at 83% in the last 15 years (2000-2014) and this has led to about 89% decrease in dense vegetation and about 2% decrease in water bodies. This has led to about 1.8 degree C warming of the city compared with surrounding non-urban areas (urban heat island effect).
Rapid and unplanned urbanisation of cities and concomitant reduction in vegetation results in increased rise in temperature compared with surrounding non-urban areas. To explain how this happens, a team of researchers from the Indian Institute of Technology (IIT) Bhubaneswar, Jatni, studied the warming of Bhubaneswar, a tier-2 city, due to rapid urbanisation and compared it to surrounding non-urban areas.
Rapid urbanisation combined with changes in land use pattern between 2000 and 2014 led to about 1.8 degree C warming of the city compared with surrounding non-urban areas (urban heat island effect), says a study published recently in the journal Proceedings of the National Academy of Sciences, India Section A: Physical Sciences.
The team led by Dr. D. 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.
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 warming of the city.
“Bhubaneswar was once well covered by three forests. The 1999 Orissa 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 Dr. Swain.
Loss of vegetation, destruction of water bodies and increase in paved area negatively impacts thermal and radiative properties of surface making cities hotter than surrounding non-urban areas. With heavily built-up areas and concrete structures, most cities in India and globally are warmer than surrounding non-urban areas due to urban heat island effect. For instance, Delhi is 4-12 degree C warmer due to urban heat island effect.
“This study helped understand how rapid, unplanned growth of a city impacts the microclimate of the city. Even Bhubaneswar, which is only a tier-2 city, is witnessing an increase in temperature due to changes in land surface leading to urban heat island effect. With proper planning one can minimise the impacts so urban dwellers may not suffer from excessive changes to heat and rainfall patterns,” says Dr. V. Vinoj from the School of Earth, Ocean and Climate Sciences at IIT Bhubaneswar and one of the co-authors of the paper.
The researchers used the Moderate Resolution Imaging Spectroradiometer (MODIS) to extract land surface temperature and Landsat-7 and 8 satellite imageries to study changes in vegetation cover. Changes in the land cover reveal pronounced growth of the city in particular directions.