Human action causing mercury rise in urban centres, says study

EXPERTS SAY CHANGE IN LAND USE AND DECREASE IN GREEN COVER HAS LED TO THE HEAT ISLAND EFFECT, CAUSING A RISE IN TEMPERATURE IN CITIES

nKOLKATA:THE ‘heat island effect’ in the major Indian cities has shot up by at least one degree in the past 17 years due to land use changes and increase in anthropogenic pressures, says a new study published by researchers from the Indian Institute of Technology at Kharagpur.

The study was made public on Friday.

An urban heat island, or UHI, is a metropolitan area that experiences higher temperature than the rural areas surrounding it. The phenomenon of increasing heat island effect due to factors such as concrete buildings, vehicles, has been noticed in at least 44 Indian cities, each with a million plus population, during the period 2001 and 2017. The cities include Kolkata, Pune, Guwahati, Delhi and Jaipur.

“For the first time, we have found evidence of mean daytime Surface Urban Heat Island Intensity (SUHII) going up to two degrees Celsius for most cities, as analysed from satellite temperature measurements in monsoon and post-monsoon periods,” said Arun Chakraborty, associate professor at the Centre for Oceans, Rivers, Atmosphere and Land Sciences (CORALS) in IIT Kharagpur.

The SUHII is measured on the basis of difference in temperature between the main part of the cities and their outskirts. Chakraborty said this difference was around one degree Celsius before 2001.

The study titled ‘Anthropogenic forcing exacerbating the urban heat islands in India’ has been published in the international Elsevier publication Journal of Environmental Management. “The key finding in the study is the role of anthropogenic activities in increasing the urban temperature in India,” it said.

As per a World Bank report, approximately a third of the total population in India lived in cities in 2018. The trend shows an increase of urbanization by almost 4% in the last decade.

“To accommodate the additional needs of this increasing population, the cities have witnessed some of the major human activities pertaining to changes in land use and land cover through decrease in green cover and infrastructural development. In addition, Urban Heat Island situation demands more energy consumption that would trigger greenhouse gas emissions. These have led to modifying the temperature of a city,” said lead author of the paper Sarath Raj.

Researchers said the primary reasons behind this increasing heat island effect are blocking of air passages and wind channels by haphazard development and aerosols in the city’s air. These aerosols are acting like a blanket. At night, they don’t allow the heat to radiate. The heat gets trapped and accumulates, resulting in higher temperatures, the study said.