DAYS ARE cooler in urban pockets compared to non-urban areas during summer, found researchers from the Indian Institute of Technology, Bombay. This runs contrary to the perception that cities are hotter during summer because of concrete structures packed together. The team that studied satellite data of 84 cities in India found that in interior India, particularly in Central India, the non-urban areas adjacent to cities saw hotter days during the peak of summer between March and May.
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The study, published in Scientific Reports of the Nature Publishing Group, also found that the temperatures in the non-urban areas had risen over the years owing to ‘unprecedented urbanisation’.
“During summer, there is very less vegetation in non-urban areas but in cities there are well-maintained gardens and lakes. Hence there is higher evapo-transpiration in urban areas, which drops the temperature,” said Subimal Ghosh, a co-author of the study and a professor of the Interdisciplinary Programme in Climate Studies of IIT-B.
The researchers have said that there is a need for better public health facilities to combat health hazards from heat waves in non-urban regions. “Usually more care is available at the urban areas as it is believed that they are hotter. However, the study proves otherwise highlighting the need for more care in non-urban areas,” said Ghosh.
They also noticed a temperature flip-flop in cities and surrounding non-urban areas in night and daytime temperatures across seasons. In summers, cities were cooler during the day compared to non-urban areas but the nights were hotter in cities. On the contrary, non-urban areas had cooler days during winters than cities but at night the temperature increased.
Ghosh said that rampant urbanisation that resulted in cutting down of trees in surrounding areas will adversely affect the temperature balance.
While the team has not studied the relation of global warming to the temperature balance phenomenon, it has studied the black carbon emissions in the 84 cities. The aerosols were a reason behind the warmer winter nights in non-urban areas.
“Larger aerosols emissions, released during biomass burning, etc, absorb the solar radiation and heat up the layer closest to land. This increases the temperature,” said Chandra Venkataraman, a coauthor and also a professor.