Winter nights in city warmer in past 20yrs
The city is bracing itself for a few months of warm summer nights. But the winter nights were no better.
An analysis by the India Meteorological Department (IMD) showed the frequency of warm nights in Mumbai during winter has almost doubled in the past two decades because of the growth of high-rise structures, more vehicles on the roads and fewer open spaces.
The study was done by IMD and University of Wester n Ontario, Canada, on urban heat islands from November to February. An urban heat island is an area significantly warmer than its surroundings because of human activity.
The analysis found t hat between 1969 and 2009, during the sunset hour, the temperature difference between the Colaba and Santacruz weather stations was only 0.5 degree Celsius . This distinction, however, grew as the night progressed. The hourly temperature recorded at Colaba was 3 to 4 degrees Celsius more than at Santacruz.
“The urban heat island phenomenon in metros is because of rapid urbanisation and modern building structures that retain more heat,” said AK Srivastava, the lead investigator, IMD. “Heat islands are more prominent during winter nights, a trend seen in cities across the world.”
The study analysed how often such heat island events took place in Mumbai over four decades. The decade between 1991 and 2000 recorded 98 nights — when the difference between hourly temperature at Colaba and Santacruz weather stations was more than 3 degrees Celsius for most hours after sunset. This is followed by 90 events from 2001-2009.
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