Win­ter nights in city warmer in past 20yrs

Hindustan Times ST (Mumbai) - HT Navi Mumbai Live - - FRONT PAGE - Sne­hal Re­bello sne­hal.re­bello@hin­dus­tan­times.com

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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