Hotter days: Heat stress to ‘intensify’ in 9 Indian cities including Delhi, Mumbai

Updated on Mar 30, 2017 07:38 PM IST

Delhi, Kolkata, Chennai and Ahmedabad are already heat-stressed, other cities likely to join the ranks in the coming years.

Delhi, Kolkata, Chennai and Ahmedabad are already heat-stressed; other cities likely to join the ranks in the coming years.(Diwakar Prasad/ HT Photo)
Delhi, Kolkata, Chennai and Ahmedabad are already heat-stressed; other cities likely to join the ranks in the coming years.(Diwakar Prasad/ HT Photo)
Hindustan Times | By, New Delhi

At least 9 major cities in India will witness intensifying heat stress even if 2015 Paris climate targets are reached and could experience extremely hot days every year in the future, a new study has said.

The study, published on Monday in the US journal Proceedings of the National Academy of Sciences, looked at 44 cities across the world. Kolkata, Bengaluru, Delhi, Mumbai, Chennai, Pune, Surat, Hyderabad and Ahmedabad were selected from India as they are the largest metropolitan areas and will continue to be this century.

The Paris Agreement seeks to limit the usage of fossil fuels in the world in the second half of the century, limiting the rise in average world temperatures to “well below” 2.0 degrees Celsius (3.6 Fahrenheit) above preindustrial times.

The study said at the global level, a warming of 1.5 degrees Celsius above the pre-industrial time will feed into heat stress that is 5-6 times worse than in the recent past (1979-2005) and 350 million people in these 44 megacities will face heat stress year after year.

It added Delhi, Kolkata, Chennai and Ahmedabad are already affected and that the West Bengal capital is the most heat-stressed among the 44 megacities across the world.

Heat stress broadly refers to the human body experiencing more heat than it can tolerate, and is calculated using the heat index that incorporates both air temperature and humidity conditions.

India faced a searing heat wave in 2015 that led to over 2000 deaths, and 2016 emerged as the hottest year since 1901. West Rajasthan, Gujarat and parts of Madhya Pradesh are already facing heat wave conditions.

Junior minister for science and technology and earth sciences, YS Chowdary, told the Lok Sabha this week that “the frequency of severe heat waves had increased sharply in the recent years.”

STATE 2013 2014 2015 2016
  Andhra Pradesh 1392 447 1422 100
  Telangana - - 584 300
  Odisha 1 24 - -
  West Bengal 4 19 - -
  Assam 12 - - -
  Jharakhand 6 - - -
  Maharashtra 3 36 - 43
  Madhya Pradesh 3 - 2 -
  Rajasthan 5 6 2 3
  Gujarat 3 3 7 87
  Chhattisgarh - 14 - -
  Kerala - - - 4
TOTAL 1433 549 2081 557
Source: Lok Sabha reply of Y.S. Chowdary, junior minister for science and technology on March 22, 2017.

Heat stress burden is greater in places with more people because the impact of the heat is larger and it is the “perfect storm,” Tom Matthews, a climatologist at Liverpool John Moores University in the United Kingdom who led the study, told Hindustan Times.

“The challenge posed by heat stress is likely to increase in the future because of two things: Rising air temperatures from global warming and population growth,” Matthews explained over instant messaging app Skype.

This is especially true for Kolkata, which will likely remain the most heat-stressed city for this whole century. Kolkata’s population could be 3 times higher by the end of the 21st century and even if global temperatures do not rise, heat stress would increase.

“Unfortunately, the climate will continue to warm, so both factors will drive up the heat stress challenge,” Matthews added.

If global average temperatures rise by 1.5 degrees Celsius, Mumbai will be added to the list of heat-stressed cities.

With a 2.7 degrees Celsius warming, that might be the result of the currently pledged targets for emissions reductions, both Hyderabad and Pune will become heat stressed. With 4 degrees warming Bengaluru will also enter the heat stressed zone.

Heat wave conditions usually form in India between March and June. Experts have listed increasing greenhouse gas emissions and the warming of the sea surfaces over the equatorial Indian and Pacific Oceans as possible factors.

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    Malavika Vyawahare tells science and environment stories using words, photos and multimedia. She studied environmental journalism at Columbia University and is based in Delhi.

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