50°C the new normal? Heat stress takes toll

New Delhi: With parts of Delhi seeing maximum temperatures in excess of 49 degrees Celsius (°C) on Sunday, two questions are uppermost on peoples’ minds: is 50 possible; and is the climate crisis behind this? The answers, according to experts, is that 50°C is indeed possible; and that the climate crisis is likely responsible for what is happening

New Delhi: With parts of Delhi seeing maximum temperatures in excess of 49 degrees Celsius (°C) on Sunday, two questions are uppermost on peoples’ minds: is 50 possible; and is the climate crisis behind this?

HT Image

The answers, according to experts, is that 50°C is indeed possible; and that the climate crisis is likely responsible for what is happening. In fact, it may be the new normal.

On Sunday, parts of Delhi recorded maximum temperatures over 49°C but many other parts of northwest India also burned. Banda in Uttar Pradesh recorded 49°C; Gurugram, Hisar and Narnaul in Haryana; and Khajuraho and Nowgong in Madhya Pradesh recorded maximum temperatures of over 47°C. And people should get used to these, suggested an expert.

“This is the new normal and it will remain so for years to come. Maximum temperatures during heatwave periods over northwest India have already gone up from 45-46°C to 47-48°C. With climate change, we are going to see three things with heatwaves: higher intensity; an increase in duration from, say, 5 days to 7-8 days at a stretch; and a larger impact area,” said M Rajeevan, former secretary, ministry of earth sciences.

The bad news: all three are already evident.

To be sure, there were exceptional events this year that contributed to the heatwave, but these could have still been caused by the climate crisis. Among these: a prolonged dry spell (northwest India and central India recorded 78% and 58% rainfall deficiency during the pre-monsoon season so far that started on March 1) ; and very few western disturbances that bring pre-monsoon rain to northwest India, resulting in clear skies and very high solar radiation.

“The atmospheric conditions were peculiar this year. There was an area of high pressure which formed in March and was centered around Gujarat. It persisted in April, leading to incursion of dry and hot northwesterlies inwards. There was an early spring as the westerly jet moved northward and led to a reduction in western disturbances that normally bring thunderstorms and some rain to the region. Clear skies due to lack of rains finally created conditions for an unprecedented heatwave spell. And in May, when severe cyclone Asani was weakening, it was also dragging northwesterly winds bringing hot, dry winds inward. Now again, hot northwesterlies are prevailing over the region. During La Nina years, we do not expect such heatwaves but this year is exceptional,” said DS Pai, director at the Institute of Climate Change Studies, government of Kerala and former IMD scientist.

La Nina, a cold current in the Pacific, is associated with relatively cooler summers in India.

Pai adds that he would term this year an “exception” but admits that “new areas” are now seeing these “high temperatures” and that “urbanisation creates pockets of extremely high temperatures”.

THE SCIENCE

The World Weather Attribution (WWA) network, a global collaboration of leading climate scientists who work on analysing whether a particular extreme weather event is linked to the climate crisis, will submit findings of their study on this year’s spring heatwave in India and Pakistan (in March and April) within the next fortnight.

WWA is expected to sum up how the climate crisis may have made such an unprecedented heatwave event possible. WWA scientists Sarah Kew and Robert Vautard said during a recent workshop that there is only a one in a 100 chance of such a heatwave occurring every year, stressing that the event was rare because of the very large area that was affected ; the long duration of the heatwave spell; and very early onset of the heatwave during the spring season. The scientists said the spell affected all of northwest India, central India and even parts of east India.

Vautard said even though the 2022 heatwave was unusual with return period of the order of 100 years, such events are occurring more often and its now alright to expect unbelievable extreme weather events.

“The temperatures that formerly constituted ‘extreme’ are now just unusual. And temperatures which were previously all but impossible are the new definition of extreme. Crucially, the change of likelihood happens fastest for the most extreme temperatures…an increase of 1ºC in global temperature therefore makes heatwaves more than 1ºC hotter,” WWA said in its guide released last week for journalists on ‘Reporting extreme weather and climate change.’

WWA cited an Intergovernmental Panel on Climate Change (IPCC) report from 2021 that said a heatwave that would have occurred once in 10 years in the pre-industrial climate will now occur 2.8 times over ten years and be 1.2°C hotter. At 2°C of global warming, it will occur 5.6 times and be 2.6°C hotter. Similarly, a heatwave that would have occurred once in 50 years in the pre-industrial climate will now occur 4.8 times over 50 years and be 1.2°C hotter. At 2°C of global warming, it will occur 13.9 times and be 2.7°C hotter.

URBANISATION

On Sunday, Mungeshpur and Najafgarh, both heavily built-up areas saw among the highest temperatures in Delhi. “There will be pockets in cities which record extremely high temperatures because of the urban heat island effect. Mungeshpur and Najafgarh are automatic weather stations and we do not have long-term data for these to see the climate change footprint. To understand climate change impacts, we should always see the data for Safdarjung and Palam stations which recorded 45°C to 46°C yesterday. Of course, the imprint of climate crisis on heatwave spells is obvious but let’s not discount the effect of urbanisation, population density etc,” said M Mohapatra, director general, IMD. Most experts believe both urbanisation and population density are factors that contribute to the climate crisis.

The high temperatures are in keeping with a 2020 Ministry of Earth Sciences report that expects the frequency, duration, intensity, and coverage of heatwaves over India to substantially increase in this century.