Imperial College London

Climate change made deadly heatwave in India and Pakistan 30 times more likely

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Indians brave the heat wave at the bank of Sangam, the confluence of Holy river Ganges , Yamuna and mythical Saraswati during the hot summer day in Prayagraj, India

Indians brave the heat wave at the bank of Sangam during a hot summer day in Prayagraj, India.

Climate attribution science links human-caused climate change and a recent devastating spring heatwave in India and Pakistan.

March 2022 was the hottest month in India since records began 122 years ago. Pakistan also saw record temperatures, with the heatwave intensifying in both countries in April. The prolonged heat has caused widespread human suffering, and at least 90 people have died.

"In this part of the world, heatwaves are particularly hazardous to the 60% of the population who work outdoors and are therefore limited in their means to cope." Dr Mariam Zachariah

A new analysis carried out by an international team of leading climate scientists has found that the heatwave was about 30 times more likely because of human-caused climate change. 

The study is the latest 'rapid analysis' of an extreme weather event using climate attribution science, and was co-led by Dr Mariam Zachariah and Dr Friederike (Fredi) Otto from the Grantham Institute – Climate Change and the Environment at Imperial College London.

"In this part of the world, heatwaves are particularly hazardous to the 60% of the population who work outdoors and are therefore limited in their means to cope," said lead author Dr Zachariah (pictured below).

Headshot of Dr Mariam ZachariahMarch was also extremely dry, with rain shortfalls of 62% and 71% below the long-term average for this month in Pakistan and India, respectively. The unusually early heatwave, combined with the lack of rain, has led to wheat crop failures, as well as power outages due to unprecedented energy demand for cooling, and forest fires.

"Learning from previous years, India has been remarkable in rolling out Heat Action Plans, which now cover 130 cities and towns, and may have reduced the impacts in terms of direct heat-related deaths this year," adds Dr Zachariah. "However, initial reports of damage to wheat crops in the affected regions suggest the need for long-term strategies and preparedness in the event of future heatwaves." 

Quantifying the effect of climate change

To quantify the effect of climate change on the continued high temperatures in India and Pakistan, Dr Otto, Dr Zachariah and their colleagues from the World Weather Attribution group analysed weather data and computer simulations to compare the climate as it is today, after about 1.2°C of global warming, with the climate of the past, following peer-reviewed methods. 

The analysis focused on the average maximum daily temperatures during March and April in north-western India and south-eastern Pakistan, the regions that were most severely affected.

"In countries where we have the data, heatwaves are the deadliest extreme weather events. As long as greenhouse gas emissions continue, events like these will become an increasingly common disaster." Dr Friederike Otto

The results showed that an event like the recent heatwave is still rare, with a 1% chance of happening each year. However, climate change caused by greenhouse gases from burning fossil fuels has made it about 30 times more likely to happen. This means that it would have been an extraordinarily rare event without the effects of human-caused climate change.

The study also shows that, if average global temperature rise reaches 2°C, such heatwaves would be expected as often as once every five years. Notably, the results of this study may be conservative estimates for the frequency of such events, due to a lack of long-term climate data for the India and Pakistan region.

"In countries where we have the data, heatwaves are the deadliest extreme weather events," said Dr Otto, head of World Weather Attribution and Senior Lecturer at the Grantham Institute. "At the same time, they are the type of extremes most strongly increasing in a warming world. As long as greenhouse gas emissions continue, events like these will become an increasingly common disaster."

Other recent studies by the World Weather Attribution initiative have highlighted the role of human-induced climate change in the extreme rainfall in the Southeast Africa storms and the South African floods earlier this year, and the damage caused by Japan’s Typhoon Hagibis in 2019.


Download the full study: Climate Change made devastating early heat in India and Pakistan 30 times more likely (43 pages, 1.7 MB)

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Lottie Butler

Lottie Butler
The Grantham Institute for Climate Change

Siobhan Stack-Maddox

Siobhan Stack-Maddox
Human Resources Division

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