New Delhi: Climate change may have played a significant role in the heatwave that swept across north India and Pakistan in mid-April, according to scientists working with ClimaMeter, a collaborative of organisations and experts who analyse extreme weather events in the context of climate change.

According to their analysis of meteorological data from the 1950s to now, this April’s heatwave was a “very exceptional” meteorological event. It wasn’t affected by natural climate variability but was instead greatly shaped by climate change.

And more heatwaves are brewing in India as the summer progresses. As per a press statement by the India Meteorological Department on April 21, another heatwave will likely hit parts of central and north India from April 21 to 26.

Heatwave influenced by climate change

The India Meteorological Department defines heatwaves as periods of unusually high temperatures that occur in an area when compared to what is normally expected over the region during that time. While meteorological conditions – such as low wind speeds – can increase temperatures in an area, heatwaves have been tied to human activities as well.

For instance, the sixth assessment report of the Intergovernmental Panel on Climate Change (IPCC, a body under the United Nations that ) in 2021 concluded that human activities such as the burning of fossil fuels and the greenhouse gas emissions that these fuels emit have caused an increase in the frequencies and intensities of some climate events – including heatwaves – since pre-industrial times.

In this sense, heatwaves are classified as an extreme weather event caused by climate change.

India and Pakistan witnessed a heatwave in April this year. India experienced the heatwave rather early as the summer progressed: it set in by around April 8 and by April 11, and parts of northwest India including the capital city of Delhi recorded temperatures above 40 Degrees Celsius. The IMD issued red alerts for several areas. 

Scientists working with ClimaMeter, a collaborative of organisations and experts who analyse extreme weather events in the context of climate change, studied the meteorological conditions that led to the April heatwave.

Also Read: Heatwave Sets In Over Northwest India

The team accessed reanalysed satellite data (ERA5) to see how these meteorological conditions have changed in the present (from 1987 to 2023), when compared to the past (1950 to 1986). They found that based on similar events in the past, meteorological patterns associated with the heatwave, occur with a similar frequency now as they did in the past: surface or atmospheric pressure – a factor that influences weather greatly – did not show any significant changes, and neither did rainfall or wind speeds.

And yet, there were huge changes in temperature: the heatwave of April 14 and 15 was more than 4 Degrees Celsius warmer than it would have been in the past. The team also found that urban areas – such as New Delhi, Jaipur and Islamabad in Pakistan now experience warmer conditions. Islamabad was the most affected, and it witnessed temperatures of up to more than 3 Degrees Celsius higher than in the past.

However, natural climate variability – such as the El Niño and La Niña that are part of the phenomenon called the El Nino-Southern Oscillation (ENSO) – could affect temperatures too. For instance, El Niño years are often associated with warmer weather or heavier rainfall across the world. Across most of South Asia, for instance, an El Niño causes a normal to below normal southwest monsoon. 

But when the scientists analysed this possibility, they found that ENSO conditions played only a very small role in the April heatwave, because the area is currently undergoing an ENSO-neutral phase, the time when neither the El Niño and La Niña conditions are at work.

Their report, published on April 18, concludes therefore that the warmer temperatures during the India and Pakistan heatwave on April 14 and 15 can be mostly attributed to human-induced climate change. 

It must be noted, however, that this report is not yet peer-reviewed, though the methods it used are. Due to the paucity of data that was available for the analysis – given that the occurrence of such a heatwave is not just rare, but “very exceptional” – the scientists have also said that there is low confidence in the robustness of their methods:

“For this event we have low confidence in the robustness of our approach given the available climate data, as the event is very exceptional in the database.”

Another heatwave looms over central and north India

“The spring heatwave gripping India and Pakistan underscores an alarming intensification of climate extremes, profoundly affecting millions throughout the region,” Gianmarco Mengaldo, a scientist at the National University of Singapore said in a press statement.

“Indeed, the tropical Indo-Pacific region is witnessing a shift in weather patterns that are increasing the frequency of heatwaves…As temperatures approach thresholds that test human survivability, these extreme conditions underscore profound vulnerabilities in healthcare systems, food security, and essential infrastructure. This, in turn, necessitates immediate action and strengthened resilience to withstand future climate challenges.”

Meanwhile, another heatwave is brewing. According to the India Meteorological Department (IMD), parts of north and central India will likely experience heatwave conditions between April 21 and 26. In a press release on April 21, the IMD warned that isolated areas in east Rajasthan would likely experience heatwave conditions from April 21 to 26.

Parts of Madhya Pradesh, the Vidarbha region in Maharashtra, and Chhattisgarh could witness similar conditions April 21 to 25. Between April 22 and 25, Haryana and Odisha would likely experience heatwave conditions too, as will parts of Uttar Pradesh from April 22 to 26. Similarly, parts of Punjab and West Bengal and western Rajasthan too could witness heatwaves on some days between April 23 and 26. Bihar and Jharkhand, meanwhile, could experience heatwave conditions on April 25 and 26.

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