Climate change aided April heatwave by 30 times

The heatwave that gripped parts of India, Bangladesh and other countries in South and Southeast Asia was made 30 times more likely by climate change, said a new study.

World Weather Attribution, an international collaborative research initiative, said climate change not only increased the frequency of the disaster but also its duration and intensity. As many as 23 researchers, including nine from India, were involved in the study.

Several northern and eastern parts of India recorded temperatures above 44 degrees C on April 18. Mumbai alone reported 13 fatalities and 650 hospitalisations. Parts of Bangladesh saw the highest maximum temperature recorded in decades at 40.6 degrees C. On the eastern part of Southeast Asia, Thailand hit 45.4 degrees C on April 15 while Vientiane in Lao PDR saw its hottest day ever with 41.4 degrees C on April 15.

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The researchers used three gridded datasets, including the data from India Meteorological Department, to analyse the heatwave event in the context of climate change. The global mean surface temperature from Nasa was used as a measure of the anthropogenetic climate change.

The analysis showed a consistent increase in the heat index (HI) from 1950 to 2023, with roughly 1 degree C increase in average HI between the first and the last decade of the series. “The local values in some places turned out to be much higher, nearing the “extreme danger” range, the study said with the HI reaching 48 degrees C in Dhaka and 50 degree C in Kolkata last month.

Mariam Zacharia, researcher from Grantham Institute, Imperial college London, said the models and observations showed an increasing likelihood of humid heat wave as the experienced in April.

“We found that climate change has made the event at least 30 times more likely in the India-Bangladesh region. It would have been 2 degrees C cooler if there was no climate change. In Thailand, the heat wave would have been a rare, one-in-a-200 years event or heatwave would have been virtually impossible had there been no climate change,” she said.

Global temperature has increased by 1.2 degrees C compared to the pre-Industrial era. The researchers went a step ahead and calculated what happens when the temperature hits the 2 degrees C mark. It would further increase by three times in India-Bangladesh and 10 times in Thailand and Lao PDR, the study said.

The study said adaptation and mitigation strategies, from action plans to early warning systems and disaster response, were the need of the hour.

Anshu Ogra from the School of Public Policy, IIT-Delhi, said vulnerability was an important component for preparing for heatwaves. She said while some cities in India and Bangladesh had action plans, the lack of the same in other areas and countries was a concern.

Emmanuel Raju from the Department of Health, Global Health Section and Copenhagen Centre for Disaster said a number of health implications which come from heatwaves were not spoken about and often not documented.

“Age, gender, occupation, economic status and other issues that allow or disallow access to resources is important while looking at the impacts of heatwave. We should also note that people are recovering from various ongoing disasters, including the pandemic and cyclones. Heatwave adds to it and makes it hard to cope and recover,” he said.