Climate Change Made the April 2023 Heat Wave Across India 30 Times More Likely

And as the world continues to warm up, climate change will increase the chances of such an event occurring, the report said.

Kochi: Human-induced climate change made the April 2023 heat wave across India and Bangladesh 30 times more likely, as per a report by an international team of climate scientists as part of the World Weather Attribution group published on May 17.

Their report, which also studied the heat wave that swept across parts of Thailand and Laos, found that the heat wave would have been “virtually impossible” in these countries if it wasn’t for climate change.

And as the world continues to warm up, the likelihood of an event like the April 2023 humid heat wave recurring would increase, the report said. In India and Bangladesh, it would increase by three times if we reach the 2°C warming threshold, suggesting that such an event could occur every one or two years.

While India is better off when it comes to having systems in place (such as Heat Action Plans) to prepare for and deal with heat waves, there are still more improvements to be made such as ensuring differentiated vulnerability assessments that take into account factors such as gender, economic status and occupation, the authors said. Policies should also consider social protection systems such as compensatory mechanisms in place for vulnerable communities, they added.

The April 2023 heat wave 

Large parts of South Asia witnessed high temperatures between the second and fourth week of April this year. Temperatures soared in Thailand and Laos during this time. The city of Tak in Thailand recorded the country’s hottest ever temperature (45.4°C), as did two cities in Laos. Bangladesh recorded its highest maximum temperature in several decades (mercury touched 40.6°C) and registered several cases of heat strokes among people. 

In India too, April was extremely hot. Pragyaraj in Uttar Pradesh recorded 44.6°C on April 17. The India Meteorological Department’s (IMD) predictions of heat wave conditions over north, central and east India – including the states of Maharashtra, Bihar, Odisha, Andhra Pradesh, Delhi-NCR – came true over these days. On April 16, 13 people lost their lives in Navi Mumbai, Maharashtra, due to exposure to the heat at a public event; there were reports of more than 600 hospitalisations too.

To study this heat wave and if it was linked to climate change in any way, 23 climate scientists as part of the World Weather Attribution group (a collaborative initiative between several international institutes including the Indian Institute of Technology that conduct rapid attribution analyses to assess the role of climate change in the occurrence of an extreme weather event) got together. The team used observed temperature data and climate model simulations to study the prolonged heat wave conditions that occurred over parts of South Asia. They estimated a Heat Index (HI, which accounts for the impacts of both high temperatures and humidity levels on the human body) averaged over four days, across two specific regions: south and central India (the states of West Bengal, Andhra Pradesh, Tamil Nadu, Kerala, Goa and Maharashtra) and Bangladesh, and Thailand and Laos.

Representative image of a heat wave. Photo: PTI/Kamal Kishore

Role of climate change 

The team found that estimated HI values exceeded 41°C – the threshold considered as “dangerous” for the human body to cope with the temperature increase – over large parts of both South Asian regions between the second and fourth weeks of April. In a few areas, it even neared 54°C or above, which is considered “extremely dangerous” for human life.

They found that climate change made the April 2023 heat waves across India and Bangladesh 30 times more likely. Due to climate change, such an event – which has a chance to occur once in five years – is now 2°C hotter in terms of the Heat Index than before. 

Without climate change, the heat waves across Thailand and Laos would have been “virtually impossible”, said Mariam Zacharias, one of the co-authors of the report, in an online press briefing on May 17. This event occurring in Thailand and Laos would have been very rare had there been no climate change. 

Their climate models suggest that in future, there will be a “strong increase in likelihood and intensity” of humid heat events such as the one April 2023 witnessed in both regions. As global warming increases, the likelihood of an event like the April 2023 humid heat wave recurring in India and Bangladesh would increase by three times (occurring once every one or two years), if we reach the 2°C warming levels above pre-industrial times, the report found. In Thailand and Laos, it would be 10 times more likely in such a scenario.

Though India and Bangladesh have developed Heat Action Plans, Thailand and Laos don’t have any yet, the report noted. Heat-related fatalities have decreased in regions where HAPs have been implemented, such as in Ahmedabad and Odisha in India, it said. 

“However, these solutions are often out of reach for the most vulnerable people, highlighting the need to improve vulnerability assessments and design interventions that account for group-specific needs,” the report read.

Also Read: How Well Do You Know Your Heatwave? A Study of India Data

Need differentiated vulnerability assessments

There are a number of health implications that heat waves cause that are not talked about or recorded, including fatalities, said Emmanuel Raju, of the Department of Public Health, Global Health Section and Copenhagen Centre for Disaster, Denmark, in a press briefing to the media. Factors such as age, gender, economic status, caste, hierarchy and informality allow or disallow access to resources to tackle heat wave impacts, he said. He took the example of informality: this region has a very high population in these regions that live in informal settlements, which bring in questions of access to resources such as access to health care or cooling and fans.

Street vendors, farmers, and others in the informal economy are more vulnerable and heat waves impact their abilities to work, including by causing not just health concerns but also reduced incomes, he said.

“It’s important to talk about who can adapt, who can cope, and who has resources to be able to do this,” Raju said. We need to talk about both adaptation and mitigation in the context of climate change and discussions on loss and damage, he added. 

Vulnerabilities are an important component in preparing for heat waves and are differentiated across and within the countries, said co-author of the report Anshu Ogra, School of Public Policy, Indian Institute of Technology Delhi, India, in the press briefing. Vulnerability assessment in HAPs, therefore, becomes crucial, she said. 

“There is an important need to institutionalise these processes across the board, and talk about it in terms of policy,” added Raju. For example, there is no access to relief, such as compensation or any specific social protection system, afforded to communities that are impacted most by heat waves, he said.