Human-caused climate change made April's record-breaking humid heatwave in Bangladesh, India, Laos and Thailand at least 30 times more likely, according to rapid attribution analysis by an international team of leading climate scientists as part of the World Weather Attribution group. The study also concludes that the high vulnerability in the region, which is one of the world's heatwave hotpots, amplified the impacts.
In April, parts of south and southeast Asia experienced an intense heatwave, with record-breaking temperatures that passed 42ºC in Laos and 45°C in Thailand. The heat caused widespread hospitalisations, damaged roads, sparked fires and led to school closures. The number of deaths remains unknown.
Across the world, climate change has made heatwaves more common, longer and hotter. To quantify the effect of climate change on the Asian heatwave, scientists analysed weather data and computer model simulations to compare the climate as it is today, after about 1.2°C of global warming since the late 1800s, with the climate of the past, following peer-reviewed methods.
The analysis looked at the average maximum temperature and maximum values of a heat index for four consecutive days in April across two regions, one covering south and east India and Bangladesh, and a second one including all of Thailand and Laos. The heat index is a measure that combines temperature and humidity and reflects more accurately the impacts of heatwaves on the human body.
In both regions, the researchers found that climate change made the humid heatwave at least 30 times more likely, with temperatures at least 2°C hotter than they would have been without climate change. Until overall greenhouse gas emissions are halted, global temperatures will continue to increase and events like this will become more frequent and severe.
In Bangladesh and India, events like the recent humid heatwave used to occur less than once a century on average; they can now be expected around once in five years, and if temperature rise reaches 2°C - as will happen within around 30 years if emissions are not cut rapidly - events like this will occur, on average, at least once every two years.
In Laos and Thailand, the scientists found that an event like the recent record humid heatwave would have been nearly impossible without the influence of climate change, and it is still a very unusual event that can only be expected around once in 200 years, even with the influence of human-caused climate change. But if temperature rise reaches 2°C, it will become much more common, occurring about once in 20 years.
While high temperatures are the norm in south and southeast Asia, early heatwaves such as this one are particularly damaging. People who are most exposed to the sun and vulnerable populations are routinely the worst impacted. The current patchwork of heatwave solutions must be improved to account for inequalities and existing vulnerabilities, the scientists said, adding that heat action plans should be inclusive and comprehensive, and ensure access to basic services, such as water, electricity and health care.
The study was conducted by 22 researchers as part of the World Weather Attribution initiative, including scientists from universities and meteorological agencies in India, Thailand, Australia, Denmark, France, Germany, Kenya, the Netherlands, the UK, and the United States.
Quotes
Chandra Sekhar Bahinipati, Indian Institute of Technology Tirupati, India, said:
"Although we have recognized heatwaves as one of the deadliest disasters, particularly in countries like India, Bangladesh, and Thailand, there is a lack of knowledge with respect to who is vulnerable, loss and damage estimation, household coping mechanisms, and the most effective heat action plans. Except for the human casualties, other economic and non-economic loss and damage indicators are not documented. This creates a dearth in assessing the extent of risk, who is vulnerable, and also operationalizing any adaptation planning."
Friederike Otto, Senior Lecturer in Climate Science at the Grantham Institute for Climate Change and the Environment, said:
"We see again and again that climate change dramatically increases the frequency and intensity of heatwaves, one of the deadliest weather events there are. Still, heat action plans are only being introduced very slowly across the globe. They need to be an absolute priority adaptation action everywhere, but in particular in places where high humidity enhances the impacts of heatwaves."
Emmanuel Raju, Director of Copenhagen Centre for Disaster Research at the University of Copenhagen, said:
"This is another disaster that highlights the need to reduce vulnerability and think deeper about the limits to adaptation. As it often happens, marginalised people are the worst affected. Many of them are still recovering from the pandemic, and from past heatwaves and cyclones, which leaves them trapped in a vicious cycle. It is fundamental to implement mitigation and adaptation strategies to avoid visible and invisible loss and damage".
About this study
World Weather Attribution (WWA) is an international collaboration that analyses and communicates the possible influence of climate change on extreme weather events, such as storms, extreme rainfall, heatwaves, cold spells, and droughts. It is led by Dr Fredi Otto, Senior Lecturer in Climate Change at the Grantham Institute - Climate Change and the Environment at Imperial College London and Sjoukje Philip and Sarah Kew at KNMI.
Since WWA started in 2014, the group has developed methods to do extreme event attribution quickly but thoroughly. Read a detailed description of the methods and links to the peer-reviewed studies developing these methods.
Previous studies by WWA include research that found that climate change exacerbated floods in Nigeria and other parts of West Africa this year. WWA studies have also shown that this year's drought in the Northern Hemisphere was made more likely by climate change and that it increased the rainfall that led to Pakistan's deadly flooding, but that it was not the main driver in Madagascar's 2021 food crisis.
Study authors:
- Mariam Zachariah, Grantham Institute, Imperial College London, UK
- Robert Vautard, Institut Pierre-Simon Laplace, CNRS, Sorbonne Université, Paris, France
- Chaithra S T, Centre for Atmospheric Sciences, Indian Institute of Technology Delhi, India
- Joyce J Kimutai, Grantham Institute, Imperial College London, UK
- Arulalan T, India Meteorological Department, Ministry of Earth Sciences, Gov. of India, Centre for Atmospheric Sciences, Indian Institute of Technology Delhi, India
- Krishna AchutaRao, Centre for Atmospheric Sciences, Indian Institute of Technology Delhi, India
- Clair Barnes, Grantham Institute, Imperial College London, UK
- Roop Singh, Red Cross Red Crescent Climate Centre, The Hague, the Netherlands
- Maja Vahlberg, Red Cross Red Crescent Climate Centre, The Hague, the Netherlands
- Julie Arrgihi, Red Cross Red Crescent Climate Centre, The Hague, the Netherlands; Global Disaster Preparedness Center, Washington DC, USA; University of Twente, The Netherlands
- Emmanuel Raju, Department of Public Health, Global Health Section & Copenhagen Centre for Disaster
- Upasna Sharma, School of Public Policy, Indian Institute of Technology Delhi, India
- Anshu Ogra, School of Public Policy, Indian Institute of Technology Delhi, India
- Chaya Vaddhanaphuti, Department of Geography, Chiang Mai University, Thailand
- Chandra Sekhar Bahinipati, Department of Humanities and Social Sciences, Indian Institute of Technology Tirupati, India
- Petra Tschakert, School of Media, Creative Arts and Social Inquiry, Curtin University, Perth, Australia
- Ram Chandrasekaran, School of Media, Creative Arts and Social Inquiry, Curtin University, Perth, Australia
- Carolina Pereira Marghidan, Red Cross Red Crescent Climate Centre, The Hague, the Netherlands; Faculty of Geo-Information Science and Earth Observation (ITC), University of Twente, Enschede, the Netherlands
- Arpita Mondal, Civil Engineering Department, Indian Institute of Technology Bombay, India; IDP in Climate Studies, Indian Institute of Technology Bombay, India
- Clemens Schwingshackl, Department of Geography, Ludwig-Maximilians-Universität München, Munich, Germany
- Sjoukje Philip, Royal Netherlands Meteorological Institute (KNMI), De Bilt, The Netherlands
- Friederike E L Otto, Grantham Institute, Imperial College London, UK
