A recent study has found that humid heatwaves, that occurred less than once in a century in India and Bangladesh, can now be expected to happen once in five years. If temperature rise reaches 2°C—as is expected to happen within around 30 years if emissions are not cut rapidly—events like this will occur, on average, at least once every two years.
This conclusion comes from a rapid attribution analysis by an international team of leading climate scientists part of the World Weather Attribution group. Human-caused climate change made April’s record-breaking humid heatwave in Bangladesh, India, Laos and Thailand at least 30 times more likely the study concludes.
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 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.
Heat index is a measure that combines temperature and humidity and reflects more accurately the impacts of heatwaves on the human body.
Heatwaves are amongst the deadliest natural hazards with thousands of people dying from heat-related causes each year and many more suffering other severe health and livelihood consequences. However, the full impact of a heatwave is often not known until weeks or months later, once death certificates are collected, or scientists can analyse excess deaths. Many places lack good record keeping therefore currently available global mortality figures due to heatwaves are likely to be an underestimate.
While people in the affected regions are used to hot and humid temperatures, those who are more physiologically susceptible to heat (e.g. due to pre-existing conditions, age, disability etc.) and/or are more exposed due to their occupation (e.g. outdoor workers, farmers) are at highest risk of heat-related health impacts. Such exposure and vulnerability are intensified by societal disadvantage based on factors such as socio-economic status, religion, caste, gender, migration, and living conditions. In addition, factors such as air pollution, the urban heat island effect, and wildfires further compound health impacts, particularly among the most vulnerable populations.
Among the study’s other major finding is that while there are a range of solutions to heat-related harms from the individual to the regional level, these are implemented as patchwork, in various degrees, across the countries studied, with India having the most advanced heatwave planning.
Solutions, such as self-protective action, early warning systems for heat, passive and active cooling, urban planning, and heat action plans can be effective at reducing fatalities and other negative impacts. In fact, heat-related fatalities have decreased in regions where heat action plans have been in place, e.g. Ahmedabad and in Odisha. 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.