As the El Niño phenomenon arrives, bringing with it rising global temperatures, a new study from the University of Oxford has identified major cities at the highest risk from extreme heat. The research, published in Sustainable Cities and Societies, analyzed the hazard exposure, vulnerability, and coping capacity of 220 cities with populations exceeding one million.
The findings indicate that over 95 percent of the cities most at risk are concentrated in South and Southeast Asia, and Sub-Saharan Africa. Lead author Nethmi Jayaratne Kariyawasam emphasized that heat risk is not solely determined by exposure to high temperatures but also by multifaceted factors including vulnerability and the ability to cope.
"In many major cities, particularly across Asia and Africa, extreme heat coincides with high vulnerability and limited coping capacity," Kariyawasam stated. "This combination can substantially increase heat risk and, in some cases, have life-threatening consequences."
The study utilized a set of risk indicators, including demographic and socioeconomic conditions that can heighten susceptibility to heat-related illness and mortality, such as age and financial resources. Access to cooling infrastructure, like air conditioning, and ecological buffers, such as tree cover, were also factored into the assessment.
Al Basrah, Iraq, was identified as the city most vulnerable to extreme heat, followed by Ahmadabad, India, Bamako, Mali, and Nagpur, India. Several popular tourist destinations were also flagged as high-risk areas. Ho Chi Minh City, Vietnam, ranked 16th, while Cairo, Egypt, was 22nd, and Bangkok, Thailand, was 38th.
Conversely, London was found to be the least vulnerable among the analyzed cities, with Glasgow and Birmingham ranking 215th and 213th, respectively.
"This study provides the first globally harmonised and directly comparable assessment of urban heat risk across cities worldwide," said co-author Jesus Lizana. "This provides a powerful tool for identifying where adaptation efforts are most urgently needed."
Researchers hope the findings will underscore the urgent need for global mitigation measures. Co-author Radhika Khosla noted the importance of a nuanced approach to adaptation, stating, "Our study shows that heat risk planning needs to explicitly address not just exposure to high temperatures, but vulnerability and coping capacity."
Khosla also raised concerns about an over-reliance on energy-intensive cooling methods like air conditioning, particularly as many cannot afford it. She suggested prioritizing passive cooling and low-energy technologies as initial steps towards ensuring thermal comfort and safety for all urban populations.
Heatwaves are becoming more frequent, longer, and more intense, leading to increased mortality, infrastructure failures, and economic losses globally. With more than half the world's population residing in cities and this figure projected to rise to two-thirds by 2050, urban areas are increasingly becoming critical hotspots for climate impacts.