Almost all cities facing the greatest danger from extreme heat are in Asia and Africa, where searing temperatures collide with poverty and little means to cope, according to a new Oxford study.
The study assesses 205 cities with populations of over one million on three fronts: how hot they get, how vulnerable their people are, and how well they can cope.
It shows that Al Basrah in Iraq is the city most at risk. The assessment further reveals that some 95 per cent of the cities at the highest risk are in South Asia, Southeast Asia and Sub-Saharan Africa.
India, Pakistan, Nigeria, and Ghana host the largest number of cities with high risk scores, according to the study published in the journal Sustainable Cities and Society.
Major tourist destinations and business hubs feature in the top 50, such as Cairo in Egypt, Bangkok in Thailand, Hanoi in Vietnam, and Jaipur in India.
The ranking is the first globally consistent comparison of urban heat risk, researchers say, and moves beyond earlier assessments that measured only how hot cities get.
"It isn't just exposure to hot temperatures that matters for risk. Our study highlights the importance of multi-faceted global heat risk assessments, which reveal the diverse pathways through which urban heat risk emerges," Nethmi Jayaratne Kariyawasam, lead author and DPhil researcher at the Oxford Smith School of Enterprise and the Environment, said.
"In many major cities, particularly across Asia and Africa, extreme heat coincides with high vulnerability and limited coping capacity," Ms Kariyawasam added. “This combination can substantially increase heat risk and, in some cases, have life-threatening consequences.”
The research measures heat exposure using cooling degree days, a metric that captures cumulative heat stress by combining air temperature, humidity, wind and radiant heat. Vulnerability is assessed through factors like the share of young children and people over 65, income levels, and access to air conditioning, while coping capacity covers tree cover, vegetation, and electricity prices.
The results show that heat alone doesn’t determine risk. Some of the world's hottest cities, including Bangkok, Kuala Lumpur in Malaysia and Jeddah in Saudi Arabia, rank outside the top decile of overall risk because greater urban greening and more affordable energy help them cope.
Others face severe danger despite more moderate temperatures. Karachi and Faisalabad in Pakistan and Kaduna in Nigeria rank among the highest-risk cities because of low incomes, sparse vegetation, and limited access to cooling, the study found.
The findings come as Europe and the UK are scorched by a heatwave. France recorded nearly 2,000 excess deaths during the last week of a record-breaking heatwave in June as forecasters warned of further extreme temperatures on the continent in the next few days.
"Our study shows that heat risk planning needs to explicitly address not just exposure to high temperatures, but vulnerability and coping capacity,” Dr Radhika Khosla at the Smith School of Enterprise and the Environment who co-supervised the research said.
"Air conditioning demand is increasing worldwide but many cannot afford it. And if we over-rely on this energy-intensive form of cooling, we risk further global warming in a vicious cycle. In order to scale adaptation and thermal comfort for all, we must consider a nuanced approach to keeping people safe, sequencing solutions with passive cooling and low-energy technologies such as fans and coolers being the first step."
Dr Jesus Lizana, associate professor in engineering science and co-supervisor of the study, said that it provided “the first globally harmonised and directly comparable assessment of urban heat risk across cities worldwide", offering a tool for identifying where adaptation was most urgently needed.
The researchers say that the ranking is a comparative tool rather than a prediction and that city-wide scores can mask stark inequalities within the cities, where residents of informal settlements and low-income households face far higher risks than averages suggest.
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