Extreme Heat Intensifying in Global Cities: Study Reveals 26% Rise in Very Hot Days
A new analysis reveals a significant increase in extreme heat events across major cities worldwide, with a 26% rise in the number of very hot days recorded between 1994 and 2024. The study, examining 43 cities with a combined population of approximately 470 million, highlights a particularly alarming trend: the three years with the highest number of extremely hot days have all occurred within the last six years, culminating in a record-breaking 2024.
The analysis showed 1,612 very hot days were recorded across the selected cities in 2024 – 196 more than in 2019 (the second highest year) and 52% higher than the number recorded in 1994. Cities experiencing record heat included Antananarivo (Madagascar), Cairo (Egypt), Johannesburg (South Africa), Kinshasa (Democratic Republic of Congo), Manila (Philippines), Rome (italy), Tokyo (japan), Washington DC (US), and Yaounde (Cameroon).
The impact of rising temperatures is not uniform. the study emphasizes the heightened vulnerability of residents in informal settlements, particularly in cities like Delhi, where the population has grown substantially as 2013. These communities often lack adequate housing and infrastructure, exacerbating the effects of sustained high temperatures.
The trend extends beyond Asia. In brazil, Brasilia experienced a dramatic increase from an average of three days above 35 degrees Celsius between 1994 and 2003, to 40 such days in the most recent decade. Even Sao Paulo, traditionally known for its milder climate, recorded 120 days exceeding 30 degrees Celsius in 2024 – the highest in the study period.
Europe is also experiencing a marked increase in extreme heat. Rome,Italy,saw the average number of days above 35 degrees Celsius rise from 11 (1994-2003) to 24 in the last decade. Madrid (Spain) experienced a similar shift, with an increase from 25 days to 47 between the earlier period and 2015-2024. Berlin (germany) also recorded a rise in very hot days.
“Global temperatures are rising faster than governments probably expected and definitely faster than they seem to be reacting,” stated Anna walnycki,a researcher at IIED. She further warned, “Failing to adapt will condemn millions of city dwellers to increasingly uncomfortable and even perilous conditions as of the urban heat island effect.”
Walnycki emphasized that the poorest populations, nonetheless of location – whether in London, luanda, or Lima – will bear the brunt of the impact, with those in low-income or unplanned communities in the global South facing the most severe consequences due to inadequate housing and infrastructure.
The IIED report urges cities to prioritize funding for improvements such as building insulation and ventilation, the development of heat action plans, and the creation of shade cover. It also stresses the importance of ensuring new construction is designed to withstand a warming climate. The analysis notes that nearly one-third of the global urban population resides in informal settlements, making them particularly susceptible to deadly heatwaves. The population of the 43 cities studied is projected to increase substantially in the coming decades.