From Delhi to Rome: Cities record alarming surge in extreme hot days

A study by the UK-based International Institute for Environment and Development (IIED) has revealed that extreme heat days in major cities worldwide have increased by more than a quarter over the past three decades.

Researchers analysed temperature data from 43 key cities, including the 40 most populous capitals, and found that days above 35°C rose from an annual average of 1,062 between 1994 and 2003 to 1,335 between 2015 and 2024—a 26 per cent jump.

The year 2024 was the hottest in the study period, recording 1,612 very hot days across the selected cities, 196 more than 2019, the second-highest year. The top three years for extreme heat have all occurred in the past six years: 2024, 2023, and 2019.

Cities where extreme heat records were broken in 2024 include Antananarivo (Madagascar), Cairo (Egypt), Johannesburg (South Africa), Kinshasa (Democratic Republic of Congo), Manila (Philippines), Rome (Italy), Tokyo (Japan), Washington DC (US), and Yaounde (Cameroon).

Delhi, where population pressures have sharply increased since 2013, is among the cities struggling most with worsening heat stress. The analysis warns that residents in informal settlements are particularly at risk due to poor housing and limited infrastructure.

The study also found rising temperatures in Europe. Rome now averages 24 days above 35°C compared to 11 in the late 1990s, while Madrid’s count increased from 25 to 47 over the same period. Berlin also recorded more hot days.

IIED researcher Anna Walnycki said governments are not keeping pace with the accelerating rise in global temperatures. “Failing to adapt will condemn millions of city dwellers to increasingly uncomfortable and even dangerous conditions because of the urban heat island effect,” she warned.

The report stressed that poorer communities—whether in London, Luanda, or Lima—will bear the brunt of worsening conditions, with the greatest impacts in low-income or unplanned settlements in the Global South.

IIED has called for urgent investment in urban resilience, including improved building insulation, ventilation, shade cover, and heat action plans to safeguard vulnerable populations.
(With PTI inputs)