More than 80% of cities across the UK are already vulnerable to urban heat, with almost two thirds projected to face severe heat frailty by the end of the century.
New analysis from Ordnance Survey (OS) found 83% of cities are currently classed as highly vulnerable to urban heat, while all cities are expected to reach this level by 2040. By the end of the century, 45 of 71 cities are projected to enter the severe category.
The urban heat island effect occurs when buildings, roads and other hard surfaces absorb heat during the day and retain it overnight. Limited trees, vegetation and water can further reduce cities’ ability to cool naturally.
Nick Bolton, Chief Executive Officer (CEO) at Ordnance Survey, said: “These findings matter because cities are where millions of people live, work and spend their everyday lives. Extreme and sustained heat can affect people’s health and wellbeing, how comfortable our homes and workplaces are, and put additional pressure on transport, energy and emergency services.”
Portsmouth currently ranks as the most heat-vulnerable city and is expected to remain at the top of the index through to the end of the century. Its dense built environment and limited natural cooling are key factors.
London is also particularly exposed, with the City of London recording the highest built-environment vulnerability and the least effective natural cooling in the analysis.
Leicester is projected to experience one of the largest rises in vulnerability, moving from 10th place today to fourth by the end of the century. Exeter, Nottingham, Bristol and Brighton and Hove are also expected to climb the rankings.
The findings highlight potential implications for energy infrastructure, as rising temperatures can increase cooling demand while putting additional pressure on electricity networks and other essential services.
The analysis compared building density, hard surfaces, tree cover, vegetation and water with observed land temperatures and climate projections.
Milton Keynes provides a contrasting example, ranking 69th for heat vulnerability today due to extensive natural surfaces and comparatively effective cooling. However, it is still expected to move into the high vulnerability category by 2040.
The study suggests expanding green infrastructure and considering heat resilience in future development could help cities manage rising temperatures and protect communities as the climate warms.
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