Portsmouth, Leicester, Exeter most
Ordnance Survey analysis identifies Portsmouth as Britain's most heat-vulnerable city now and in 2100, with Leicester, Exeter, Bristol and Nottingham also
Portsmouth is the British city most vulnerable to extreme heat today and will remain so until the end of the century. Leicester is projected to show the biggest rise in the national heat vulnerability rankings, climbing from 10th to fourth by 2100, according to new research from Ordnance Survey, the Met Office and data firm 4 Earth Intelligence.
The analysis created a heat vulnerability index for all 71 chartered cities in Great Britain. It found that concrete, asphalt and buildings in urban areas absorb solar radiation and act like giant radiators, holding heat at night. Cities can be up to 10C hotter than surrounding rural areas.
Areas with the least tree cover, green space and waterways face the greatest risk. This summer was provisionally the UK's hottest on record.
Cities Reaching Severe Heat Levels
By 2040, all 71 cities will reach a high level of heat vulnerability on the index's 1-to-5 scale. By the turn of the century, almost two-thirds could reach the most severe level. The cities facing the most severe impact by 2100 are predicted to be Portsmouth, the City of Westminster, Plymouth, Leicester and Exeter.
Exeter and Nottingham will also rise into the ten most vulnerable cities by 2100, alongside Bristol and Brighton and Hove.
Nick Bolton, chief executive of Ordnance Survey, said the findings were critical for planning. "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," he said.
The Urban Heat Island Effect
The City of London records the highest built-environment score and the least effective natural cooling of any city, due to its concentration of buildings and hard surfaces. Westminster ranks third for overall heat vulnerability today and second in both future periods behind Portsmouth.
A study for the mayor of London put the total economic cost of the 2022 London heatwaves at £1.5bn. This included productivity losses, health impacts and disruption to education and transport.
Portsmouth leaders have identified areas including Somerstown, Portsea, Southsea and Fratton as particularly exposed. They note that limited green areas and hard surfaces overlap with areas of deprivation.
Building Resilience and Cooler Cities
The index combined current temperatures, structural characteristics of the built environment and future climate projections. Jonathan Hendry, chief executive of 4 Earth Intelligence, said exposure varies street by street. "The areas consistently subjected to higher temperatures than their surroundings are the ones that overheat first during a heatwave," he said.
His firm is mapping thermal threats to create blueprints for urban resilience. This supports decisions on where to site heat refuges and how to plan emergency responses in advance.
Cities Best Coping with Heat
Among cities coping best is Milton Keynes. It ranks 69th out of 71 for heat vulnerability today. Milton Keynes has the lowest built-environment vulnerability in England and the most effective natural cooling of any city in the analysis.
The city has 46 square kilometres of natural surfaces against almost 40 square kilometres of hard, made surfaces. This balance provides a model for urban cooling as temperatures rise across Britain.
