New research from Ordnance Survey (OS) highlights a growing risk of urban overheating across UK cities over the coming decades. This analysis, conducted in the wake of a summer marked by record-breaking temperatures, projects a marked increase in heat vulnerability from 2040 through to 2100.
The study introduced a Heat Vulnerability Index that incorporates numerous factors, including building density and height, the extent of hard surfaces, tree canopy coverage, open vegetation, and water bodies within cities across England, Scotland, and Wales. This index also integrates observed land surface temperature data alongside projections of air temperature from Met Office climate models.
Findings indicate that currently, about 83 percent of UK cities are classified as “highly vulnerable” to urban heat, with the remaining 17 percent considered “moderately vulnerable.” However, the forecast is more dire: by 2040, all cities are expected to fall into the high vulnerability category, and by the end of the century, nearly two-thirds (63 percent) are projected to reach “severe” heat vulnerability, the highest level on the index.
One of the primary contributors to this trend is the urban heat island effect, where cities retain significantly more heat than rural areas. This occurs because built-up environments, with dense structures and extensive hard surfaces like concrete and asphalt, absorb heat during the day and release it slowly at night, causing urban temperatures to be as much as 10°C higher than surrounding countryside. Tall buildings and narrow streets further exacerbate the problem by restricting air flow that would otherwise cool the environment.
Experts emphasize that the materials and design of urban infrastructure play a critical role in heat retention. The prevalence of “grey infrastructure,” composed of heat-absorbing and heat-reflective materials, creates an environment that traps and re-emits heat. Additionally, limited incorporation of natural “green and blue” infrastructure—such as parks, trees, rivers, and lakes—reduces natural cooling mechanisms like shading and evaporation.
Vegetation can significantly lower temperatures; shaded areas under tree canopies can be 10 to 12°C cooler than surrounding spaces, while replacing asphalt with grass or shrubs can reduce surface temperatures by up to 8°C. Water bodies also contribute cooling through evaporation, but many urban waterways have been diverted or covered over to make way for development.
Another factor worsening urban heat is human activity, including transportation and the use of air conditioning (AC). While AC provides relief indoors, it discharges heat and greenhouse gases outdoors, intensifying the overall heat island effect. This creates a feedback loop where heat absorption and retention cycle continuously, driving temperatures ever higher.
The risk associated with overheating is influenced not just by temperature increases but also by the combination of urban density, extent of hard surfaces, availability of green space, and the design and performance of housing. As noted by researchers, many UK cities have historically not been designed with overheating in mind, leaving them vulnerable to rising temperatures under climate change.
Addressing this challenge, experts point to the need for strategic urban planning that integrates more green and blue infrastructure, reduces heat-absorbing surfaces, and improves building design. Without such measures, the warming trend in UK cities threatens to impact livability, health, and energy consumption in the decades to come.