CITY CLIMATE INSIGHTS
23 May 2026 - LocalRisk
England broke its hottest May temperature on record today. LocalRisk data across 1.8 million postcodes shows the heat is not uniform - Cambridgeshire councils recorded 30 or more hot days in 2025 alone, while the picture is very different further north and on the coast.
Spring 2025 was the driest in England for 132 years. As summer 2026 arrives, LocalRisk maps heat, air quality and ground risk by city and postcode - so you
The UK recorded its hottest May temperature on record on 25 May 2026, with 33.5°C measured at Heathrow - breaking a record that had stood for decades. The news coverage will frame this as exceptional. Our postcode data suggests a different way to read it: not as an outlier, but as part of a pattern that is increasingly visible in the numbers.
LocalRisk holds heat risk data for every postcode in Great Britain - built from Met Office UKCP18 climate projections and three years of ERA5 observed weather analysis. Looking across that dataset, the picture is less "everywhere is getting hotter" and more "some places are changing much faster than others."
The strongest signal in our data is the inland east-versus-west and north-versus-south divide. Using ERA5 reanalysis data, we calculated how many days per year each local authority recorded above 25°C across 2023, 2024 and 2025.
The top of the table is dominated by Cambridgeshire and the home counties. South Cambridgeshire, Huntingdonshire and Cambridge itself all averaged 21 hot days per year across those three years - 2023-2025 was an exceptionally warm period for the UK, so these figures reflect recent conditions rather than a long-term baseline. The count climbed sharply in 2025: Huntingdonshire recorded 31 days above 25°C and Cambridge recorded 30.
Compare that to the ERA5 1991-2020 baseline for Cambridge: around 11 hot days per year. The 2025 figure was nearly three times that.
London boroughs sit just below. Camden, Southwark, Tower Hamlets and the rest of the inner London cluster averaged around 19 hot days per year, with 2025 reaching 25. The urban heat island is visible in the data: inner London runs consistently warmer than the surrounding countryside at the same latitude.
Further north, the numbers drop sharply. Newcastle upon Tyne and the wider North East record relatively few days above 25°C across the three-year window. Cumberland, in the far north-west, recorded none at all.
This gradient is not just about latitude. It reflects the influence of the Atlantic to the west (which moderates summer temperatures), continental air masses arriving from the east (which amplify them), and urban heat retention. Geography matters as much as the calendar.
Met Office UKCP18 projections give Cambridge a projected annual average of 37 hot days per year across the 2021-2040 period. The City of London and Tower Hamlets reach 40 to 41. In 2025, Cambridge's observed count reached 30.
These are different numbers - observed weather includes natural year-to-year variability, and projections represent a central estimate across a range of possible outcomes. The projections also use a high-emissions scenario; outcomes under lower emissions pathways would be materially lower, and the full range of modelled outcomes is wide. But the direction of travel is consistent.
At the other end of the scale, Newcastle is projected at around 7 hot days per year as a 2021-2040 average. Manchester and Leeds sit at 18. Bristol at 24. The spread across England is wide, and it means that heat risk is genuinely a local question.
What makes years like 2025 notable is that observed hot-day counts in parts of Cambridgeshire and the home counties are beginning to overlap with the lower end of the projected range for the 2021-2040 period - illustrating how 2025 conditions compared to what the models project for the coming decades.
Hot, still anticyclonic conditions - the kind producing today's record - also tend to accumulate air pollutants. Ground-level ozone builds when sunlight reacts with nitrogen oxides and other vehicle and industrial emissions; fine particles from traffic and industry concentrate when there is little wind to disperse them.
Our air quality data, drawn from Defra UK-AIR monitoring (2024 figures, population-weighted by local authority), shows the baseline position. The City of London records an annual mean PM2.5 of 11.0 µg/m³. Tower Hamlets, Hackney and Westminster are all at or above 9.7 µg/m³. These figures are well within the current UK legal limit of 25 µg/m³, but they represent the starting point - before heat-driven accumulation during extended warm spells.
During anticyclonic conditions, air quality monitoring sites typically record elevated hourly readings in city centres, particularly in the afternoons. People with asthma or other respiratory conditions are generally advised to check daily forecasts from the Met Office or Defra during heat events.
What happens above ground during a dry spell also affects what happens below it. Around 163,000 UK postcodes sit on BGS-classified shrink-swell clay - a soil type that loses volume as it dries and rewets when rainfall returns. Extended dry periods increase soil moisture deficit in these areas.
Shrink-swell clay is concentrated in a band running through central and south-east England - the same areas that tend to experience the highest heat and the lowest rainfall during dry periods. This does not mean homes in these areas are at immediate risk. Most properties on clay soils have coexisted with them for generations. But it is a factor worth knowing about, particularly if you are buying a property built before 1980 on a shallow foundation.
A single record temperature in May does not rewrite the risk profile of a postcode. What builds the picture is a sequence of data: three years of observed hot-day counts, long-term projections, air quality baselines, and ground conditions.
The postcodes that will experience the most significant heat accumulation over the next decade are not evenly distributed. They concentrate in Cambridgeshire and the home counties, in urban areas with low tree cover, and in places with low rainfall and clay-rich soils.
The postcodes where temperatures will remain more moderate - where days above 25°C stay genuinely rare - are mostly coastal, northern, or western. That geography is a real and measurable factor in where it is comfortable to live, even if it rarely appears on a property listing.
You can check heat risk, air quality, flood risk, and subsidence risk for any UK postcode, free, at localrisk.co.uk. Council-level breakdowns - including the observed hot-day counts and UKCP18 projections behind this analysis - are at localrisk.co.uk/local-areas.
ERA5 observed weather: Open-Meteo Historical Weather Archive (ERA5 reanalysis, ECMWF), 2023-2025. Hot-day counts are days above 25°C per local authority, derived from ERA5 grid-cell analysis. ERA5 operates at approximately 28km grid resolution; figures may differ from Met Office station observations, particularly in upland or coastal areas. Heat projections: Met Office UKCP18, RCP8.5 scenario, 50th percentile, 2021-2040 period. Air quality: Defra UK-AIR PM2.5 monitoring network, 2024 data, population-weighted local authority means. Subsidence: British Geological Survey shrink-swell clay risk assessment. Analysis by LocalRisk.