CITY CLIMATE INSIGHTS
11 July 2026 - LocalRisk
Flood risk and subsidence risk come from different causes - one about water, the other about clay geology - so a council with a high figure on one usually has an unremarkable figure on the other. Cross-referencing LocalRisk's flood and subsidence rankings across all 361 UK councils found the pattern holds almost everywhere: only four councils - Barking and Dagenham, Brent, Harrow and Rochford - appear in the top 20 for both.
Flood and subsidence risk rarely overlap in the UK - only 4 of 361 councils rank in the top 20 for both. See where, and what it means for your postcode.
Flood risk and subsidence risk come from different processes, so there's no reason to expect a council that scores high on one to score high on the other. Flood risk is about water: how close a property sits to a river, the sea, or a floodplain. Subsidence risk in the UK is almost entirely about clay geology: certain soils shrink when they dry out and swell when they get wet again, and that seasonal movement is what can crack walls and distort door frames over time.
We cross-referenced LocalRisk's own flood and subsidence council rankings - both already published separately on the site, but never checked against each other - across all 361 UK council areas. The pattern holds almost everywhere: a council's position on one ranking says very little about its position on the other. Only four councils sit in the top 20 nationally for both: Barking and Dagenham, Brent, Harrow and Rochford.
| Council | Flood risk rank (of 361) | Postcodes at high flood risk | Subsidence risk rank (of 361) | Postcodes on shrink-swell clay | | --- | --- | --- | --- | --- | | Barking and Dagenham | 3rd | 61.4% | 8th | 94.4% | | Rochford | 5th | 52.0% | 15th | 75.8% | | Harrow | 18th | 29.2% | 13th | 85.1% | | Brent | 20th | 26.9% | 1st (tied) | 100.0% |
_Source: LocalRisk analysis of Environment Agency, SEPA and NRW flood data, and British Geological Survey GeoClimate subsidence data, aggregated to council level across all 361 UK council areas. July 2026._
Across the full dataset, the average council sits at 15.0% for flood and 9.3% for subsidence. These four sit above both averages, which is why they stand out as the only overlap - not because either figure alone is unusual. Several other councils score higher than all four of these on a single hazard (Sefton's flood figure and Brent's subsidence figure are both the national maximum) without appearing on the other list at all.
Brent is the clearest illustration of that split: it's tied for the highest subsidence figure in the country, and still only just makes the flood top 20, in 20th place.
Nothing about clay geology makes a place more likely to flood, and nothing about river proximity makes clay more likely to shrink and swell - these four councils aren't dangerous in some combined sense, they're simply where two independently-tracked figures both happen to be elevated. The likely reason is the type of ground involved: low-lying, river- or estuary-adjacent land is, over geological time, also where fine river and estuarine clay tends to settle.
Barking and Dagenham and Rochford both sit on the Thames estuary system - Barking and Dagenham where the River Roding meets the tidal Thames, Rochford on the Roach and Crouch estuaries near Southend - low, flat, historically marshy ground. Harrow and Brent are further inland, on the London Clay Formation that underlies most of inner and outer London; being nowhere near tidal water, their flood exposure comes from smaller rivers and streams draining that same clay-capped ground rather than tidal surge.
It's worth being clear about what a council-level figure can and can't tell you here. The data shows Barking and Dagenham's figures are elevated on both counts; it doesn't show whether the same streets are behind both figures, or whether one part of the borough drives the flood number and a different part drives the subsidence number. Postcode-level data, available for any UK address on the LocalRisk homepage, is the only way to see which applies to a specific property.
The councils at the top of each single ranking make the same point from another angle. Sefton has the UK's highest flood figure, at 71.1%, well above any of the four councils above, but doesn't feature anywhere in the subsidence top 20. Thurrock, second on the flood list, is in the same position.
Subsidence works the same way in reverse. Six of the seven council areas tied at the very top of the subsidence ranking - Westminster, Southwark, Kensington and Chelsea, Lambeth, Hammersmith and Fulham and City of London - sit outside the flood top 20 entirely. Central London's clay geology is close to universal, but the Thames Barrier's protection of the tidal stretch, combined with a dense high-rise property mix that reduces flood exposure per postcode, keeps the flood figure comparatively low there.
None of this means a specific property in Barking and Dagenham, Rochford, Harrow or Brent will face both risks, or that these are unusually risky places to live. A council figure describes the borough, not the individual address, and most of a borough's postcodes sit well below its headline figure. The practical takeaway is a narrow one: in these four areas specifically, it's worth checking both hazards for the exact postcode rather than assuming a good result on one implies a good result on the other, which is a safe enough assumption almost everywhere else in the UK.
Old maps and mature trees near a property are also worth checking regardless of which of the four councils is involved - large trees draw water from clay soils in summer, which can amplify shrinkage. LocalRisk's separate guides cover flood insurance and subsidence insurance in more detail.
Flood figures are drawn from LocalRisk's existing UK flood risk ranking, built from Environment Agency NaFRA2 (England), SEPA Flood Risk Management Maps (Scotland) and Natural Resources Wales flood mapping (Wales), aggregated from postcode level to council level across all 361 UK council areas. A postcode counts as "high flood risk" if at least one property within it has a 3.3% or greater annual probability of river or sea flooding, after existing defences are accounted for.
Subsidence figures are drawn from LocalRisk's existing UK subsidence risk ranking, built from British Geological Survey GeoClimate data, which classifies shrink-swell clay exposure from Improbable through Possible to Probable. Coverage is England and Wales; Scotland's older bedrock has limited clay caps and is not part of the BGS shrink-swell dataset, and Northern Ireland data is not yet integrated into LocalRisk. Both rankings are refreshed quarterly; the figures here reflect the July 2026 refresh.
Every LocalRisk postcode result shows both flood and subsidence bands, alongside heat, air quality, coastal erosion and green space data. Check any UK postcode at localrisk.co.uk.
_Data sources: LocalRisk analysis of Environment Agency, SEPA, Natural Resources Wales and British Geological Survey GeoClimate data, aggregated to council level across all 361 UK council areas. Figures reflect the July 2026 refresh of LocalRisk's flood and subsidence rankings._
At postcode level, the overlap is more common than the council picture suggests. LocalRisk analysis of Environment Agency NaFRA2 flood data and British Geological Survey shrink-swell mapping (July 2026) found 32,264 English postcodes rated High for flood risk that also carry a Probable shrink-swell subsidence rating - roughly 1 in 45 postcodes in England. 73% of them are in London, where clay-basin geology and dense surface-water flood exposure coincide: Barking and Dagenham (1,804 postcodes), Westminster (1,635) and Brent (1,590) top the list. These are postcode-level screening indicators, not property assessments - a High flood band reflects the highest-rated address in the postcode, and Probable shrink-swell describes ground susceptibility rather than damage.