2026 shown against confirmed surge years 2018 and 2022, plus 2024 (no surge) and 2025 (confirmed surge). Dashed lines mark the 218mm and 320mm risk markers.
Square 161 (SE England / Greater London area). Deciduous tree SMD* is the primary tracking metric for shrinkable clay subsidence risk.
* Soil moisture deficit (SMD) is a measure of how dry the soil is relative to its maximum water-holding capacity. A high SMD means the ground has lost significant moisture. In areas underlain by shrinkable clay, high SMD causes the clay to contract and crack — the principal mechanism behind subsidence damage to buildings and infrastructure.
† The 218mm and 320mm risk markers are Geobear-defined thresholds derived from analysis of historic subsidence case report data and previous surge years. They are not official Met Office or industry-standard figures. The 218mm level represents the SMD at which Geobear's historic data shows a material increase in subsidence activity on shrinkable clay soils; the 320mm level is associated with extreme and sustained surge conditions.
Most recent four weeks of Square 161 data. Week-on-week SMD change shows the direction of travel.
| Week ending | Sun (hrs) | Rain (mm) | SMD grass | SMD deciduous | Wk change |
|---|
Soil moisture is lost through evapotranspiration — the combined process of water evaporating from the soil surface and transpiring through plant leaves. In summer, this is the primary mechanism driving soil drying. Large deciduous trees such as oak, willow, poplar and elm extract water from deep within shrinkable clay layers via extensive root systems, even when the surface appears dry. Their evapotranspiration rates are substantially higher than grass, which is why deciduous SMD diverges from grass SMD as the season progresses — and why heatwaves, which dramatically accelerate transpiration rates, cause such rapid SMD jumps.
This is why this dashboard tracks deciduous tree SMD rather than grass SMD. It better reflects the deep moisture extraction in clay soils that causes shrinkage and ground movement beneath buildings. MORECS deciduous SMD is modelled using canopy resistance and available water capacity parameters calibrated specifically for tree-covered soils, based on the Hough & Jones (1997) methodology.
Sources: MORECS Square 161 week ending 3 Nov 2026; NOAA CPC Oct 2026; elninolive.com weekly tracker; Met Office autumn/winter 2026–27 outlook.
However, the week to 3 November brought only 3.6mm of rain, and SMD edged back to 283.5mm — a reminder that one event does not reverse a deficit of this scale. Cumulative rainfall since 28 July: approximately 115mm across 14 weeks. Recovery is confirmed and meaningful, but sustained 20mm+ per week over multiple consecutive weeks is still required to continue the trajectory. In 2022, recovery from ~300mm in October took a further 8 weeks of consistent rainfall.
El Niño has accelerated dramatically: NOAA’s weekly Niño 3.4 reading reached +3.4°C on 28 October 2026 — approaching the record 1997/98 event peak of +3.6°C. CPC maintains an El Niño Advisory. The Met Office autumn/winter 2026–27 outlook says a wetter, milder and stormier UK is now 1.5–2 times more likely than normal — consistent with past strong El Niño patterns. If realised, this would support continued recharge through November and December.
Note on 29 August 2026 data: the MORECS reading for the week ending 29 August 2026 is unavailable. The chart and table skip directly from 25 August to 1 September. All other weeks from 1 September onward are confirmed from official MORECS Square 161 data.
The following is an interpretive assessment based on historical MORECS patterns and current climate signals. It is speculative and should not be treated as a forecast.
SMD will remain at or near the model ceiling until sustained and repeated rainfall events drive meaningful recharge into the deep clay root zone. This is not triggered by a single shower — it requires the kind of persistent Atlantic low-pressure systems that typically establish themselves from late September onwards as the jet stream shifts southward for autumn. Based on the two most recent confirmed surge years, that process looks like this:
| Year | 320mm crossed | Recharge began | Weeks above 320mm | Peak claims activity |
|---|---|---|---|---|
| 2018 | Wk 29 (mid-Jul) | Late Oct (wk 43) | ~14 weeks | Aug–Oct 2018 |
| 2022 | Wk 26 (late Jun) | Early Oct (wk 40) | ~14 weeks | Jul–Oct 2022 |
| 2025 | Wk 30 (late Jul) | Mid-Oct (wk 42) | ~12 weeks | Aug–Oct 2025 |
| 2026 (projected) | Wk 28 (mid-Jul) | Late Sep–Oct (wk 39–43)? | ~11–15 weeks (speculative) | Aug–Oct–Nov 2026? |
Applying the same pattern to 2026: SMD crossed 320mm in week 28. If recharge follows the same late-September to mid-October timeline as 2022 and 2025, the surge would remain active for approximately 11–15 weeks — meaning SMD would remain above 320mm until around late September or mid-October 2026.
There is one factor that could extend this: a very strong El Niño. During strong El Niño winters, the UK tends to see wetter and stormier conditions — but this typically becomes the dominant pattern from November onwards, not September or October. The autumn transition period (September–October) tends to be less reliably wet in El Niño years than mid-winter. This means the surge may not benefit from early El Niño-driven autumn rainfall; the recharge signal is more likely to come from the return of normal Atlantic westerly flow in late September.
Scientific basis: Comas et al. (2002) Plant and Soil; McCormack et al. (2015) New Phytologist; Mokany et al. (2006) Global Ecology and Biogeography. Hypothesis on compounding risk is labelled as such and has not been formally tested for UK shrinkable clay soils.
In a normal year, October and November rainfall progressively recharges the root zone. Clay soils regain moisture, swell back towards their winter equilibrium, and the risk of foundation movement subsides. By the time deciduous trees begin drawing water again in April, the soil profile is fully or near-fully recharged — effectively resetting the starting conditions for the following season.
That reset is beginning, slowly, in autumn 2026. The first meaningful rainfall of the season — 15.2mm in the week to 20 October — brought SMD to 327.4mm, the first reading below the model ceiling since early September. With approximately 50mm of cumulative rainfall since 28 July across 12 weeks, clay soils across south-east England remain deeply depleted under deciduous tree root zones. If October and November fail to deliver sustained rainfall — defined as 20mm or more per week across multiple consecutive weeks — soils will enter winter and spring 2027 in an abnormally depleted state. Claims from the 2026 season, which typically peak 6–18 months after peak drying, may therefore extend further into 2027 than the seasonal pattern alone would predict.
There is a second factor, distinct from soil moisture alone. Research on drought-stressed trees documents a consistent response: when water becomes scarce at normal rooting depths, trees extend their root architecture downward and laterally — investing more carbon in root growth to access deeper moisture reserves (Comas et al. 2002; McCormack et al. 2015; Mokany et al. 2006). A tree that drought-stressed through 2025 and again through 2026 has already built the root architecture to draw water from deeper down — which means the ground beneath it dries out faster, even if the tree itself copes better next season.
Hypothesis (not yet formally tested for UK shrinkable clay soils): Two consecutive drought years — 2025 and 2026 — may have produced a compounding effect that the MORECS model does not capture. MORECS uses a fixed available water capacity based on standard soil profiles; it does not account for changes in root architecture driven by successive drought stress. If root systems deepened significantly in 2025 and then again in 2026, trees entering spring 2027 may extract soil moisture more efficiently than baseline MORECS assumptions predict — meaning soils could dry faster next season, even under average spring conditions, if autumn 2026 recharge remains incomplete. This remains a hypothesis. Its practical implication for claims exposure — if borne out — would be elevated SMD trajectory in spring 2027 relative to seasons following a single drought year.
The practical signal to watch: weekly SMD progression in April–May 2027. If SMD rises faster than the 2022 or 2025 analogues in the early growing season — before cumulative sunshine hours would ordinarily account for it — that would be consistent with the compounding hypothesis. Monitoring should begin from the first MORECS data release of spring 2027.
Sources: ABI "Sinking UK" press release (21 Mar 2023); ABI written evidence to House of Lords Environment and Climate Change Committee (Nov 2025); ABI Q2 2026 property claims data (3 Aug 2026); Insurance Times. All figures are directly published by the ABI unless stated.
| Year / Period | ABI claims | Total payout | Avg claim |
|---|---|---|---|
| 2022 (full year) | 23,000 total 18,000 in H2 — 1 every 15 mins |
£219m | £9,600 |
| H1 2025 | ~9,000 households | £153m | £17,264 |
| 2025 (full year) | — | £307m (record) | — |
| Q2 2026 (Apr–Jun only) | — | £72m | £20,000 (record) |
The Q2 2026 ABI data (published 3 Aug 2026) covers April to June — before either Geobear risk threshold was crossed and before the bulk of the summer heatwave season. The £72m payout and £20,000 average are therefore pre-peak figures.
The headline numbers from earlier surge years (2003: ~55,000 claims; 2006: ~40,000+) appear higher than 2022 (23,000) despite comparable or more severe ground conditions. Several structural factors explain this:
After each surge year, insurers raise subsidence excesses, tighten acceptance criteria and in some cases add natural peril exclusions. Many homeowners discover the gap only when they try to claim.
Around 7 in 10 UK properties are estimated to carry only ~66% of the cover needed for a full rebuild. Underinsured properties generate lower-value claims or none at all.
Fewer claims does not mean lower total cost. Average claims rose from £9,600 in 2022 to £17,264 in H1 2025 to £20,000 in Q2 2026 — a near-tripling in four years driven by construction inflation and more complex damage.
Three surge years in eight (2018, 2022, 2025) mean ground damaged in 2025 had not recovered before 2026 began — a compounding dynamic that is extending claim lifecycles and complicating loss adjustment.
| Year | Profile | First above 218mm | First above 320mm | Peak SMD | Notes |
|---|
Sources: NOAA CPC Oct 2026 advisory; elninolive.com weekly tracker (28 Oct 2026); Met Office autumn/winter 2026–27 outlook; WMO multi-model ensemble Oct 2026.
| Layer | Signal type | Current status |
|---|---|---|
| ENSO / El Niño | Global context signal | 28 Oct: Niño 3.4 +3.4°C — approaching 1997/98 record (~+3.6°C). 83%+ historic event OND 2026. Met Office: wetter/stormier UK winter increasingly likely. |
| North Atlantic Oscillation | Jet stream / blocking driver | Atlantic pattern now firmly established. 63.4mm wk to 27 Oct. Met Office: increasingly unsettled Nov–Dec. Recharge active. |
| UK pressure pattern | Regional driver | EA Gold Command still active. Blocking broken down. UK temp record 16.5°C. River levels and groundwater still depleted. |
| MORECS SMD | Ground condition evidence | 283.5mm (3 Nov) — below 320mm for first time since 8 Jul. 63.4mm wk to 27 Oct dropped SMD 47.9mm. Recovery confirmed; sustained 20mm+/wk still required. |
| Case reports | Impact validation | 2022 rose from 18 Jul. 2025 from 11 Aug. 2026 active monitoring. |
London used as a proxy for clay-rich South East England.
A surge-risk hypothesis strengthens only when multiple signals align and MORECS confirms ground drying.
Learn more: What is subsidence?
Last updated: · MORECS week ending:
Sources: MORECS Square 161 weekly data (Met Office Hadley Centre), Met Office UK weather summaries and ENSO commentary, NOAA Climate Prediction Center, WMO El Niño/La Niña Update (2 Jun 2026), Geobear internal subsidence case report trends.
This dashboard is an operational early-warning framework, not a property-level diagnosis. It should not be used as a basis for insurance or engineering decisions without professional assessment.
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