Clay shrink-swell risk (global)
This layer maps the global risk of clay shrink-swell, the behaviour of expansive soils that swell when wet and shrink when dry.
Category: Physical risks · Mitigating services · Geological Coverage: Global Format: Raster grid (~1 km) Used in risk analysis: Yes — gates Mitigating services
What it shows
This layer maps the global risk of clay shrink-swell, the behaviour of expansive soils that swell when wet and shrink when dry. These ground movements can damage buildings, roads and other infrastructure. The layer offers a worldwide screening view of where expansive-soil hazard is most likely, helping flag sites where ground stability deserves closer attention.
How it is built
Where precise national hazard or soil maps exist, they are used directly — including France, Spain, the United Kingdom, the Netherlands, Norway, the United States, Brazil and Canada. Elsewhere, a calibrated proxy fills the gaps, built from a decision rule on global soil properties (clay content, cation-exchange capacity and the probability of expansive Vertisol soils). The proxy was trained on the French, Spanish and UK national hazard maps (matching the exact class in 58% of cases and within one class in 94%) and validated against global Vertisol references in the tropics. National areas appear fine-grained while proxy areas are coarser at roughly a 1 km grid. This is a screening layer, not a siting tool.
How to read it
Values fall into three classes: 1 Low, 2 Medium and 3 High. Higher classes indicate greater susceptibility to expansive-soil ground movement. National-map areas are more detailed than proxy areas; treat the proxy regions as indicative.
Source
BRGM, IGME, BGS, BRO, NGU, UC Davis, IBGE, AAFC and ISRIC SoilGrids (CC-BY).
Comparison with the WWF Risk Filter Suite
There is no equivalent indicator in the WWF Risk Filter Suite. Clay shrink-swell is a geophysical ground hazard rather than a biodiversity or water risk, so it falls outside the WWF methodology and is a Darwin extension.
Risk analysis
A site is flagged on a dimension by combining a proximity trigger (this layer) with an activity trigger (the entity's ENCORE pressure/service). Proximity only → Potentially material; proximity and the matching ENCORE pressure/service is material → Very material; neither → Not material.
| Dimension | ENCORE service / pressure | Proximity trigger (this layer) | Activity trigger (entity) |
|---|---|---|---|
| Mitigating services | Clay shrink-swell | Layer value above 3 | — |
Legend
Symbolised field: Shrink-swell risk
| Class | Colour |
|---|---|
| Low | #fee08b |
| Medium | #fc8d59 |
| High | #d73027 |
Generated from darwin/layers/layer-clay-shrink-swell-global.toml and risk_indicator_pairs.toml (develop).