OR/18/006 GeoClimate Premium: technical information

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Harrison, A, Jones, L, Entwisle, D, Hulbert, A, Lark, M, Mansour, M, Richardson, J, Wang, L, and White, J. 2018. User guide for the British Geological Survey GeoClimate: clay shrink-swell dataset. British Geological Survey. (OR/18/006).

Definitions

Hazard: A potentially damaging event or phenomenon.
Risk: The impact of the hazard on people, property or capital.
For example, a shrinkable clay could be perceived as a hazard, but the likelihood of it causing structural damage would be the risk.

A high hazard does not necessarily translate to a high risk. For example, if a particular location has a relatively high ground stability hazard, but the properties that are built there have taken this into account, and are designed to withstand the hazard, they will not have a comparable level of risk. This is because the likelihood of the hazard causing any loss has been reduced due to the design of the property.

GeoClimate does not identify the cost of a hazard being realised, and therefore does not consider risk. GeoClimate only examines the conditions that leave an area exposed to a hazard and the change in potential due to climatic changes.

Scale

The GeoClimate dataset is produced for use at 1:50 000 scale providing 50 m ground resolution.

Attribute table field decriptions

Table 4    Premium product attributes.
Field Name Field Description
CLASS Classification of hazard using values:- Highly Unlikely, Unlikely, Likely, Highly Likely, Extremely Likely
LEGEND Description of hazard
VERSION Dataset name and version number

Creation of the dataset

GeoClimate combines current GB subsidence hazard susceptibility, a GB groundwater model and climate change projections, to project future subsidence hazard (Figure 1). Expert BGS Geological Engineers, Groundwater Geologists and GIS specialists collaborated to generate a robust methodology. The datasets utilised and combined in GeoClimate are:

  • BGS GeoSure Subsidence: BGS GB dataset providing geological information on potential subsidence, providing 5 classes from Hazard Rating A (pre-dominantly non-plastic ground conditions) to Hazard Rating E (predominantly very high plasticity ground conditions).
  • Zooming Object Oriented Distributed Recharge (ZOODRM) model: Provides gridded daily soil moisture deficit (SMD) values for UK, based on inputted rainfall and surface values.
  • 11 RCM UKCP09 climate models: UKCP09 medium emissions scenario was used to force the 11 Regional Climate Model simulations, providing absolute values to input into GeoClimate. The values provided are continuous daily projections from 1950 to 2099.

These datasets are used to produce a GeoClimate Volume Change Potential (VCP) score, which is based on:

  • Modified Plasticity Index (IP’) values, extracted from the BGS GeoSure Shrink-Swell layer,
  • A Days in Drought (DiD) value, calculated from the ZOODRM groundwater model and 11RCM projections.

Table 5 shows the product attributes. Table 6 shows the ratings for the Premium product.

The GeoSure Shrink-Swell rating does not change for a geological deposit. However, the projected changes in climate vary across GB, and therefore the GeoSure shrink-swell rating letter is combined with a number that represents the days in drought projected for that area.

Table 5    GeoClimate Premium: VCP ratings, showing the effect
of projected climate change on clay shrink-swell susceptibility.

GeoSure IP' Value

<10

10–20

20–40

40–60

>60

Score

A

B

C

D

E

Days
in
Drought

<100

1

A1
No effect

B1
No effect

C1
No effect

D1
No effect

E1
No effect

100–115

2

A2
No effect

B2
No effect

C2
No effect

D2
No effect

E2
No effect

115–130

3

A3
No effect

B3
No effect

C3
No effect

D3
Small effect

E3
Small effect

130–145

4

A4
No effect

B4
No effect

C4
Small effect

D4
Noticeable effect

E4
Noticeable effect

>145

5

A5
No effect

B5
No effect
except if external changes occur

C5
Small effect

D5
Major effect

E5
Major effect

Table 6    GeoClimate Premium colours and legend descriptions.
Colour (used in legend) Associated susceptibility description
Blue It is ‘highly unlikely’ that foundations will be affected by increased clay shrink-swell due to climate change.
Light Blue It is ‘unlikely’ that foundations will be affected by increased clay shrink-swell due to climate change.
Yellow It is ‘likely’ that foundations will be affected by increased clay shrink-swell due to climate change.
Orange It is ‘highly likely’ that foundations will be affected by increased clay shrink-swell due to climate change.
Red It is ‘extremely unlikely’ that foundations will be affected by increased clay shrink-swell due to climate change.
Grey Input datasets are unavailable.

N.B. When it is ‘unlikely’ that foundations will be affected by increased clay shrink-swell due to climate change, unless external changes occur, examples of external changes include planting or removal of trees near the building or drainage changes.

The susceptibility ratings (Table 7) colour scheme is colour-blind safe.

Temporal scale

For the GeoClimate Premium suite of layers, 3 layers are provided for the following 11-year time periods:

  • 2020 (2015 to 2025)
  • 2030 (2025 to 2035)
  • 2040 (2035 to 2045)
  • 2050 (2045 to 2055)
  • 2080 (2075 to 2085)

The 3 layers provided for each time period are:

  • Average (median average period of dry conditions)
  • Drier (longest period of dry conditions)
  • Wetter (shortest period of dry conditions)

Coverage

The GeoClimate products are national scale datasets covering Great Britain. The extent of the GeoClimate Premium shrink-swell layer is shown in Figure 2.

Figure 2    Coverage of GeoClimate Premium.

Data format

The GeoClimate dataset has been created as vector polygons and is available in a range of GIS formats, including ArcGIS (.shp), ArcInfo Coverages and MapInfo (.tab). More specialised formats may be available but may incur additional processing costs.

Limitations

  • The GeoClimate dataset has been developed at 1:50 000 scale and must not be used at larger scales.
  • GeoClimate is concerned with potential ground stability related to NATURAL shrink-swell geological conditions only.
  • GeoClimate is based on, and limited to, an interpretation of the records in the possession of The British Geological Survey at the time the dataset was created.
  • An indication of natural ground movement due to shrink-swell does not necessarily mean that a location will be affected by ground movement or subsidence. Such an assessment can only be made by inspection of the area by a qualified professional.