OR/18/006 GeoClimate Basic: 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 as the risk of loss has been mitigated as a result of the design of the property.

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

Scale

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

Attribute table field decriptions

Table 1    Basic product attributes.
Field Name Field Description
CLASS Classification of hazard using values:- Improbable, Possible, Probable, Unavailable
LEGEND Description of hazard
VERSION Dataset name and version number

Creation of the dataset

GeoClimate combines and interprets data on shrink-swell hazard susceptibility, BGS groundwater model and UKCP09 climate change projections, to project future shrink-swell hazard (Figure 1). A robust methodology has been developed by expert BGS Geological Engineers, Groundwater Geologists and GIS specialists. The source datasets utilised in the development of GeoClimate: Shrink-Swell are:

  • BGS GeoSure Subsidence: BGS GB dataset providing geological information on natural ground instability, 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: The UKCP09 medium emissions scenario was used to force the 11 Regional Climate Model simulations, providing absolute values provided as continuous daily projections from 1950 to 2099.

In addition, further research is incorporated including:

  • A Days in Drought (DiD) value, calculated from the ZOODRM groundwater model and 11RCM projections,
  • Modified Plasticity Index (IP') values, extracted from the BGS GeoSure Shrink-Swell layer. The output is a GeoClimate Volume Change Potential (VCP) score

GeoClimate Basic is derived from the same methodology as GeoClimate Premium, and is a lower resolution summary product, providing information on the average climate change scenario and the highest susceptibility GeoSure shrink-swell value within the 2 km grid cell.

Table 1 shows the product attributes. Table 2 shows the ratings for GeoClimate Basic 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 2    GeoClimate Basic VCP ratings, showing the effect
of projected climate change on clay shrink-swell susceptibility.

GeoSure Modified Plasticity Index (IP') Value

<10

10–20

20–40

40–60

>60

Score

A

B

C

D

E

Days
in
Drought
(DiD)

<100

1

A1
Improbable
change

B1
Improbable
change

C1
Improbable
change

D1
Improbable
change

E1
Improbable
change

100–115

2

A2
Improbable
change

B2
Improbable
change

C2
Improbable
change

D2
Improbable
change

E2
Improbable
change

115–130

3

A3
Improbable
change

B3
Improbable
change

C3
Improbable
change

D3
Possible
increase

E3
Possible
increase

130–145

4

A4
Improbable
change

B4
Improbable
change

C4
Possible
increase

D4
Probable
increase

E4
Probable
increase

>145

5

A5
Improbable
change

B5
Possible
increase

C5
Possible
increase

D5
Probable
increase

E5
Probable
increase

Example Score Interpretation: The GeoClimate Basic rating for the area of interest is Probable (Red) in the 2050 projection. This shows that it is probable that the likelihood of clay shrink-swell occurring in this area, causing subsidence in low-rise buildings, will increase due to changes in climate, by 2050.

For all GeoClimate Basic results, the rating provided is the highest Geoclimate value within the selected 2 km pixel. For a more precise rating, please consult the GeoClimate Premium product (see GeoClimate Premium: technical information).

Table 3    GeoClimate Basic colours and susceptibility text.
Colour (used in legend) Associated susceptibility description
Blue It is ‘improbable’ that foundations will be affected by increased clay shrink-swell due to climate change.
Yellow It is ‘possible’ that foundations will be affected by increased clay shrink-swell due to climate change.
Red It is ‘probable’ that foundations will be affected by increased clay shrink-swell due to climate change.
Grey Input datasets are unavailable.

The susceptibility ratings (Table 3) colour scheme is colour-blind safe.

Temporal scale

For the GeoClimate Basic suite of layers, a susceptibility score is provided for the following 11-year time periods:

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

Coverage

The GeoClimate products are national scale datasets covering Great Britain. The extent of the GeoClimate Basic shrink-swell suite of datasets, is shown in Figure 1.

Figure 1    Coverage of GeoClimate Basic.

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.