Risk/opportunity:(from the Climate Change Risk Assessment for Scotland 2012):
R2 Landslide risks on the road network

Narratives: Extreme weather and infrastructure

SCCAP theme: Buildings and infrastructure

SCCAP objectives:
B1: Understand the effects of climate change and their impacts on building and infrastructure networks
B2: Provide the knowledge, skills and tools to manage climate change impacts on buildings and infrastructure
B3: Increase resilience of buildings and infrastructure networks to sustain and enhance the benefits and services provided

Latest figures

Landslide incidents recorded on the trunk road network

between January 2014 and March 2015

No.

%

Total number of trunk road landslide incidents

12

-

Number of these incidents resulting in road closure

5

42%

Number of these incidents located within very remote rural areas

7

58%

Trend
At a glance
  • Climate change predictions suggest that landslide risk to the trunk road network in Scotland is likely to increase
  • Landslide events affecting the trunk road network are much less frequent than flooding events
  • Almost half of the recorded landslide events resulted in full road closure
  • Over half of the recorded landslide events were located within very remote rural parts of Scotland which are particularly vulnerable to loss of road network connectivity

Transport is a means to an end supporting many different social and economic functions. Landslide incidents affecting road infrastructure can cause disruption to road transport with knock-on consequences for these functions, such as delaying deliveries, preventing or delaying people from accessing employment, disrupting vital healthcare services. Climate change predictions suggest that there will be an elevated risk of landslides to the trunk road network in Scotland due to the detrimental effect of increased rainfall on slope stability[1]. Tracking this indicator will show whether these predictions are realised on the ground as well as revealing any spatial patterns in the impacts.

This indicator utilises standardised trunk road incident data reported by Scotland’s Trunk Road Operating Companies (TROCs), to assess landslide events affecting the road network.  The data is managed centrally by Transport Scotland through the Integrated Road Information System (IRIS). As explained further in the limitations section, IRIS has only been fully operational since August 2014 meaning that the data presented in this section is incomplete (i.e. there may be more landslide incidents than are reported here).

Related Indicators:

BT4 Flood events affecting the trunk road network


[1] The total distance of road at risk will not increase indefinitely. Landslide risks to the road network require a susceptible slope above or adjacent to a road and such conditions are limited (Thornes et al, 2012).

Table 1 presents current figures for landslide impacts on trunk roads.

Table 1 Trunk road network landslide incidents (January 2014 – March 2015)

Metrics

No.

%

BT22: Total number of trunk road landslide incidents

12

-

BT23: No. of trunk road landslide incidents resulting in road closure

5

42%

BT22b: No. of trunk road landslide incidents located in very remote rural areas

7

58%

Landslide incidents on the trunk road network are a much less frequent occurrence than floodingincidents.  During the same period some 567 flooding incidents were reported compared to only 12 landslides (see indicator BT4).  It may be the case that the prerequisite conditions for landslide are less common than the prerequisites for flooding. Furthermore, flooding can result from many sources.

Figure 1 Location of all recorded trunk road landslide incidents (LH map); all recorded trunk road landslide incidents resulting in road closure (centre map); and all recorded trunk road landslide incidents located within very remote rural areas (RH map) between January 2014 and March 2015

Spatial data for the various landslide metrics are shown in Figure 1.  Almost half of the recorded trunk road landslide incidents (5 out of 12 or 42%) recorded during the period assessed resulted in full road closure – clearly causing a more severe impact than those that do not cause a full closure.

The true cost of landslide events to the road network are often associated with the socio-economic impacts caused by the severance of access to or from relatively remote communities (Winter et al, 2013). In this context it is important to note that more than half of the recorded trunk road landslide incidents (7 of 12 or 58%) were located within very remote rural parts of Scotland.

Most of the trunk road landslide incidents recorded were in the west of the country (see Figure 1). This could, in part, be a function of the IRIS data made available by Transport Scotland as the dataset is more complete for the west of the country (see the Limitations section). However, these findings mirror the findings of an assessment of landslide hazard and risks on the Scottish road network undertaken in 2013, which found that sites with the highest hazard ranking score (greatest susceptibility) were located primarily on the west of the country (ibid). Both of these findings make sense given that landslide risks and impacts to roads require a susceptible slope above or adjacent to a road (Thornes et al, 2012). In Scotland these conditions occur most frequently on the more mountainous west side of the country.

Historic trunk road landslide incident data is not available prior to January 2014. However, historic climate data shows how key aspects of climate (rainfall) have changed leading to impacts on biophysical systems (e.g. hydrological response of Scotland’s catchments and watercourses) and ultimately changes to the scale and magnitude of relevant climate risks (e.g. landslide risks to the road network). Overall there is a clear upward trend in winter precipitation as well as increasing heavy rainfall in winter (Sniffer, 2014). Although there is no direct link between increased winter precipitation and landslide risk, the UK Climate Change Risk Assessment (CCRA) makes an assumption that increases in average winter precipitation will result in increased risk (likelihood) of landslide (Thornes et al, 2012). In this regard, it is expected that these climatic changes (Sniffer, 2014) may have contributed to increased frequency of landslide events and associated impacts on the trunk road network. A fuller account of historic climate trends is provided in indicator BT2.

The UK Climate Change Risk Assessment (HR Wallingford et al, 2012a; Thornes et al, 2012) undertook a qualitative assessment of changes in landslide risk to road infrastructure as a result of anticipated climate changes. This included a Scotland specific assessment. The Scotland assessment considered trunk roads only and found that in all climate change (emissions) scenarios, the length of the trunk road network likely to be impacted by landslide in a year would double from the current extent by the 2080s at the latest (for medium and high emissions scenarios this increase may take place by the 2050s). This equates to an increase from 125km/year at risk today (2012) to 250km/year by 2080. It should be noted however that the total length of road at risk cannot increase indefinitely as there has to be a susceptible slope adjacent to or above the road (Thornes et al, 2012; Winter et al, 2013). Clearly these conditions are not met everywhere so there will only ever be a limited number of sites at risk of landslide.

It should be noted that any landslide incident recorded by the TROCs is likely to be of a severity such that it causes serious traffic disruption[1](Transport Scotland, undated). In summary therefore, anticipated climate changes are likely to increase the number of landslide incidents on the trunk road network and increase traffic disruption (notwithstanding the moderating effect that preventative actions, such as increasing drainage capacity, may have).


[1] A possible exception is Transport Scotland’s category ‘Minor Incidents’ (see Methodology section).

There are several key limitations to the BT22 and BT23 assessments as summarised below:

  1. Transport Scotland’s Integrated Road Information System (IRIS) has only been fully operational since August 2014. In particular, IRIS has been collecting TROC data for the west of the country since late 2013 but only since August 2014 for the east (Ramage, 2015). As such, the BT22/23 assessment presented here is based on incomplete data and the number of landslide events affecting the road network may be higher than that recorded. Also, it will not be possible to draw robust conclusions as to the spatial distribution of landslide events (e.g. to account for possible variations in climate and associated climate impacts between west and east Scotland).
  2. Some trunk roads are not covered under IRIS as they are not managed by the TROCs (Ramage, 2015). This will also affect the accuracy of the metrics – i.e. the number of landslide events affecting the trunk road network could be higher in reality as a result.
  3. Some data recording is not mandatory for the TROCs and the consistency of data recording year-to-year may change (Ramage, 2015), especially given the somewhat qualitative nature of the trunk road incident classification system (Traffic Scotland, undated). As a result, the accuracy of the absolute figures / metrics assessed may not be consistent.

The data on number and location of landslide incidents used could be seen to paint an overly simplistic picture of landslide impacts to the trunk road network. As Winter et al (2013) point out, the real impacts of landslide related disruption are caused by the severance of access to or from relatively remote communities. Given this, it would be useful for future iterations of this indicator to access data on the duration of road closure (complete or partial) as well as annual average daily traffic (AADT) on the road link affected. This data would provide a fuller picture of the severity of disruption and the possible implications for affected communities.

Edmond, G. (2015). Personal communication with Graham Edmond, Transport Scotland Head of Network Maintenance, March 6, 2015

HR Wallingford, AMEC Environment and Infrastructure, The Met Office, Collingwood Environmental Planning, Alexander Ballard Ltd, Paul Watkiss Associates, & Metroeconomica (2012a). UK Climate Change Risk Assessment [online]. Available at: https://www.gov.uk/government/publications/uk-climate-change-risk-assessment-government-report [accessed 22/05/15]

HR Wallingford, AMEC Environment and Infrastructure, The Met Office, Collingwood Environmental Planning, Alexander Ballard Ltd, Paul Watkiss Associates, & Metroeconomica (2012b). A Climate Change Risk Assessment for Scotland [online]. Available at: https://www.gov.uk/government/publications/uk-climate-change-risk-assessment-government-report[accessed 22/05/15]

Ramage, A. (2015). Personal communication with Alex Ramage, Transport Scotland Head of Management Information Systems, April 23, 2015

Scottish Government (2014). Scottish Government Urban / Rural Classification [online]. Available at: http://www.gov.scot/Resource/0046/00464780.pdf [accessed 21/05/15]

SEPA (undated). Flood Risk Management (Scotland) Act 2009 – National Flood Risk Assessment Methodology [online]. Available at: http://www.sepa.org.uk/media/99914/nfra_method_v2.pdf[accessed 21/05/15]

Sniffer (2014). Scotland’s Climate Trends Handbook [online]. Available at: http://www.environment.scotland.gov.uk/climate_trends_handbook/index.html [accessed 21/05/15]

Transport Scotland (undated). 4th Generation Term Contract for Management and Maintenance of the Scottish Trunk Road Network North East Unit [online]. Available at: http://www.transportscotland.gov.uk/system/files/documents/tsc-basic-pages/NE%20-%20S7P3.pdf[accessed 27/05/15]

Transport Scotland (2015). Operating Companies pages [online]. Available at: http://www.transportscotland.gov.uk/road/maintenance/operating-companies [accessed 27/05/15]

Winter, M.G., Harrison, M., Macgregor, F., and Shackman, L. (2013). Landslide hazard and risk assessment on the Scottish road network. Geotechnical Engineering, Vol.166, pp.522-539

ClimateXChange (2016) Adaptation to Climate Change: Context and Overview for Transport Infrastructure Indicators. Available online at  our Indicators and trends page 

The analysis and development of Indicators BT22 / BT23 was undertaken by Dr Neil Ferguson (University of Strathclyde) and Dr Peter Phillips (Collingwood Environmental Planning Limited).

Katherine Beckmann, Heriot-Watt University / CXC contributed to this indicator.

Transport Scotland provided the trunk road incident data that underpinned this assessment.