Risk/opportunity:(from the Climate Change Risk Assessment for Scotland 2012):
FL8a Roads at significant risk of flooding TR1 Risk of traffic disruption
SCCAP theme: Buildings and infrastructure Society
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
January 2014 to March 2015: Flood Incidents recorded on the trunk road network:
- Total number: 567
- 51.7% were on sections of the network within Potentially Vulnerable Areas (PVAs) as identified in SEPA’S National Flood Risk Assessment (NFRA)
- A small proportion of incidents (8, or 1.41%) resulted in full road closure
- Around one sixth (16.75%) resulted in flood depths of 3cm or more
Flooding was the fourth most common cause of trunk road incidents – behind abandoned or broken down vehicles, road traffic collisions and damaged road or street furniture. Flooding was the most common cause of weather-related incidents and the most common cause of road closures.
Flooding was the fourth most common recorded cause of trunk road incidents between January 2014 and March 2015
Climate change is predicted to increase the frequency and extent of flood events and impacts
Only a small proportion of recorded flood events during the period assessed were severe enough to result in full road closure
Approximately half of the recorded flood events during the period assessed were located within National Flood Risk Assessment (NFRA) Potentially Vulnerable Areas (PVAs)
Flooding can disrupt the operation of the road network with knock-on consequences for many social and economic functions – e.g. delaying deliveries, preventing or delaying people from accessing employment or disrupting vital healthcare services. Communities located in remote areas are particularly vulnerable to road network disruption as they rely more heavily on road transport than those living and working in other parts of Scotland and alternative routes (where these exist) often require long diversions.
This indicator uses standardised trunk road incident data as reported by Scotland’s trunk road Operating Companies (OCs) to assess flood 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 below, IRIS has only been fully operational since August 2014 meaning that the data presented in this section is incomplete (i.e. there are likely to be more flooding incidents than are reported here).
Table 1 presents current figures for each of the four metrics assessed for this indicator for the period January 2014 – March 2015. The location of all recorded trunk road flooding incidents during this period is shown in Figure 1.
Table 1 Trunk road network flood incidents (Jan 2014 – Mar 2015)
BT4a: Total number of reported trunk road flooding incidents
BT4b: Proportion of reported trunk road flooding incidents located within Potentially Vulnerable Area (PVAs)
BT4c: Proportion of reported trunk road flooding incidents resulting in road closure
BT4d: Proportion of reported trunk road flooding incidents where flooding is over 3cm depth
Potentially Vulnerable Areas (PVAs), as identified in the National Flood Risk Assessment (SEPA, 2011), are locations where flood hazards could affect multiple receptors and therefore where the consequences of flooding are likely to be high. Flooding events on transport links within such areas are likely to have important knock-on consequences for other socio-economic systems. In this respect it should be noted that just under half (48.7%) of the trunk road network itself is located within the PVAs, and that just over half (51.68%) of the trunk road flooding incidents recorded were located within PVAs. The spatial distribution of PVAs and trunk road flooding incidents within the PVAs is shown in Figure 1.
Figure 1. Location of all recorded trunk road flooding incidents (LH map) and all of those located within Potentially Vulnerable Areas (RH map) between January 2014 and March 2015 (IRIS, SEPA (2011)).
In terms of the severity of impact, only 1.41% of trunk road flooding incidents resulted in full road closure. The location of these incidents is shown in Figure 2.
Flooding of over 3cm depth provides another proxy assessment of flood incident severity (see Appendix 1, Table 4 Indicator Methodology below). 16.75% of trunk road flooding incidents recorded during the period assessed were incidents where flood depth was over 3cm. The location of these incidents is also shown on Figure 2.
To put these metrics in context, Table 2 summarises the number of different types of reported trunk road incidents and the proportion of incidents which resulted in a road closure. Flooding was the fourth most common type of incident overall and occurred more frequently than other incident types directly associated with climate change risk, namely high winds, landslides and severe weather. Also, the number of flooding incidents resulting in a complete road closure occurred more frequently but with the same order of magnitude as road closures associated with other potential climate change risks, i.e. high winds, landslides and severe weather.
Figure 2 Location of trunk road flooding incidents that resulted in road closure (LH map) and those incidents where flooding was over 3cm depth (RH map) between January 2014 and March 2015
Table 2 Comparison of trunk road network incidents January 2014 – March 2015
Total number of reported incidents
Incidents resulting in road closure (% in brackets)
Abandoned or broken down vehicles
Road traffic collisions (RTC)
Damaged road / street furniture
Landscaping and fallen / overhanging branches
Obstruction or damage from vandalism
Severe weather (snow, fog and rain)
Note: Incidents have been listed in order of frequency of occurrence, highest to lowest.
 According to the approach taken by NFRA, trunk roads were regarded as high value receptors and hence the presence of a trunk road increases the likelihood of an area being designated a PVA
Historic flooding incident data is not available prior January 2014 to assess these metrics over time (i.e. to determine any trends in flood events affecting the trunk road network). 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 (i.e. risk of traffic disruption as a result of flooding). Overall there is a clear upward trend in winter precipitation as well as increasing heavy rainfall in winter (Sniffer, 2014). It is expected that these climatic changes will have contributed to increased frequency and extent of pluvial and fluvial source flooding 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) assessed changes in flood risk to road infrastructure as a result of anticipated climate changes. Whilst this assessment was only undertaken for England and Wales (due to data availability) it provides a broad indication of what might happen in Scotland in the future given anticipated climate changes. Given this, transport specific aspects from the UK CCRA can be used in conjunction with general aspects from the Scotland CCRA (HR Wallingford et al, 2012b) to understand how flooding related impacts to road infrastructure might change in the future.
The following projected changes are anticipated for the future:
- The proportion of the road network located in areas at risk of flooding is projected to increase
- Road infrastructure that is already located in the floodplain is expected to be affected by flooding more frequently
- Increased incidence of intense summer rainfall events may result in more frequent pluvial (surface water) flooding
The last two projected changes are of particular relevance. Any increase in the frequency of flood events affecting the road network (fluvial, pluvial or coastal) may also increase the number of flooding related incidents on the trunk road network recorded and managed by the OCs. Crucially, any flooding incident recorded by the OCs (with the exception of minor incidents perhaps) is likely to be of a severity such that it causes significant traffic disruption (Transport Scotland, undated). In summary therefore, anticipated climate changes are likely to increase the number of flooding incidents on the trunk road network and increase traffic disruption ( though note that this does not account for any action that might be taken, such as increasing drainage capacity).
 Indicator BT2 provides a detailed description of the assessment undertaken.
The limitations to the assessment of this indicator are summarised below:
- Transport Scotland’s Integrated Road Information System (IRIS) has only been fully operational since August 2014. In particular, IRIS has been collecting OC data for the west of the country since late 2013 but only since August 2014 for the east (Ramage, 2015). As such, the assessment presented here is based on incomplete data and the number of flood events affecting the road network will be higher than that recorded. Also, it will not be possible to draw any conclusions as to the spatial distribution of flood events (e.g. to account for possible variations in climate and associated climate impacts between west and east Scotland).
- Some trunk roads are not covered under IRIS as they are not managed by the OCs (Ramage, 2015). This will also affect the accuracy of this indicator’s metrics but the number of flood events affecting the trunk road network is likely to be higher in reality as a result.
- Some major bridges which connect parts of the trunk road network were managed by separate statutory authorities during the period of assessment and thus did not form part of the trunk road network. Bridge closures due to high winds were not included in the IRIS data.
- Some data recording is not mandatory for the OCs 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 as part of this indicator may not be consistent.
- The projections of what might happen in the future in terms of flood events affecting the road network are based on English and Welsh data only from the UK CCRA. Whilst this provides a useful broad indication of possible future risks, the accuracy of any quantitative assessment is limited and the ‘future risk assessment’ / trends assessment is based on climate projections data only, as per the Scotland CCRA.
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)
SEPA (undated). Flood Risk Management (Scotland) Act 2009 – Appraisal Method for Flood Risk Management Strategies. [not available online]
SEPA (2011). The National Flood Risk Assessment [online]. Available at: http://www.sepa.org.uk/environment/water/flooding/flood-risk-management/national-flood-risk-assessment/ [accessed 27/05/15]
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]
Thornes, J., Rennie, M., Marsden, H., & Chapman L (2012). Climate Change Risk Assessment for the Transport Sector [online]. Available at: https://www.gov.uk/government/publications/uk-climate-change-risk-assessment-government-report [accessed 22/05/15]
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]
The analysis and development of this indicator was undertaken by Dr Neil Ferguson (University of Strathclyde) and Dr Peter Phillips (Collingwood Environmental Planning Limited), utilising National Flood Risk Assessment Potentially Vulnerable Area (PVA) data provided by SEPA and trunk road incident data provided by Transport Scotland.
Katherine Beckmann, Heriot-Watt University / CXC contributed to this indicator.