Risk/opportunity:(from the Climate Change Risk Assessment for Scotland 2012):
FL8b Railways at significant risk of flooding
Narratives: Flooding and infrastructure
SCCAP theme: Buildings and infrastructure
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
BT8a: Percentage of rail network at risk of fluvial flooding
BT8b: Percentage of rail network at risk of pluvial flooding
BT8c: Percentage of rail network at risk of coastal flooding
Note: All the above metrics are based on 0.5% probability (1:200 year) flood events
- Scotland’s rail network is at risk of flooding from fluvial, pluvial and coastal sources
- Climate change predictions suggest that flooding of rail infrastructure in Scotland will become more extensive and more frequent
- Flood risks to rail infrastructure are spread across the Scottish rail network and the greatest flood risk is posed by pluvial source flooding
- Only small sections of Scotland’s rail network are exposed to fluvial and coastal flood risk
Transport supports many social and economic functions. In 2013/14, 86.3 million passenger journeys were made by rail in Scotland which represents 16% of all public transport journeys. Rail patronage has increased by 35% since 2004/05 and constitutes a growing share of public transport journeys. In contrast, there has been a decline of 8.2% in the amount of freight (tonnes) lifted by rail between 2002/03 and 2012/13. The modal share of freight (in tonne-km) carried by rail in Scotland in 2010 was 7% (Transport Scotland, 2014).
Flooding of rail infrastructure can cause disruption to rail transport with knock-on consequences for these functions – e.g. preventing or delaying people accessing work, delaying rail freight etc. Climate change predictions suggest that flooding of rail infrastructure will become more extensive and more frequent.
Current figures for each of the three metrics are presented in Table 1 and Figure 1. The location of flood risk to the rail network is shown on Figure 2.
BT8a: Proportion of rail network at risk of fluvial flooding (%)
BT8b: Proportion of rail network at risk of pluvial flooding (%)
BT8c: Proportion of rail network at risk of coastal flooding (%)
Table 1 Proportion of rail network at risk of flooding (1:200 year event)
Figure 1 Proportion of rail network at risk of flooding (1:200 year event)
Table 1 and Figure 1 show the extent to which the rail network is exposed to various flood sources. The degree of exposure varies between flooding source – e.g. 8.41% of the network is exposed to pluvial flooding compared to only 0.61% for coastal.
Figure 2 shows how flood risks to the rail network are spread across Scotland reflecting the spatial distribution of watercourses and their catchments (fluvial flood risk), impermeable features or areas with poor surface water drainage provision (pluvial flood risk) and low lying coastal areas (coastal flood risk). It should be noted that areas of fluvial, pluvial and coastal source flood risk coincide on certain lengths of the rail network which means that that the proportion of the network at risk from any form of flooding is less than the combined percentages from the individual flooding sources.
Figure 2 Rail network at risk of flooding (1:200 year flood event) – spatial distribution of fluvial, pluvial and coastal source flood risk to the rail network in Scotland
Historic flood hazard and rail network data is not available to assess these metrics over time. 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 rail network 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 rail network.
 A fuller account of historic climate trends is provided in indicator BT2 (Risk of road closures from flooding).
The UK Climate Change Risk Assessment (HR Wallingford et al, 2012a; Thornes et al, 2012) assessed changes in flood risk to rail 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. As such, 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 rail infrastructure might change in the future.
The CCRA for England and Wales indicated that the projected length of railway at significant likelihood of flooding (where significant is defined as a 1.3% annual probability) would be between 2,000km and 2,600km by 2020 compared with a baseline of about 2,000km (Thornes et al, 2012). This equates to a possible increase of between 0% and 30% with the range reflecting the different climate change (emissions) scenarios considered in the assessment. The CCRA also highlighted how in addition to an increase in the overall length of infrastructure that could be affected, the frequency of flooding of infrastructure that is already located in the floodplain is expected to increase (ibid). These projections do not account for actions taken to alleviate flood risk to railways (e.g. flood defence infrastructure, enhanced maintenance regimes and so on (see indicator BT6)) which may help to reduce overall flood risk. Whilst these projections are focussed on England and Wales they provide a useful proxy of what may happen in Scotland.
The following projected changes are therefore anticipated to take place in the future:
- The proportion of the rail network located in areas at risk of flooding is projected to increase
- Rail infrastructure that is 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
 Indicator BT2 provides a more detailed description of the assessment of climate projections and associated impacts on biophysical systems (the precursor of risks and impacts to socio-economic systems).
There are several key limitations to the assessment as summarised below:
- Major railways located in the floodplain are often raised above the ground surface on embankments. The difference in elevation afforded by these embankments is not always identified in flood modelling and mapping (Thornes et al, 2012). Therefore, flood risk to rail infrastructure may be over-estimated – i.e. where the embankment would raise the railway out of the inundated area and this is not reflected in the modelling due to the granularity of SEPA’s flood hazard modelling process.
- The consideration of what might happen in the future in terms of flooding-related climate risks to the rail network are based on English and Welsh data from the UK CCRA and so must be interpreted with caution for the Scottish rail network.
- Network Rail’s Network Links Layer which was used in this analysis includes double sections of track at many locations as well as railway siding etc. Thus that the total length of track used in this analysis does not correspond with the length of track published by Transport Scotland (2014) which counts one kilometre of single or double-track as one kilometre of route length.
- This assessment was only undertaken for 0.5% probability (1:200 year) modelled flood events. These are low probability events located at the more severe end of the flood event spectrum. Higher probability events (e.g. 1:10, 1:50) can be expected to affect a smaller extent of the network than 1:200 year events but on a more frequent basis. The he flood hazard modelling is based on historic data. As a result of climate change, the magnitude of a 1:200 year event may be greater than represented in this analysis.
- Given the nature of the modelled data used for these metrics it is not possible to compare either the likelihood or the potential consequences of flood events in relation to other types of disruptive event (such infrastructure problems or other extreme weather events).
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]
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]
SEPA (2015) Flood Risk Management Strategy Characterisation Data
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 (2014) Scottish Transport Statistics, No. 33, 2014 Edition. Available at http://www.transportscotland.gov.uk/statistics/j357783-00.htm [accessed 11/08/2015]
SEPA provided spatial data on rail network flood risk assessment from an early version of their Flood Risk Management Strategy Characterisation Data (SEPA, 2015)
Network Rail provided spatial data for the Scotland Route.
The analysis and development of this indicator was undertaken by Dr Neil Ferguson (University of Strathclyde) and Dr Peter Phillips (Collingwood Environmental Planning Limited).