Input data
The inputs below are what is required to identify the probability of weather-related transport threshold exceedance.
There are three, and they answer three different questions: which weather to investigate, at what value it bites, and what the weather is expected to do.
1. Source of climate risks of concern to transport systems
The first input is knowing which weather requires investigation in the first place.
Weather-related risks to transport have been determined through Climate Change Risk Assessments (CCRAs). Organisations across the surface transport sector, working in collaboration with Defra, developed a consistent approach to climate change risk assessment, aligned with international standards for climate adaptation and risk assessment (ISO, 2019; ISO, 2021).
As part of the CCRA process, organisations applied their sector-specific expertise to:
- Identify receptors within their systems that are exposed to climate-related hazards
- Assess the associated risks
Why start from the CCRAs
The operators already hold the domain knowledge about which parts of their systems are vulnerable and to what. Beginning from their assessments means the threshold work inherits that expertise, and because the CCRA approach is consistent across the sector and aligned to ISO standards, road and rail risks can be compared on the same terms.
2. Threshold values
Thresholds can take the form of a design standard, an operational limit or an observed point of failure, as set out in the overview. Each comes from a different kind of source.
Industry standards
Industry standards are a useful source of weather-related thresholds because they define the current design, construction and operational parameters of transport infrastructure.
The UK industry standards for road and rail are:
| Mode | Standard |
|---|---|
| Road | Design Manual for Roads and Bridges (DMRB) |
| Road | Manual of Contract Documents for Highway Works (MCHW) |
| Rail | Rail Safety and Standards Board (RSSB) |
| Rail | Catalogue of Network Rail Standards |
Policy documents
In addition to standards, industry produce reports specific to certain topics. There has been a rise in reports related to climate change, and some offer a valuable source for identifying thresholds.
| Document | What it offers |
|---|---|
| Fourth Round Adaptation Reporting Power (ARP4) reports from NH and NR | Outline the actions of each organisation to build resilience to climate change, and can provide a source for thresholds |
| National Highways, Climate Change and the Strategic Road Network: Building resilience for a changing future | A further example of a policy document carrying threshold information |
Published research
There are often several variables at play when considering weather-related risks to transport. Where this is the case, published research addressing a specific problem may be the correct source.
The Transport Research Laboratory (TRL), for example, has produced reports that address some of these.
Research often gives a formula, not a number
Published research frequently does not provide a single threshold value. What it provides instead is often a simple formula that can be applied to devise a threshold from localised values and historical data.
This is the source of the formula-based thresholds described in threshold identification.
3. Future climate projections
The third input is what the climate is expected to do.
| Source | UK Climate Projections 2018 (UKCP18), or other relevant climate projection datasets where appropriate |
| Provides | Future projections of climate variables corresponding to the identified transport-specific thresholds, such as precipitation intensity, temperature, wind speed and other relevant hazard indicators |
These projections provide the future environmental conditions against which threshold exceedance can be assessed.
See climate scenarios for how UKCP18 is used elsewhere in the IMP.
Putting the three together
The three inputs combine into a spatial comparison.
By spatially overlaying or comparing projected climate conditions with transport-specific threshold values, locations where thresholds are more frequently or more severely exceeded can be identified.
That comparison enables the identification of potentially vulnerable transport assets and areas under future climate scenarios, supporting:
- Spatial risk assessment
- Resilience planning
- Prioritisation of adaptation measures
Frequency and severity, not just yes or no
The comparison asks how often a threshold is exceeded and how severely, not merely whether it is crossed at all.
That distinction is what turns the output into a prioritisation tool. An asset whose threshold is exceeded twice a decade and one exceeded twenty times a year are both "at risk", but they are not the same investment case.