Guidance Preparing for Climate Change

Preparing for climate change: climate risk-based decision-making in strategic transport planning and design

Transport in south east England is often adversely affected by extreme weather events including high and low temperatures, intense precipitation, high winds and storms – many of which are expected to worsen with climate change. These climate hazards can cause adverse effects to transport assets and users, from events such as surface water, fluvial, groundwater and coastal flooding; overheating; coastal erosion; landslips and subsidence; and wildfires. It is important that Local Transport Authorities (LTAs) account for these impacts when making strategic transport planning decisions, considering both present-day and future impacts accounting for climate change.

This guidance has been prepared to provide LTAs in the Transport for the South East (TfSE) region with guidance on preparing for ongoing and future climate change. The guidance will first present a summary of the key climate hazards and trends facing south east England – a first step to undertaking a climate change risk assessment. This will be followed by a summary of how climate change risk assessments can play an important role in the early stages of strategic transport planning and the decision-making process of new transport schemes, as well as inform their design.

The future climate hazards facing south east England

In the future, south east England is expected to see warmer and wetter winters, hotter and drier summers and more frequent and intense weather extremes. The UK Climate Projections from the Met Office highlight the following key trends in climate hazards out to 2080:

1. Increasing heavy precipitation events and likelihood of flooding.

• Winter rainfall is likely to increase by 20-30%. While overall summer rainfall is expected to decrease by 30-40%, heavy

rainfall events in summer are anticipated to become more frequent and extreme, causing ‘flash’ flooding.

2. Rising sea levels and increased storm surge heights, affecting coastal flooding and erosion.

• Sea level rise is projected to increase by up to ~0.8 metres.

3. Increases in extreme high temperatures and more frequent and/or prolonged heatwaves.

• Summers are likely to be hotter by around 5-6°C, while winters are likely to be warmer by around 3-4°C; cold events

will still occur but may be less frequent.

4. Increasing frequency and magnitude of storms.

Other climate hazards that can affect transport infrastructure include subsidence, high winds and slope and embankment failure, as outlined in the UK Climate Change Risk Assessment Transport briefing.

The policy context for addressing climate risk and adaptation in UK transport

In April 2024, the Department for Transport (DfT) published its draft Transport Climate Adaptation Strategy, with four key pillars with associated actions aimed at key actors including transport infrastructure operators (TIOs):

1. Culture: embedding climate risk across the transport sector

2. Economics: identifying the financial case for climate adaptation

3. Regulation: setting the long-term direction

4. Collaboration: working with others to address climate risks and build resilience

These four pillars form golden threads throughout this article, which discusses how climate risks can be addressed through strategic transport planning and design processes.

Early consideration of climate risks is key

Transport assets can have a long lifespan. According to the DfT’s Transport Climate Adaptation Strategy, new schemes such as HS2 are designed with a 120 year lifespan. Meanwhile, 85% of rail infrastructure assets in use today could still be in place by 2055. As such, it is vital they are designed to be resilient under future climates; a climate change risk assessment is the first step towards transport resilience.

Climate change risk assessments are a useful tool to identify climate-related impacts and assess their likelihood and consequence. As with all risks, the most effective way of managing climate risks is to design them out of a project, and so it is important to have consider climate impacts early on a transport scheme project, from optioneering through to detailed design, build, operation and maintenance. Identifying severe climate risks early on in project conception help to avoid expenditure on unviable projects.

The role of Environmental Impact Assessment in decision-making

While earlier identification of key climate risks is important to scope out unviable projects, an Environmental Impact Assessment (EIA) plays an important role in the reporting of climate risks and resilience on transport scheme projects. Useful guidance on delivering climate resilience and adaptation components of EIA for new projects has been developed by the Institute of Environmental Management and Assessment (IEMA). Collaboration with the EIA water team is vital to ensure alignment in understanding of flooding and drought related climate risks. Standardised frameworks, such as ISO 14091:2021 Adaptation to Climate Change – guidelines on vulnerability, impacts and risk assessment, help to guide a best practice approach to assessing risks and building resilience. Using this framework ensures a consistent methodology is applied, findings can be compared and opportunities for collaborative responses can be identified between stakeholder groups.

Empowering all involved in transport schemes to identify and address climate risks

The risks of not adequately accounting for climate change can be catastrophic, with risks often sitting across all aspects of project design. Examples include drainage systems that are insufficiently sized to handle future extreme rainfall volumes, and bridge expansion joints for which future extreme high temperatures may exceed design standards. The process of developing climate change risk assessments therefore needs to be well-integrated with design teams. It is important that all contributors to the strategic planning and design process are empowered to raise climate risks concerns, with climate risk professionals appropriately represented in all stages of design. Upskilling all contributors can be a good way of achieving this, such that they can help identify and raise potentially adverse climate impacts and be empowered to challenge the ‘status quo’ or business as usual approach to design. Transport for London (TfL) is one organisation delivering this upskilling via internal training on climate risk and adaptation, in response to an action set out in the TfL Climate Change Adaptation Plan.

Designing for a changed climate

The design stage of a transport scheme is often underpinned by engineering and technical standards. However, while many of these have weather-related aspects – many have not been updated to consider climate impacts. It is important these are identified and suitably handled collaboratively between the engineering and climate teams. This could include identifying more resilient materials to use in construction, stress-testing levels of service under different climate scenarios or adding mitigation measures to manage residual climate risk. It is important to test any implemented mitigation measures to ensure they adequately manage the identified climate risks – this could be via modelling, or ongoing monitoring.

A significant challenge of designing for a future climate is the degree of uncertainty – it is not clear the degree to which global greenhouse gas emissions will be mitigated, and climate projections themselves include a degree of uncertainty. A way of handling this uncertainty when designing new transport schemes is to take an ‘adaptation pathways’, future-proofing approach to design. For example, drainage systems can be designed flexibly such that their capacities are able to be easily changed or upgraded at the end of assets’ design life.

Seek agreement on risk tolerance

For various reasons, it is not feasible to remove all possible risks from transport projects. For example, many popular cycling greenways are located along rivers, creating amenity benefits. However, this puts the greenways at risk of flooding when river flows are high. Designing out the risk of flooding to greenways by raising their elevation or adding flood defences can be prohibitively expensive, in terms of cost and carbon, and can also disrupt the landscape. Therefore, it is important that LTAs agree the level of tolerated risk on transport projects. Communicating this with end users is also important to avoid adverse operational impacts.

After design – effective maintenance and operation is key to building climate resilience

Once transport schemes are designed, constructed and in use, it is vital that they are maintained as per design expectations. For example, drainage systems must be cleansed and maintained to enable them to work at their design capacities. Without this maintenance, the risk of flooding can be much higher than as agreed and set out in project’s design standard.

In addition to the physical measures taken to minimise climate risks at the design stage, building operational resilience to extreme weather events helps to manage the residual climate risks. Severe weather plans, which set out steps to manage before, during and after extreme weather events, are a good way to build this resilience.

Continue the collaboration

When planning for and designing transport schemes, it is important to collaborate with climate risk management authorities such as the Environment Agency, water companies, National Highways and neighbouring local authorities. It is important to note that non-flood related climate risks do not currently have clear risk owners.

As outlined in their Transport Climate Adaptation Strategy, the DfT is also working to give infrastructure operators the tools and evidence they need, supporting a consistent approach to identifying climate risks and adaptation measures. It is recommended that LTAs engage with this process to ensure the tools are applicable at the local scale, as well as for national transport organisations.

The interconnected nature of transport infrastructure means that impacts on one network can cause cascading impacts on others. For example, if a rail line is rendered inoperable, passengers may transfer to road infrastructure, presenting traffic management challenges. Therefore, a joined-up approach to adaptation at a whole system level - as well as for individual assets or networks - should be considered.

For further information on a lived experience example on this topic. Please read our case study on PLA Zero Emission Crossings – A Thames River Crossing Study. by clicking here

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