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Delivering a climate change resilient railway

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Resilience is core to being a good business. One of the greatest risks that businesses face is adapting to climate change. HS2 is mitigating climate change by reducing its emissions, including implementing and delivering tough carbon reduction targets. However, even given efforts to limit the cause of global warming, further climatic changes are inevitable in the future and HS2 will need to manage the growing risks from climate change, including warmer, wetter winters and hotter, drier summers, as well as more extreme weather.

This paper sets out the challenge faced by HS2 Ltd, how HS2 is being designed and built to be climate-resilient in the long term as well as information on bespoke and innovative processes, which have fed into industry best practice and guidance and climate-resilient design solutions. Climate change adaptation and resilience risks will continue to be managed throughout the design, construction, operation and maintenance of HS2. However, the end goal is clear – creating a high-speed network which is climate-resilient for the long term.


Climate change resilience and adaptation planning take time, especially for infrastructure, which means assessment work needs to start early in planning any new infrastructure to avoid being ‘locked-in’ to potentially high levels of risk.

Adapting to new climatic conditions is a relatively new scientific area. HS2 Ltd has led the way for large infrastructure projects by assessing how climate change will affect resilience throughout the project, including in its environmental statements, standards and requirements for its contractors to ensure climate change adaptation and resilience is baked-in to design and construction.

The challenge

Existing railway infrastructure in the UK and elsewhere is significantly impacted by extreme weather conditions, causing delays and potential safety issues, with associated costs. This can lead to loss of confidence in the service and potentially willingness to use the service. For example, heavy rainfall can lead to flooding (see Figure 1)[1], stopping trains from running and damaging railway infrastructure, sometimes causing months of costly repairs. Flooding can lead to landslips, which tend to affect large areas and need substantial engineering work to make the railway safe again. These impacts cause delays to journeys and have a significant impact on performance of railway infrastructure.

A picture of  flooding on some railway tracks
Figure 1. Railway flooding[1]

The Climate Change Committee[2] states that “We know with high confidence that climate change is happening today and is the result of greenhouse gas emissions caused by human activity”. Impacts from climate change are already being felt today and will continue to increase in the future. Action to limit future global greenhouse gas emissions will help restrict future changes in the climate system. To avoid the worst effects of climate change, Paris Agreement targets a global temperature rise threshold of well below 2°C, ideally 1.5°C. The UK has responded with a world-leading target of net zero greenhouse gas emissions by 2050. However, the Climate Change Committee state that “current global plans give only a 50% chance of meeting 3 degrees celcius”.

Even if the world now cuts greenhouse-gas emissions dramatically, the climate change effects will continue. Large bodies of water and ice can take hundreds of years to respond to changes in temperature and it takes decades for CO2 to be removed from the atmosphere. As the world warms, this leads to more extreme weather, such as heavy rain, causing flooding and heatwaves causing drought. Unmitigated, this extreme weather will have severe impacts on infrastructure.

HS2 policy response

HS2 Ltd has responded to the challenge of climate change with a policy “to build a high-speed network which is climate-resilient for the long term, minimises our carbon footprint and delivers low carbon, long distance journeys, that are supported by low carbon energy”. HS2 Ltd is mitigating climate change by reducing its emissions, including implementing and delivering challenging carbon reduction targets. For example, the carbon footprint of HS2 construction will be reduced through the challenging carbon reduction targets. HS2 will deliver those targets by encouraging innovation and best practice. Reducing carbon can also reduce costs through, for example, energy efficiency and reducing materials in construction. This brings benefits both to HS2 and the wider supply chain as well as other projects that can learn from our experience.

Even given efforts to limit the causes of global warming, further climatic changes are inevitable in the future and HS2 is acting now to manage the growing risks from climate change, including warmer, wetter winters and hotter, drier summers and more extreme weather. HS2 is one of the first projects to assess climate change resilience in all key stages of the project, including the Environmental Impact Assessments through to the design and construction of the project.

Climate projections

Climate change will cause existing weather patterns to shift, changing the severity, frequency and impact of events. Ensuring HS2’s resilience could become increasingly challenging without integrating the likely future climate into HS2 designs and construction as well as future maintenance and operating procedures. The climatic changes could amplify the risk and impact of asset failures, possibly to unacceptable levels for future operations. Such shifts will mean that historic records of likelihood, severity and impact cannot be relied upon to inform the future. HS2’s approach is to consider these changes in risk assessments and plan accordingly that we can plan to cope with the likely future climate.

These climate changes can be understood in more detail by utilising the Met Office climate projections, UK Climate Change Projections 2009 (UKCP09) and UKCP18. UKCP09 was recently superseded by UKCP18. UKCP09, which used the Special Report on Emission Scenarios (SRES) scenarios, did not include any policies to limit climate change and therefore did not consider climate change mitigation. The increasing relevance of mitigation scenarios led the climate research community to develop a new set of scenarios, or pathways called Representative Concentration Pathways (RCPs) which are the basis for the most recent UKCP18 climate change projections.

For example, Figure 2 shows that in all scenarios, temperatures will continue to rise until at least the 2050’s.

Chart showing global mean temperature projections.
Figure 2. Global mean temperature projections.

Figure 2 is from a climate model (called MAGICC6) relative to a pre-industrial average (1850-1900) for RCP2.6 (blue), RCP4.5 (green), RCP6.0 (yellow) and RCP8.5 (red) and the older SRES scenarios (dashed coloured lines). The RCPs can be represented by the levels of temperature change that result from each scenario. RCP2.6 (blue in Figure 2) represents a pathway where greenhouse gas emissions are strongly reduced, resulting in a best estimate global average temperature rise of 1.6°C by 2100 compared to the preindustrial period. RCP8.5 (red in Figure 2) is a pathway where greenhouse gas emissions continue to grow unmitigated, leading to a best estimate global average temperature rise of 4.3°C by 2100. RCP4.5 and RCP6.0 are two medium stabilisation pathways, with varying levels of mitigation[3].

HS2 has so far based climate change assessments on UKCP09. However, the projections have now been replaced by UK Climate Projections 2018 and HS2 is in the process of updating design guidance accordingly.

Climate change in HS2 Environmental Impact Assessments

During the Parliamentary Design stage, Environmental Impact Assessments (EIA) for Phase One and 2a (and Phase 2b EIA when completed) assessed climate change adaptation and resilience in two ways:

  • A high level climate change resilience assessment, which uses climate change risk assessment techniques to assess the resilience of the proposed infrastructure. Multi-disciplinary teams across the business working with leading environmental consultancies have undertaken climate change resilience assessments to identify the potential risks of climate change and to assess HS2’s resilience and capacity to cope with these potential risks. The assessments considered risks posed by climate related hazards such as extreme hot and cold weather, heavy rain, high winds and storms to the infrastructure and assets associated with the railway including tracks, tunnels, overhead line equipment, rolling stock, stations and earthworks. The likelihood and consequences of climate hazards were considered based upon the trends within the UK climate projections.  
  • A climate change in-combination climate change impact assessment, which includes consideration of the combined impacts of HS2 and potential climate change on the receiving environment (e.g. ecology, landscape, historic environment) and community, based on trends within the UK climate projections. Although not the subject of this paper, it is an important part of the work to understand the impact of climate change on the surrounding environment of HS2.

The methodology and results of these assessments have been included in the Phase One and Phase 2a Environmental Statements[4][5] and also being undertaken for the emerging Phase 2b environmental statement. More information can be found in HS2’s information papers/environmental statements online [6][7].

The assessment methodology was developed for HS2 and has been cited in guidance from the Institute of Environmental Assessment and Management, Environmental Impact Assessment Guide: Climate Change Adaptation and Resilience [8].

The Adaptation Sub-Committee report, Managing Climate Risks to Well-Being and the Economy[8] report stated “The comprehensive approach taken by the HS2 Environmental Statement to the full range of climate risks serves as an example of good practice”

HS2 climate change requirements for design and construction

HS2 has key requirements, standards and supporting climate change assessments which engineers/designers/contractors use to assess and integrate climate change adaptation and resilience. These include:

  • The bespoke HS2 Climate Change Adaptation and Resilience Technical Standard provides the HS2’s requirements and associated guidance for managing climate change resilience associated with the design, construction and operation of HS2. It supports the commitments made in HS2 Ltd’s Sustainability Policy and Environmental Policy. The climate change resilience requirements set out in the technical standard apply to all design, construction and operation activities associated with the delivery of HS2 except where the technical requirements of other stakeholders take precedence (e.g. HS2 trains running on non-HS2 network). They apply to all HS2 Project stages.
  • The Climate Change Design Impact Assessment (CCDIA), for assessing the resilience of standards and/or designs to future climate change, in order to inform their development. The CCDIA defined the relevant HS2 assets and their expected design lives, then used the UKCP09 projections to assess the potential impacts on the design and performance of the system and/or asset. The outcomes of the CCDIA provide the evidence to support design decisions that are proportionate to the impacts and risks identified or identify if further work is required. Where possible, adaptation of the design parameters or mitigating approaches as identified by the CCDIA have been incorporated into the technical standards for each relevant asset / topic area.
  • Climate Change Resilience and Interdependencies Assessment (CCRIA) A modern, efficient, networked infrastructure necessarily creates interdependencies between different infrastructure sectors. Local and national infrastructure also interconnect, especially in the transport sector. The key HS2 interdependencies that are affected by climate change have been identified, as well as a method for categorising, assessing and prioritising vulnerabilities relating to the effects of climate change at an asset group level. These interdependencies include the classic rail network, road infrastructure, power infrastructure, and telecommunications networks. The technical standard sets out the requirements for reviewing the CCRIA, to be carried out by the contractor in collaboration with HS2, as the design progresses.
  • The High Speed Rail (London-West Midlands) – Environmental Minimum Requirements – Annex 1: Code of Construction Practice (CoCP)[9] sets out a series of principles to be applied to HS2 and its contractors throughout the construction period of Phase One (separate CoCPs for further phases will be developed). Consideration of extreme weather events in the construction period is covered here. including to use a weather forecasting service from the Met Office or other approved meteorological data and weather forecast provider to inform short to medium-term programme management, environmental control and impact mitigation measures. In addition, there is a requirement to register with the Environment Agency’s Floodline Warnings Direct service in areas of flood risk.
  • Technical standards or other documents have an important role to play in supporting climate change resilience. A number of requirements for climate change adaptation in the design stage are integrated into other standards (such as a climate change allowance for an environmental parameter on top of an existing level of design). A range of measures are now embedded within the design of HS2, for example: HS2 infrastructure is designed to be resilient to 1 in 1000 year flood events.
  • HS2 also requires (for example for Stations), that BREEAM credits for climate change adaptation. Complying with this technical standard, and the climate change adaptive measures in other technical standards, constitutes progress towards BREEAM Infrastructure requirements for resilience (reducing risks resulting from natural hazards exacerbated by climate change) and stakeholders (resilience to future needs and interdependencies across the entire operational lifespan).

Climate change resilience considerations in design and construction

Resilience can be described as the capacity, or ability, of a system to absorb stresses caused by climate change and retain its function. It has four aspects:

  • Resistance, which concerns physical protection;
  • Reliability, which is the capability of the infrastructure / asset to maintain operations under a range of conditions;
  • Redundancy, which is the adaptability of the infrastructure system / network (for example, individual assets can have redundancy, e.g. additional space for increased ventilation), and;
  • Response and recovery, which is the ability to recover from a disruption to return to functionality.

Most of the requirements in HS2’s Climate Change Adaptation and Resilience Technical Standard, and those in other HS2 civil engineering technical standards relating to climate change, are concerned with ensuring the resistance of assets is such that their reliability remains satisfactory throughout their design life. However, considering reliability, redundancy and response and recovery in the design of infrastructure is also beneficial, as decisions taken now can have a bearing on the cost of responding to disruptions later in asset design lives.

Resilience is linked to climate change adaptation, which can be considered the actual adjustment or design intervention that prevents or minimises the impact, or exploits a beneficial opportunity, of projected or actual changes in climate. When the designed lifespan of an asset is the entire lifespan of the HS2 infrastructure (such as earthworks), decisions made in the design stage regarding the level of resistance of an asset are of paramount importance as there are limited opportunities to adapt in the future (particularly without significant impact on performance) .

The work that HS2 is undertaking ensures that HS2 is designed with climate change resilience built-in, therefore reducing the impact of climate change throughout the design lifespan of HS2.

Adaptive management is the process that enables uncertainty to be included in operational decision-making. For HS2, this means foreseeing potential climate change risks and ensuring HS2 Ltd assets are able to adapt during the operational phase, even if it is not viable to embed the climate change adaptation during the initial build design (i.e. increase the resistance of the design beyond what is practicable given the uncertainty involved).

HS2 asks its contractors to consider what adaptive management may be required so that designs for HS2 infrastructure should not preclude opportunities to adapt in the future.

Examples of this could include building ventilation shafts in a manner that allow for changes to ventilation standards as climatic thresholds / triggers are crossed, or employing different flood risk measures once a certain risk of overtopping / lack of functionality is projected within the asset design life. Increasing the magnitude of the environmental hazards to which assets can maintain functionality in the initial design only builds the resistance of the assets. Fully resilient assets, or group of assets, are also able to further adapt to change during the design life. This is important to HS2 given the long design life of the project itself, the uncertainty involved with projecting greenhouse gas emissions and the impacts of climate change, and the highly variable design lives of individual assets.

Table 1 provides some examples of proposed design solutions to climate change risks identified by HS2 contractors.

Asset TypeHazardExamples of Proposed Design Solutions



Inclusion of wind barriers


Increased structural rigidity


Aerodynamic bridge deck design


Soil moisture deficit

Replacement of clays with other materials



Stabilisation and addition of moisture reducing agent to limit potential shrinkage


Design and management of lineside vegetation to reduce soil moisture deficit



High level of water efficiency and rainwater recycling to reduce demand for potable water


High Temperatures

Shading options, including trees and active shading devices

Passive building design – exposed mass within floor surfaces and walls can be used to absorb incidental solar gain entering through the roof-lights and other unshaded glazed areas to reduce resultant rises in indoor air temperature

Stations/Vent Shafts

Peak rainfall and flooding

Blue roof and green roof designs

Increased vegetation in the public realm

Table 1 Examples of Design Solutions


One of the most exciting and important areas of climate change work is collaborating. It is a fundamentally important part of working in climate change as the reach of the work means that it is not a job that any one person is able to undertake and it needs to be delivered throughout the organisation. An example within HS2, is the Climate Change Adaptation Forum, including, engineers, architects, and environmental leads.

Externally HS2 collaborates with industry partners and other organisations to share and push forward knowledge of climate change adaptation and resilience. These include Network Rail, the Railway Safety and Standards Board (RSSB), the Infrastructure Operators Adaptation Forum, Natural Environment Research Council Environmental Risks to Infrastructure Programme (NERC ERIIP) and working with government departments such as Department for Transport (DfT) and the Department for Environment, Food and Rural Affairs (Defra).

HS2 has also worked, as part of the BSI Greenhouse Gas Committee, on the first standard on climate adaptation, BS EN ISO 14090 Adaptation to climate change – Principles, requirements and guidelines. It offers a framework that enables organisations consider climate change adaptation when designing and implementing policies, strategies, plans and activities. BS EN ISO 14090 is the first in a range of ISO standards in this area and aims to help organisations assess climate change impacts and put plans in place for effective adaptation. The standard sets out how organisations can prioritise and develop effective, efficient, specific and deliverable adaptations which will increase resilience and demonstrate robust and credible risk management, amidst the impact of climate change.


HS2 is preparing to adapt to climate change, considering and addressing climate change impacts from the earliest stages of environmental impact assessment, through design and construction and into operation and maintenance. This paper has provided an insight into the many workstreams, assessments, standards and requirements as well as other considerations about climate change adaptation and resilience that are in play. This work requires understanding and assessment of climate change risks as well as collaboration across HS2 and externally to continue to implement and increase knowledge in this relatively new area. Climate change adaptation and resilience risks will continue to be addressed throughout the design, construction, operation and maintenance of HS2. However, the end goal is clear – creating a high-speed network which is climate-resilient for the long term.


[1] Climate Change Adaptation Report, Network Rail (2015), Accessed 9 November 2020

[2] Climate Change Committee, Accessed 17 February 2021

[3] UKCP18 Guidance: Representative Concentration Pathways, Met Office (2018), Accessed 9 November 2020

[4] HS2 Phase One environmental statement: documents (2013)

[5] HS2 Phase 2a environmental statement (2019)

[6] High Speed Two Phase One Information Paper, E9: Climate Change Adaptation and Resilience, HS2 (February 2017), Accessed 9 November 2020

[7]High Speed Two Phase 2a Information Paper E26: Climate Change Adaptation and Resilience, HS2 (July 2017), Accessed 9 November 2020

[8] IEMA EIA Guide to: Climate Change Resilience and Adaptation, IEMA (2020), Accessed 9 November 2020

[9] Managing climate risks to well-being and the economy, Adaptation Sub-Committee (2014), Accessed 9 November 2020

[10] Environmental Minimum Requirements Annex 1: Code of Construction, High Speed Rail (February 2017), Accessed 9 November 2020