Climate Change Provisions for CSA S6:25 Canadian Highway Bridge Design Code: Findings and Recommendations


Executive Summary

The purpose of this project was to research and develop recommendations and guidance on the potential impacts of climate change for integration into the 2025 editions of CSA S6, Canadian highway bridge design code (CHBDC) and CSA S6.1, Commentary on CSA S6.

Through the development of new bridge design requirements in this area, CSA Group will help advance the National Research Council of Canada (NRC) mandate to provide Canadians with the essential knowledge, direction, and tools necessary to actively strengthen the climate change resiliency of Canada’s infrastructure.

Climate models project that greenhouse gas emissions will increase both global temperatures and the frequency and intensity of extreme weather events throughout many parts of the world. As a northern country, climate change is amplified in Canada compared to other countries. Since 1950, the annual average surface air temperature over Canada’s landmass has warmed by 1.7°C, approximately twice the global average. Total annual precipitation across Canada has increased and it is likely that the frequency and severity of extreme weather events, such as heat waves, droughts, extreme winds, extreme precipitation, and floods will also change.

Canada’s infrastructure, which includes buildings, bridges, roads, transit, power, water, and wastewater systems, could be at risk if actions are not taken to address expected changes in climate conditions and extremes. Climate change is expected to affect the magnitude and frequency of different weather parameters, such as rainfall, wind, and snow, and their associated climatic loads. This could lead to reduced safety, serviceability, and service life of this infrastructure. The consequences of failure could be significant and may include fatalities, injuries, and illnesses, loss of function and service disruption, high rehabilitation and replacement costs, and significant negative socio-economic impacts.

Highway bridges are critical links in the Canadian transportation network and key components of Canada’s core public infrastructure. The design of highway bridges is currently based on historical climatic data that assume climate stationarity. Such assumptions are no longer valid as historical climatic data is no longer a reliable predictor of future climatic conditions and associated loads. Due to changing climate and climate nonstationarity, highway bridges could be vulnerable to a range of climate hazards, which could result in increases in the intensity and frequency of extreme load effects from extreme temperature, precipitation, and wind that, in turn, could reduce their safety, serviceability, post-event function, or durability. To minimize the risk of failure of bridges due to climate change and extreme weather events, new provisions must be developed for the design of highway bridges that enhances their resilience. The consideration of climate change in the design of highway bridges will lead to improved life cycle performance and minimize the risk of failure and the need for costly maintenance, repair, and rehabilitation. The development and implementation of new climate change provisions for the 2025 edition of the CHBDC will lead to more climate-resilient bridges and provide for a more uniform and lower risk of adverse consequences across Canada.

Project Approach

This project entailed a series of key research activities in combination with stakeholder and CSA CHBDC member engagement to identify and study the major risks to bridge infrastructure related to climate change, and to develop recommendations and guidance to reduce the identified risks. The resulting climate change adaptation recommendations have been submitted to CSA’s CHBDC Technical Committee and Technical Subcommittees for inclusion in the 2025 Code and Commentary. See Appendix A for a summary of the structure of the CSA S6 committees and subcommittees, as well as a description of the various sections of the CHBDC.

The following tasks and methodology were carried out during this project:

Stakeholder Consultations

Subject matter experts were engaged to evaluate how CHBDC users perceive and experience climate change-related impacts and current climate change adaptation practices. Selected stakeholders participated in an initial interview. Subsequently, three one-day stakeholder workshops were held in Montreal, Toronto, and Vancouver to further discuss risks and necessary adaptation measures, identify existing industry best practices, and to seek input on climate-related issues that codes and standards are not currently addressing and suggestions on the types of climate change adaptation solutions that should be considered. Summary reports from the stakeholder interviews and workshops provided key input for the subsequent tasks.

General Recommendations for CSA S6:25 and S6.1:25

General recommendations for climate change adaptation of highway bridges that could be included in CSA S6:25 and CSA S6.1:25 were developed and included the following considerations:

  • Potential impacts of climate change on the intensity and frequency of climatic loads on bridge structures;
  • Potential impacts of climate change and extreme weather events on the safety, serviceability and durability of bridges;
  • Possible climate change adaptation measures to reduce the risk of failure of bridge structures; and
  • Ways to effectively integrate and stage climate-enhancing works into highway and bridge renewal plans within existing federal, provincial, territorial, and municipal frameworks.

This task also included the following actions:

  • Reviewing the 2019 CSA S6 provisions dealing with climate change and northern issues;
  • Assessing the new Environment and Climate Change Canada (ECCC) data, including environmental historical data up to and including 2017 and ice accretion maps, and the implications of the data for bridge design and rehabilitation; and
  • Reviewing the Public Infrastructure Engineering Vulnerability Committee (PIEVC) assessments on highway bridges that also deal with climate change and northern issues.

Development of Uniform Risk Approach

This task examined the impact of the regional varying statistics of climatic load factors on the reliability of designed bridges and identified the physical reasons for such variations. Current design for extreme climatic hazards in the CHBDC is based on the concept of “uniform hazard” or an event with geographically uniform probability of exceedance. Climate change is affecting various regions of Canada differently so it is necessary to investigate the impact of climate change (focusing on wind and precipitation) on the reliability of structures in different regions of Canada. There may be instances where the ratio of ultimate load design values to service load design values varies from region to region. To achieve acceptable and uniform levels of risk and reliability throughout the country for loading combinations where climatic loads dominate, new formats for the presentation of the design values of climatic loads, such as wind pressure and ice accretion were explored.

Climate Nonstationarity and Extremes

This task quantified the level of nonstationarity in expected climate conditions through an analysis of recent directly observed climate changes and projections of future change from climate model simulations.

In CSA S6:19, the concept of return periods for climatic loads has been a standard and important tool for bridge design. This is based on the assumption of a stationary climate, with the range of climate variability estimated from historical environmental information. However, an assumption of climate stationarity is not valid in the case of changing climate, leading to trends over time in mean climate conditions and trends over time in the frequency of reoccurrence of extreme climate events. Both effects ultimately lead to non-stationary climatic loads.

Climate conditions that were examined for recent observed and future projected changes are of direct relevance to bridge-relevant climatic loads and associated design life levels. Climate vulnerabilities will vary fundamentally by large-scale geography (e.g., permafrost degradation at high latitudes versus summer heat at low latitudes) and also by small-scale geography (e.g., snow loads at high altitudes and flooding in valley bottoms). To capture this heterogeneity, climate analysis was carried out on a nationwide high-resolution grid to assess the full range of site-specific bridge design vulnerabilities in a unified analysis framework.

This approach was needed to develop methods that integrate knowledge of non-stationary climate in design life levels of climatic loads and associated reliability targets to be met during the design life of the structures. Uncertainty in bridge design (type, location) and site-specific uncertainty in future climate projections were assessed to ensure the outcome accurately reflects the range of potential future design-side and climate-side risks.

Consideration of Localized Extreme Weather Events

This task assessed the need to update the representation of localized extreme weather events in CSA S6:19 to reflect current observational data. The current approach of the CHBDC is to specify loads at specific return periods and then apply time-invariant load factors to convert the loads to ultimate values for bridges. The design for some effects, however, are not “load” based, and require best estimates of weather events to assess bridge geometry, channel clearance, or scour protection. Some extreme weather events are not well represented in historical climatic and environmental data in CSA S6:19 and may also be poorly represented in current meteorological observations.

Climate Change Adaptation Implications on Bridge Design and Materials for Canada’s North

Canada’s North is experiencing the most accelerated change in climate in the country, with a 3.5°C increase in average temperature since the beginning of the 20th century. This, in combination with remoteness, inaccessibility, and aging infrastructure, means that the quality of life in northern communities has been impacted by climate change more than in other parts of the country to date. This task focused on developing the means for bridge designers to specify the composition, properties, and performance of the materials selected for the structure by taking into account the design loads and the expected environmental degradation during the service life of the structure or its elements.

Recommendations for the Implementation of Climate Change Provisions in CSA S6:25 and CSA S6.1:25

The deliverables of the previous six tasks informed the review, assessment, and formulation of recommendations to update existing and introduce new climate change adaptation provisions in CSA S6:25 and CSA S6.1:25, which will be proposed to CSA’s CHBDC Technical Committee.