City of Calgary's Stephen Avenue Climate Resilience Assessment

In 2022, the City of Calgary worked with Stantec Consulting Ltd. (Stantec) to conduct a Climate Risk and Resilience Assessment (CRRA) for the planned redevelopment of Stephen Avenue (The Project). Stephen Avenue is considered an iconic and historic street in the heart of Calgary. It serves as a cultural hub, a tourist attraction, a business district, and a vibrant place for everyday life. Despite these strengths, Stephen Avenue has reached the end of its usable lifespan and needs a refresh to ensure its success in the future. Furthermore, changes in the magnitude and frequency of climate change-related events prompted The City of Calgary to conduct a CRRA for the planned re-development of Stephen Avenue to better prepare for a changing climate.

The CRRA showed that the biggest risks to Stephen Avenue are related to an increased frequency and severity of extreme heat events and severe storms. The assets likely to be at the greatest risk in the future include street trees, humans, gardens/flower beds and asphalt if no adaptation responses are incorporated into the design.

As part of the assessment, City staff and the design team proposed 30 adaptation measures to help reduce the potential impacts of climate change on infrastructure. For example, planting more trees with larger canopies and other vegetation to increase shade, establishing an emergency budget for rapid response to events, implementing permeable paving and underground drainage and reducing asphalt and hardscape areas for heavy rainfall events. Incorporating the recommended adaptation measures into the design phase of The Project supports the City’s vision for Stephen Avenue as a forward-looking, 21st-century street that continues to foster vibrant public life in the heart of Calgary.

Understanding and Assessing Impacts

To better understand how Calgary’s climate may change in the future, The City partnered with the Calgary Airport Authority, Pacific Climate Impacts Consortium (PCIC) climate experts, and GHD (an engineering consultancy with climate experts) to develop climate projections that could be used for risk assessments as well as adaptation planning and other engineering projects. Details on the climate projections are summarized in the Climate Projections for Calgary Report, available online.

Historical weather data was sourced from the Environment and Climate Change Canada (ECCC) station at the Calgary International Airport (which began monitoring in 1953), with quality assurance/quality control conducted by The City of Calgary from 1960-2014. Observed precipitation, air temperature, wind speed and direction, relative humidity, and solar radiation data was collected from the airport. The historical data was then perturbed to the climates of the 2050s and 2080s. The climate projections utilized the Canadian climate normals period (1981- 2010) as the Global Climate Model (GCM) baseline period. The 2050s climate was based on the GCM projections for 2041 to 2070 (mid-century), and the 2080s climate was based on the GCM projections for 2071 to 2100 (end-of-century). Additionally, the climate projections utilized the ensemble of the CMIP5 global climate models for the RCP8.5 emissions scenario.

PCIC downscaled the daily air temperature and precipitation data using a statistical downscaling methodology (e.g., the Bias Corrected Constructed Analog with Quantile mapping, version 2 [BCCAQv2]) to a grid of approximately 6 by 10 km. The PCIC data include 27 GCMs, and three GCMs have two runs each, for a total of 30 data sets at this grid size. The grid size was selected based on the availability of gridded historical climate observations. The wind, solar radiation, and relative humidity data were dynamically downscaled with Regional Climate Models (RCMs) to a grid approximately 15 by 25 km through the North America Coordinate Regional Downscaling Experiment (NA-CORDEX). The grid size was selected based on the availability and resolution of RCMs. Data for up to 16 GCM pairs is available through this data source. The available high-resolution datasets are currently the highest-resolution data available and provide a clear climate change signal for Calgary within the level of certainty available in current climate modelling.

For the Stephen Avenue CRRA, The City of Calgary utilized The City’s climate projections to determine climate likelihood scores, in combination with assessing historical weather impacts to determine consequence scores to assess climate risk to The Project. The climate hazards of interest that could affect The Project include: extreme heat, increasing air temperatures, wildfires, drought, short-duration high intensity rainfall, severe storms, high winds, heavy snowfall and river flooding.

Based on The City’s climate projections, more frequent and extreme heat events and severe storms are expected. For example, on a 5-point likelihood scale, severe storms are projected to increase from a 3 (possible) in the baseline time period to 4 (likely) in the 2050s and 5 (almost certain) in the 2080s. Combining likelihood with consequence and exposure puts humans and built infrastructure along Stephen Avenue (e.g., street furnishings, electrical transformer boxes and hardscape) at high risk from severe storms (hail, lightning, wind, intense rainfall). Additionally, as Stephen Avenue currently lacks shading in many areas, extreme heat could significantly put the most vulnerable users at risk and those dependent on walking or transit.

To support the climate data, three workshops were held with City staff to explore: possible impacts and past climate-related events; the consequence scoring for the identified impacts and; the feasibility of risk treatment measures. Workshop participants felt street trees and humans were the most vulnerable to climate hazards and intense short-duration rainfall and river flooding were hazards that could impact the most assets on Stephen Avenue.

Identifying Actions

Increased trends in the magnitude and frequency of climate hazards prompted The City of Calgary to develop a Public Infrastructure Climate Risk Assessment process that aligns with the Public Infrastructure Engineering Vulnerability Committee (PIEVC) Protocol and Infrastructure Canada Climate Lens requirements. The City’s Risk Assessment process includes specific criteria that outline when a CRRA must be undertaken by The City, accounting for factors such as the infrastructure’s lifespan, value, and ability to reduce climate risk. These criteria, along with the City’s Sustainable Building Policy and federal funding applications (e.g., Disaster Mitigation and Adaptation Funding funding), served as drivers to undertake CRRAs. A CRRA aims to identify a series of recommendations that could be integrated into the design stages of a new infrastructure or retrofit project to reduce climate risks to infrastructure and users.

Using The City’s CRRA process, climate data and pre-determined (already calculated and provided by The City) likelihood scores, Stantec engaged with City staff and members of the design team in three virtual workshops to complete the following:

  1. Impacts assessment (1st workshop) – Workshop participants evaluated how past and projected climate hazards have and may impact assets, operations, maintenance and users along Stephen Avenue based on previous experiences and potential future impacts.
  2. Consequence scoring and risk assessment (2nd workshop) – Qualitatively assessed the possible consequences of a climate hazard interacting with an asset. Workshop participants scored consequences using a consequence scoring system where “1” represents a very low consequence and “5” represents an extreme consequence.
    The likelihood and consequence scores were multiplied for each climate hazard-asset interaction to determine the level of risk across the three time periods (baseline, 2050s, and 2080s). High or extreme risks were identified and prioritized.
  3. Adaptation measures identification and prioritization (3rd workshop) – Workshop participants identified possible adaptation measures that could be applied to reduce the highest risks and prioritized the feasibility of implementation.

The CRRA assessed climate risks in the baseline, 2050s and 2080s time periods. The results show that the biggest shifts in risk levels (from low/medium to high) between the baseline and the future periods were due to projected increases in the frequency and severity of extreme heat events and severe storms. The assets likely to be at the highest risk in the future include street trees, humans, gardens/flower beds and trees. The highest-risk interactions include:

  • Severe storms could damage the structural integrity of trees.
  • Severe storms could result in injury to humans, especially vulnerable populations.
  • Severe storms could damage the structural integrity and function of assets in the built environment (e.g., street furnishings becoming airborne and electrical transformer boxes being impacted by lightning).
  • Short-duration, high-intensity rainfall events could flood sidewalks and roads, affecting the structural integrity and functionality of the streetscape.
  • Extreme heat events could impact asphalt surfaces, causing buckling and affecting the functionality and structural integrity of the surfaces. In addition, asphalt roads, parking spaces and existing buildings are likely to exacerbate the heat effect due to the heat-island effect and increase the risk of heat-related illnesses to humans and animals.
  • Extreme heat could affect the health and safety of users and workers (operations and maintenance) along Stephen Avenue.
  • Extreme heat could affect the structural integrity of the natural environment by causing heat stress (street trees, gardens, flower beds) and the health and safety of animals and pollinators.


After identifying and prioritizing the highest risks, the CRRA proposed 30 adaptation measures. City staff rated the proposed adaptation measures based on feasibility criteria for each measure’s practicality, equity, synergy, urgency, effectiveness, cost-efficiency, robustness, funding and foundational importance. Based on the criteria and staff feedback, the top recommended adaptation measures that could be applied to reduce the highest risks were identified and are as follows:

  1. Extensive planting of trees and other vegetation to increase shade.
  2. Create and maintain an emergency operation budget that can immediately be used for emergency response purposes.
  3. Plant trees with large canopy covers in areas with high solar radiation.
  4. Identify and update where necessary, design flood levels and ensure assets meet current flood predictions (pluvial and riverine.)
  5. Retrofit green spaces such as grassed center medians of roads with bioretention systems, street planters or tree-box filters.
  6. Develop heat/air-quality action plans (e.g., cooling centers, drinking water fountains/features).
  7. Use permeable paving and a sub-surface drainage system.
  8. Plant trees and other vegetation around roadways to lower the water table.
  9. Develop a management program to check drains, etc.
  10. Create gradients/borders of open areas and shading elements where sun and shade alternate.
  11. Create diversities of microclimates combined with park furniture.
  12. Development of management plans – updating operation and maintenance (O&M) procedures to check trees and plants after events.
  13. Reduce asphalt/hardscape spaces.

The construction budget available will determine how the project moves to implementation.

Outcomes and Monitoring Progress

The Stephen Ave Redesign Project publicly released the Conceptual Streetscape Master Plan design in late 2023, which is available online. Developing a robust Streetscape Master Plan is key to bringing the vision for Stephen Avenue to life. It will be a guiding document as the project moves into detailed design and construction. The Streetscape Master Plan is informed by the vision set in Phase 1, public feedback, and the CRRA to ensure that the design is implementable and climate-resilient.

In terms of the design and construction and the implementation of recommended measures, the move to include trees in the shared street (4th ST to 1 ST SE) is subject to utility relocation. While the project team still advocates for this, it will be subject to leadership decisions and funding availability. Trees from 11 ST SW to 4 ST SW do not require utility relocation, so they would more likely move forward should the project receive funding for implementation.

In addition to the trees, other moves included in the conceptual master plan which support the adaptation measures include:

  • Gradients/borders of open areas and shade where sun and shade alternate.
  • Diversity of microclimates combined with park furniture.
  • Bioretention systems and at grade planting.
  • Potential to integrate permeable paving.

The City is also removing vehicle lanes to focus on pedestrian and active mobility transportation modes. While not listed in our CRRA report, this is also contributing to climate goals.

Next Steps

Phases 3 and 4: Detailed Design + Construction are anticipated to begin in 2024. While this project is focused on physical infrastructure improvements, many of the other recommendations that came from the CRRA, such as management plans and operations and maintenance procedures, will be explored as part of a later stage of work.