Excerpt from the AWC Climate Resilience Handbook

Adaptation strategies generally focus on risks associated with climate- influenced events and a changing environment. These events can have dramatic impacts on public health and safety and pose a threat to human life, infrastructure, and property. Such events can significantly impact city budgets for operations, capital, and infrastructure.

Fortunately, most of these events can be anticipated and planned for. Data and information identifying risks are readily available and frequently updated. These data should serve as an essential platform for adaptation planning and emergency preparedness.

Assessing risks involves first identifying risks for a city, and then analyzing potential impacts over time using best available science. The University of Washington Climate Impacts Group (CIG) suggests three key components needed to accomplish this:

• Educate: Raise awareness and understanding of climate risks by educating key decision-makers.
• Analyze: Use science and local information to assess risks and likely climate impacts that matter to your city.
• Act and adjust: Take multisectoral, adaptive, responsive, and flexible actions to manage and address those risks, then learn and adjust as needed.

For example, a city assessing risks from sea- level rise would likely follow these steps:

• Identify the risk. Based on best available science, projected sea-level rise is expressed in terms of probabilities. Scenarios range from approximately 8 inches to approximately 2 feet by 2050, and they vary for different locations in the state. The low and high estimates are low percentage probabilities on either end of a bell curve. However, the middle range at the top of the curve—1 foot of sea level rise by 2050—has a 50 percent probability.
• Identify risk variables. Based on best available science, what factors might modify sea-level projections for your city? Factors to consider include soil uplift or subsidence, flooding, or estimations of tidal influences that may impact severity of risk and local variability.
• Identify what is at risk, and develop response scenarios. What is at risk from sea-level rise in your city (e.g., population centers, parks, beaches, water or wastewater treatment facilities)? What does the science reveal regarding worst-case scenarios, such as king tides during flooding and storm events and the estimated timing of such events? What are the scenarios, options, timing, and costs for responding?
• Formulate and implement a response. What operational, regulatory, and/or capital measures will be considered and taken, and how will they be paid for? What emergency planning is required? How will decision-makers and the public be educated and informed?
• Monitor and evaluate the efficacy of the response and evolving climate risks. Update response as necessary, incorporating the best available data and information.

These five steps are generally applicable for assessing and responding to all of the risk factors associated with climate change. Please note that risk factors are dynamic; it is essential to integrate best available science into this work and to monitor and update these efforts.

Local flooding and associated landslides will occur more frequently and will factor into future pareparedness for cities.

What follows is a description of two common types of risks and challenges associated with a changing climate and climate-influenced events.

Surface water management

Increasing frequency and intensity of heavy rainfall events will require additional surface water management capacity. Such events are projected to increase under all climate scenarios, particularly for areas west of the Cascade Mountain range. According to the NCA-24 (see “Primary Source,” at right), “Average winter precipitation is expected to increase . . . and extreme events, like heavy rainfall associated with atmospheric rivers, are also anticipated to occur more often.”

In response to surface water challenges, cities are incorporating nature in the form of “green infrastructure” or “green and gray” infrastructure. Such approaches incorporate nature-based solutions with more traditional engineering approaches.

Green infrastructure strategies can complement legacy systems, taking some of the burden off of pipes, pumps, and treatment facilities. These systems—such as bioswales, rain gardens, permeable pavements, green roofs, infiltration planters, and rainwater harvesting systems—can also provide additional water resources and can be designed to meet different needs. At larger scales, the preservation and restoration of natural landscapes such as forests, floodplains, and wetlands are also critical components of green infrastructure.

Flooding and landslides

As climate changes, snowpack decreases, and heavy rainfall events become more frequent, local flooding and associated landslides will occur more frequently and will factor into future preparedness for cities. Areas with streams, drainage, slopes, and soil profiles indicating potential instability and greater risk should be monitored, particularly during periods of intense rain events.

The geology of the Pacific Northwest is complex, shaped by plate tectonics, volcanoes, and glacial recession. Different geological areas or zones are more prone to landslides resulting from slope failure, mudflows, debris flows, and rockfalls.

Much of the state, and in particular western Washington, is characterized by layers of sediment including sandy soils, clay, and gravel. When soils become saturated due to rain and storm events, the moisture serves as a lubricant. The layers of soil become less stable and more susceptible to slope failure, leading to landslides.

Rainfall events are projected to increase in frequency and intensity, bringing periods of heavy precipitation. These events will result in increased flooding and saturated soils, contributing to more frequent landslides. The risk of landslides can increase even further after fire events where vegetation and root systems have been damaged, reducing soil and slope stability. Landslide risks can have major impacts on development and infrastructure such as roads and railways.

AWC’s recently released Climate Resilience Handbook provides basic information, resources, references, and examples regarding climate change and climate action planning, as well as hazard mitigation planning due to climate change. Find it at wacities.org.