Snohomish County Prepares for a Changing Climate
Snohomish County is experiencing a greater frequency of wildfires, wildfire smoke, intense storms, flooding, and extreme heat events. Addressing the effects of climate change and building community resiliency is vital for the overall health and longevity of our communities, businesses, and natural environment. Although we are all feeling the impacts of climate change, it does not impact us equally. Many residents lack access to resources or have existing physical conditions that make them exceptionally vulnerable and susceptible to climate impacts. Snohomish County Prepares for a Changing Climate provides a one-stop-shop to learn more about the risks we face, resources to provide you and your family relief, and ongoing County efforts.
Climate Vulnerability Tool
Screenshot of CVT
The Climate Change Vulnerability Tool (CVT) is a web map application that assesses climate change risks to Snohomish County communities. Reviewing the CVT will teach you about your local community’s vulnerability to climate change impacts and help you better prepare yourself and your loved ones.
Explore the CVT to view where areas or communities in the county might be more vulnerable than others to the impacts of climate change.
What is the combined vulnerability score?
The CVT assigns every single Census block group in the county with a Combined Vulnerability Score (CVS).
The CVS represents an area's vulnerability to climate change and all of its associated hazards, including wildfires, extreme heat, and flooding. You can think of the CVS like the height or weight percentile you get at the doctor’s office. For example, a Census block with a CVS of 62 is in the 62 nd percentile of climate vulnerability compared with all other Census blocks in Snohomish County.
The CVS is calculated from the average of three indicators:
Example of CVS and indicator scores for a census block group
- Adaptive Capacity Gap: The extent to which people, assets, or systems face barriers to adjusting to a hazard, taking advantage of new opportunities, or coping with change. The higher the adaptive capacity gap value, the lower the ability to adapt to potential climate hazards. Examples of this data include income, level of education, household size, and housing cost burden.
- Sensitivity: The degree to which a system, population, or resource is or might be affected by a climate change hazard. Sensitivity data sets include age, housing, and chronic health conditions such asthma and heart disease.
- Exposure: Projected climate change impacts (days of extreme heat, frequency of storms, sea level rise, risk of wildfire) by mid-century. A high greenhouse gas emissions scenario is used.
These values are then averaged for each Census block group within the County (total = 573 blocks) to determine the combined vulnerability score. The average CVS in Snohomish County is 42.
How is climate change impacting the county?
Extreme Heat
Extreme heat events – defined as days where the temperature is over 90 degrees – will worsen in Snohomish County as climate change continues. By mid-century the county is projected to experience between eight to 20 more days of extreme heat each year, which means increased calls for emergency services, hospital visits, and increased energy usage (Snover 2019) .
Graph 1 - This graph shows the overall trend of an increase in 90 degree days throughout the next century. Source: UW Climate Impacts Group
The map to the right depicts the projected increase in extreme heat, mapped to Census block groups across Snohomish County ( Phillips 2023 ). A higher extreme heat “score” means an area is more likely to experience more days of extreme heat as compared to all other areas of the county. This map is an example of the kind of exposure data that informs the climate vulnerability score, and is available in the Climate Vulnerability Tool .
Wildfire
Wildfires are becoming more common in Snohomish County. The 2022 Bolt Creek Fire burned across 14,000 acres and prompted evacuation warnings for communities in Index, Gold Bar, and Skykomish.
Homes and communities in or near forested areas are more at risk of experiencing damage or destruction caused by wildfires, and communities across Snohomish County are impacted by resulting smoke. There are approximately 130,000 residents who live in an area at high risk of a wildfire, meaning there is more than 50 percent burnable forests or grassland.
Graph 2 - Likelihood of wildfire in the county is projected to increase over the next century. Our maps use the 2030-2059 mid-century time period. Source: UW Climate Impacts Group
The map to the right portrays the increases in likelihood for wildfire in a future 30-year time period (2030-2059), mapped to Census block groups across the County ( Phillips 2023 ). A higher wildfire and smoke "score" means an area is more likely to experience conditions conducive to a wildfire as compared to all other areas in the county. This map is an example of the exposure data that informs the climate vulnerability score, and is found in the Climate Vulnerability Tool .
Intense Storms and Flooding
The county is home to several major river systems (Snohomish, Stillaguamish, Skykomish, Pilchuck, and Sultan) and flooding of streets, farmland, and property are longstanding issues. Costs to remediate flood damage are increasing. As recently as December 2023, a record-level flooding event occurred on the Stillaguamish River, reaching more than seven feet above flood stage at Arlington.
Change in the intensity of heavy precipitation events are more likely to cause flooding events than changes in seasonal and annual precipitation.
Graph 3 - An overall increase in the change in extreme precipitation is projected to occur this century. Our maps use the 2030-2059 time period. Source: UW Climate Impacts Group
The map to the right shows projected increases in precipitation by mid-century (2030-2059), mapped to Census block groups ( Phillips 2023 ). A higher extreme precipitation “score” means that an area has an increased likelihood of heavy precipitation during storm events by mid-century as compared to all other areas of the county. This map is an example of the kind of exposure data that informs the climate vulnerability score, and is available in the Climate Vulnerability Tool .
Who is most vulnerable to climate change in Snohomish County?
Some populations have characteristics that make them more susceptible to climate change and associated weather hazards. These characteristics can be classified by sensitivity and adaptive capacity indicators.
Sensitivity
Sensitivity is defined as the degree to which people or communities are affected, either adversely or beneficially, by climate change. Indicators of sensitivity include characteristics of a population, such as age and health conditions, that affect the degree to which the population is affected by potential hazards.
As an example, this map highlights asthma prevalence in adults (Source: CDC), mapped by Census block group. A higher score means that a certain area has more individuals who have asthma as compared to all other areas in the county. High scores are apparent in rural communities (near Granite Falls, Gold Bar, and Darrington), along the Highway 99 and I-5 corridor near Everett and Mukilteo, and in communities within and around the Tulalip Reservation.
This map is an example of the kind of sensitivity data that informs the climate vulnerability score, and is available in the Climate Vulnerability Tool .
Adaptive Capacity Gap
Adaptive capacity gap represents potential difficulties for communities, institutions, or people to adjust to climate-related hazards, take advantage of opportunities, and/or respond to consequences.
As an example of an adaptive capacity gap indicator, this map shows the percent of households per Census block group with no vehicle access, meaning they would have more difficulty responding to the consequences of a climate-related hazard, like a wildfire or flood. Communities clustered along Highway 99, as well as those in and around Stanwood in particular are impacted.
A higher score means that a certain area has more individuals who lack access to a vehicle as compared to all other areas in the county. This map is an example of the kind of adaptive capacity gap data that informs the climate vulnerability score, and is available in the Climate Vulnerability Tool .
Resiliency and engagement resources
Snohomish County and our partners have a variety of resources to help members of the public, property owners, and business owners build resiliency, mitigate climate risks, and get engaged with climate planning. Explore available resources and plans below and spread the word among your friends, family, and neighbors.
