The Risks
The Priorities
Wildfire risk to forest lands and homes is inseparable. Forest fires can endanger and burn homes. Fires that start as structural fires can quickly spread to the forest. Although the threat of wildfire is not as great in Clackamas County as in other parts of the state, wildfire officials are cognizant of the growing potential. One of the core elements of the Clackamas Community Wildfire Protection Plan (CWPP) is developing an understanding of the risk and potential losses to life, property, and natural resources during a wildfire to identify and implement the most effective strategies for preventing losses from fire, while allowing natural fires to take their course in shaping a more healthy and sustainable forest.
A large wildfire can pose a range of risks to the environment and the economy, the greatest risk is to life and property. A community survey during the development of the CWPP found that very few residents had created defensible space around their homes or had a personal evacuation plan.
Defensible space is a natural or human-made area in which material capable of supporting the spread of fire has been treated, cleared, or modified to slow the rate and intensity for advancing wildfire and allow space for fire suppression operations to occur. Research shows that investment in defensible space on private property is the most promising approach to reduce wildfire damage and suppression costs in Wildland Uraban Interface communities.
Wildfires can have long term effects on the economy and the environment, and though are working to insure the resiliency or our community and environment, or priority is insuring that every home has the best chance of surviving and that all residents can safely evacuate during a wildfire.
Geographic Overview
Clackamas County is in northern Oregon and consists of two significant Level III ecoregions: Willamette Valley and Cascades. The Willamette Valley ecoregion in the western part of the county is more populated, is lower in elevation and has lower precipitation (37 to 60 inches) than the Cascades ecoregion, and is composed of fluvial terraces and floodplains, scattered hills, buttes, and adjacent foothills. The Cascades in the eastern part of the county is less populated, higher in elevation, and has higher precipitation (50 to 125 inches) and is dominated by coniferous forests that is managed for logging and recreational use. The union of the two ecoregions increases the diverse nature of the Clackamas County landscape and can have unexpected consequences related to wildfire in the highly populated areas in the western portion of the county.
Historically, forests regularly burned, reducing the amount of dry woody debris and, in turn, reducing the severity of wildfires. Modern land and forest management practices, pursuing a fire suppression strategy, resulted in the buildup of forest vegetation, such as woody materials from brush and downed trees and limbs. The buildup of forest vegetation increases the intensity and severity of fire risk. This is particularly true in dry forests where fire regimes were historically “high frequency, low severity” but due to fire suppression over the past 150+ years, fuels have built up. Conversely, in wet forests fire is uncommon with long intervals between fire events and when fires do occur, they tend to be severe, like the 2020 Labor Day fires. Fire suppression over the past 150+ years has had less of an impact on fuel build up in wet forests because they are naturally abundant in vegetation and are typically too wet to burn except during extreme weather events. For example, a natural fire rotation for the wet forests of Bull Run, which are extremely wet and productive, was determined to be 350 years and the fire regime is “low frequency, high severity”. Because fires are not common in forests west of the Cascades, less is known about the effectiveness of dry-forest fuel reduction strategies in wet west side forests. The Pacific Northwest Quantitative Wildfire Risk Assessment (QWRA) classifies these fuels as a fire risk for nearby communities. Household structures and communities adjacent to or incorporated on public lands have a higher risk of wildfire than households in more urban areas.
As development continues to expand into rural and wooded areas, the cost of fire suppression, risk mitigation, and disaster planning needs to be accounted for and planned. More people are moving into undeveloped areas, thus increasing their risk of wildfire displacement. The updated CWPP accounts for this increased risk and addresses policy recommendations that will support greater funding opportunities for these communities. As communities continue to develop in the high-risk areas of Clackamas County, the cost of fire management and community preparedness will disproportionally put pressure on households living near wildland areas. Therefore, the CWPP update recognizes an imperative need to increase interagency cooperation, promote effective communication between agencies, and create a fire resilient Clackamas County.
Click the map to visit the Oregon Explore and view the Oregon Hazard Map
Determining Risk
Prospective priority mitigation areas for the county were mapped using a conditional classification method involving three layers: (1) Overall wildfire risk, (2) Wildland-Urban Interface (WUI) status, and (3) Social Vulnerability. The layers are overlapped and where the vulnerabilities intersect highlight critical areas.
Overall Risk
The Oregon Statewide Wildfire Hazard Map created by Oregon State University was used to map the overall risk to the county. The map considers the likelihood of a fire igniting and potential fire intensity(flame length) based on vegetation type to determine the risk to a structure in the area. In short, how likely is it that a fire will start and if it does, how intense will it be?
Wildland Urban Interface
The wildlife urban interface or WUI refers to the zone where human development (homes, businesses, infrastructure) meets or intermingles with undeveloped wildland or vegetative fuels. This area is characterized by the potential for conflict between human activities and natural ecosystems, particularly in the context of wildfires.
For the purpose of determining risk, Oregon uses a more specific definition of the WUI. Simply stated, it has average density of one structure or other human development per 40 acres and meets or mingles with wildland fuels.
Social Vulnerability
The overall vulnerability of people and property to wildfire is conventionally estimated using spatial distribution of the probability of exposure to wildfire hazard. The concept of social vulnerability adds depth to this estimate by additionally accounting for how and why some people are at a disadvantage in comparison to others due to personal, social, economic, or cultural characteristics which make them more vulnerable to harm from specific types of hazards such as wildfires.
The below table show an example how priorities areas are ranked. You can see that areas with a high wildfire risk, with a high social vulnerability in the urban interface are the highest priority.
Risk to Highly Valued Resources and Assets
The value of the asset as risk is also taken in to consideration when determining priorities. This is done by determining what is the potential loss if a wildfire occurs.
High Values At Risk included in the integrated maps include the following:
People and Property
Infrastructure
Timber
Drinking Water
Agriculture
Recreation Infrastructure
Ecological Integrity
Wildlife Habitat
The following integrated maps are included in at the bottom of this page.
Conditional net value change integrated across all HVRA (Map E-8)
Expected net value change integrated across all HVRA (Map E-9)
Conditional net value change for Drinking water (Map E-11)
Conditional net value change for People and property (Map E-10)
Conditional net value change for Timber (Map E-12)
Communities at Risk
The Healthy Forest Restoration Act guides the development and implimentation of CWPPs, and provides a definition for at-risk communities:
a group of homes and other structures with basic infrastructure and services (such as utilities and collectively maintained transportation routes) within or adjacent to Federal land in which conditions are conducive to a large-scale wildland fire disturbance event and for which a significant threat to human life or property exists as a result of a wildland fire disturbance event.
Different scales of Communities at Risk (CAR) are necessary to direct large-scale state and federal planning efforts as well as local outreach projects. The Clackamas CWPP addresses wildfire hazards county-wide (not just those areas near state or federal lands), including local CARs within each fire district.
Fire professionals considered the following factors to determine the local CARs:
Need for defensible space.
Access limitations (narrow driveways, lack of address signage, one way in/one way out).
Steep slopes that can hinder access and accelerate the spread of wildfire.
Lack of water available for wildland fire fighting.
Heavy fuels on adjacent public lands.
Potential ignition sources from recreationists and transients.
Agricultural and backyard burning.
Lack of community outreach/awareness.
Communication issues.
Though all CARs have some factors in common, they may also have unique wildfire hazards that must be addressed on the local scale. Communities that have been identified as being particularly vulnerable to wildfires are listed by fire district on the Communities at Risk page.
