Novel analysis of existing risk assessment data: Evaluation of plausible future community wildfire disasters in western Oregon and Washington

Project Description

Maximum exposure potential (based on simulations) illustrates the relative magnitude of maximum building exposure that could result from an ignition at the given location. Exposure values binned in quantiles so the “Very Low” category accounts for pixels with the bottom 20 percent of exposure values and the “Very High” category includes all pixels with the top 20 percent of exposure values.

Maximum exposure potential (based on simulations) illustrates the relative magnitude of maximum building exposure that could result from an ignition at the given location. Exposure values binned in quantiles so the “Very Low” category accounts for pixels with the bottom 20 percent of exposure values and the “Very High” category includes all pixels with the top 20 percent of exposure values.
Each year, wildfire related losses outpace the resources available for mitigation and adaptation. Seeking information to address this conundrum, policy makers sometimes turn to the rapidly advancing field of wildfire risk science. In the Pacific Northwest, recent wildfire risk assessments generally illustrate low risk to west-side forests and communities compared to elsewhere. However, as the events of 2020 confirmed, this region is vulnerable to extremely consequential wildfires, albeit infrequently. It can be challenging to characterize and communicate the risk of these very rare but impactful events, and standard risk assessment outputs are generally not as good at accounting for them. Therefore, in this project researchers used a novel analysis approach to explore where community wildfire disasters are plausible.

Image: Maximum exposure potential (based on simulations) illustrates the relative magnitude of maximum building exposure that could result from an ignition at the given location. Exposure values binned in quantiles so the “Very Low” category accounts for pixels with the bottom 20 percent of exposure values and the “Very High” category includes all pixels with the top 20 percent of exposure values.

Purpose and Scope

The primary purpose was to illustrate a relatively novel approach to characterizing wildfire risk to communities in landscapes exposed to low-probability, high-consequence wildfires. This new analysis can be used to better understand unlikely scenarios, plausible surprises, and disasters. The analysis includes communities in western Oregon and Washington. 

Methods

We used simulated wildfire perimeters generated as part of a 2018 quantitative wildfire risk assessment and intersected the simulated fires with building locations in order to measure plausible community wildfire exposure. Specifically, we evaluated potential wildfire disasters where more than 100 buildings were exposed. Simulated disasters were compared to historical disasters to determine whether the simulations provide novel insight into community vulnerability.

Key Findings

• While only a handful of communities have experienced historical disasters, nearly 50 percent of communities are vulnerable to future disasters.
• When comparing historical events with model simulations, we found that the magnitude of plausible future disasters exceeds any recent historical events.
• Results indicate that ignitions on private land and adjacent to communities are most likely to result in large numbers of buildings impacted by wildfire.

Image: (A) Maximum historical community exposure; (B) Maximum simulated community exposure; and (C) The difference between simulated and historical maximum community exposure events. In panels A and B, labeled communities are the five communities with the greatest maximum exposure values. In panel C, labels corresponding to areas mapped as blue indicate the communities where historical exposure exceeded simulated maximum exposure.