Research defines most fire-prone areas in state
When it comes to wildfire, you don’t necessarily vie to be No. 1. But in a study of wildfire risk in Washington, of the 10 communities at highest risk, seven are in Okanogan County. The town of Methow is in first place, Winthrop comes in at No. 6, and Twisp is No 7.
The worrying predictions are in a study conducted last year for the U.S. Forest Service by the Montana-based research firm Pyrologix.
“Exposure of Human Communities to Wildfire in the Pacific Northwest” looked both at the likelihood of a wildfire and the number of housing units directly exposed to fire risk based on location. Because the researchers analyzed risks based on the location of the community and the location of its residences — rather than the cumulative risk for all houses — the risk doesn’t necessarily increase just because there are more houses, they said.
Researchers defined a community as the population, or housing units, within a community core, plus the population within a 45-minute drive. Neighboring communities were classified separately.
“It is important that readers focus less on the exact ranking number, but rather on the broader message,” said Rick Stratton, a co-author of the study and a fire analyst with the U.S. Forest Service.
“The greater Okanogan-Wenatchee Valley is a very fire-prone environment. From the simulation modeling it gives rise to the most large fires in the Pacific Northwest. Although we have had several really large fires over the past eight or so years, there is still a lot of landscape left to burn and some of it is near communities,” said Stratton by email.
Researchers used a technique that simulates wildfire behavior using 10,000 or more iterations to determine the annual likelihood that a wildfire will reach a given point on the landscape. The model also allows them to chart the origin point and final perimeter for each simulated wildfire, enabling them to establish the risk for an individual house.
There are two ways for a community to be ranked as highly exposed to wildfire — either by high likelihood or high population. The researchers plotted these risks on a graph that goes from a high number of houses with little chance of burning, to a moderate number of houses facing a high probability of fire. Those facing a high risk — which include Twisp, Okanogan and Tonasket — are candidates for interventions to reduce wildfire exposure near homes, said the researchers.
Researchers assigned a mean annual-burn probability rank for housing units. That predicts that 303 housing units in Methow are exposed to wildfire, 1,095 in Winthrop, and 1,364 in Twisp. The other Okanogan County communities in the top 10 are Riverside, Disautel, Conconully and Malott. North Omak and Pateros are Nos. 20 and 21 for overall risk, and Tonasket is No. 28.
The burn probability relates to the likelihood that a wildfire will reach a given housing unit, said Joe Scott, principal wildfire analyst for Pyrologix and lead researcher for the study. That’s different than being threatened by a nearby wildfire, needing to evacuate, or being affected by smoke, he said by email.
The data also paint a picture of community-wide exposure, which does increase with the number of housing units. Using that metric, Tonasket has the eighth-highest overall community exposure, Omak is 10th, and Twisp is 11th. Mazama is not listed separately. Because community exposure takes into account the total number of housing units at risk of wildfire, areas with a larger population like Spokane and Wenatchee made it into the top 10 for community risk.
One application of this research is to help mitigate fire danger, said the researchers. Governments and other organizations can use the data to prioritize interventions such as Firewise programs that create defensible space. They can also use the information to develop appropriate building codes and plan areas suited to residential development.
Property owners and land-management agencies can use the findings to identify areas where destructive wildfires are more likely. Prospective buyers can use the research to compare relative fire risk in different communities, according to the study.
A relatively small number of houses in Washington — about 264,000 — face a high risk of wildfire. The researchers found that the 50 communities most exposed to wildfire contain only 12 percent of Washington’s 2.2 million housing units — but these communities account for 70 percent of the risk of wildfire.
The researchers performed the same analysis for Oregon. The likelihood of a fire in Methow is so high that the town still comes out as No. 4 in a list of risks in Washington and Oregon combined. On that list, Winthrop is No. 10 and Twisp is in 11th place.
At the other end of the scale of 627 communities in Washington are several towns in the Puget Sound region, including Seattle at No. 612.
“The main goal of the project is to identify areas that are most likely to burn AND are adjacent to things we care about — in this case homes — and try and get ahead of it and mitigate the loss,” said Stratton by email. “BUT, the fire problem is too big for a single agency, we need everyone to assist — and I mean everyone. Each of us from the homeowner (especially), to city, county, state, private and federal must each do our part in our own sphere of influence — collaboratively — to have the greatest chance of success.”