The Caldor Fire and the Impact of Forest Management – Part Two: Models Predicted Extreme Fire Behavior for El Dorado County

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This article is Part Two of my series examining how forest management in previous years impacted the earliest days of the Caldor Fire. Part Two explores forest services modeling which accurately predicted extreme fire behavior across the Grizzly Flats region. Consider supporting the author so this work may continue by subscribing now.

It’s December 2014 and the Eldorado National Forest (ENF) service is working to select a plan to thin and treat over 20,000 acres of woodland.

Two years earlier the ENF determined forest to the southeast of Grizzly Flats to be unhealthy, overgrown, and dangerous. As I previously reported, the ENF had proposed The Trestle Forest Health Project (TFHP), a multi-year project to reduce fuel loads and repair access roads across miles of unmanaged forest. After securing community support and government funding, the ENF is examining options to determine the most efficient and effective way to complete the project.

One of the first steps to determine how best to reduce fire danger to communities surrounding the forest is to conduct a Fire and Fuels Analysis. This analysis will then be presented as part of the ENF’s Environmental Impact Statement. The goal of the Fire and Fuels Analysis is to understand the fire hazard and ignition risks across the project area. The 56-page report examines what would happen to the forest and surrounding communities if a fire ignites in one of several locations across the project area.

Early in the report, the authors note the rugged terrain and the difficulty accessing several areas across the forest in the event of fire. Without drastically reducing fuel loads, any fire within the forest here would be exceedingly difficult to contain.

The report also includes pages upon pages of alarming numbers. Over 78% of the TFHP area contains high fuel loads likely to produce flame lengths greater than four feet. 71% of the project area would produce flame lengths of over 11 feet. Flame lengths greater than four feet generally force firefighters to move back to safer zones where they then begin more indirect firefighting methods.

Over 70% of the project area “has the potential for high severity fire,” the authors write. 76% of the area is likely to produce crown and passive crown fire activity, and over 55% of the area has the “potential for rate of speed that would force firefighters to back off to ridge tops and implement indirect suppression tactics.”

The report then goes on to highlight Grizzly Flats, one of the most at-risk communities for wildfire in the nation according to the USDA. In addition to the ENF’s responsibilities for protecting this community, the report details how Grizzly Flats is also responsible for protecting itself. As such, the authors examined what the community had done up until this point to protect its residents and determined, “The Grizzly Flat Fire Safe Council is one of the most active councils in El Dorado County. Their active participation as a community to reduce fuels in and around the community has been an example to the rest of the nation’s communities at risk.”

In other words, the Grizzly Flat community has done everything in its power to reduce the threat of wildfire to its residents. Now, it’s time for the ENF to reduce the possibility that wildfire ever reaches the community in the first place.

The report then moves into computer modelling which places five hypothetical ignitions across the region. The models examine how fire would behave if the TFHP’s forest thinning is not completed. One of the locations chosen in the ENF’s models is Dogtown Creek. The hypothetical location is not far from where, years later, the actual Caldor Fire begins.

Without treatment, the report says, a light, southerly wind would push the fire north into heavy fuel loads. From here extreme fire behavior, unmanageable flame lengths, and a high rate of spread would be likely. Should a fire occur in this area, “few opportunities” exist to reduce fire size and intensity if the forest had not been previously thinned, according to the report. In fact, depending on wind directions several models bring extreme fire behavior to Grizzly Flat in just days following the hypothetical ignition in Dogtown Creek. The extreme nature of the fire means firefighters would have few opportunities to directly attack the flames.

However, following forest treatment from the TFHP, firefighters would at least be afforded the opportunity to “go direct” on the fire. This is because, while the fire would still spread to the north given a light southern wind, fire intensity, flame length, and the forward rate of spread would all be greatly reduced. In short, the report says, as long as the TFHP is complete firefighters would have the opportunity to slow, redirect, and possibly even contain any fire starting in the Dogtown Creek and Cosumnes River drainage system.

The report then examines which option to complete the TFHP would be most effective and efficient, concluding that Alternative 2 is the obvious choice: “Alternative 2 would be the most effective at reducing fuel loading on the greatest area of the Trestle project therefore reducing the likelihood of high severity fire across the landscape and adjacent to the community of Grizzly Flat…Fuel treatments mid-slope and lower slope positions help to reduce the rate of fire spread and flame lengths before the fire reaches the ridge tops allowing fire fighters more time to plan and implement suppression strategies.”

Finally, the report specifically details why Alternative 5 should not be chosen. The report reads, “Alternative 5 is also effective at changing the threat and severity of a wildland fire on the landscape. However under Alternative 5, fewer acres would be treated therefore the effectiveness is less than that of Alternative 2.”

After the Environmental Impact Study is published, which includes the Fire and Fuels Analysis, the ENF officially chooses Alternative 5. By July of 2021, only a fraction fuel-reduced acres under even this, the least ambitious option, is complete. One month later, Grizzly Flat would be destroyed by the Caldor Fire.

In future installments of this series we will examine what led to the reduction in completed acres as well as the challenges and delays the ENF faced in getting the TFHP off the ground.

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