An analysis of the Labor Day 2020 wildfires in Oregon determined that the combination of high temperatures, unusually dry fuels, and strong winds occurring at the same time was unprecedented in the area.
That flammable combination led to an unprecedented number of acres burned in the Oregon Cascades, about 11 percent of the mountain range, and more than the previous 36 years combined.
Below is a summary of research published last month titled, “Compound Extremes Drive the Western Oregon Wildfires of September 2020,” by John T. Abatzoglou, David E. Rupp, Larry W. O’Neill, and Mojtaba Sadegh.
“Several very large fires in western Oregon spread rapidly during an unusually strong offshore wind event that commenced on Labor Day in 2020. The Labor Day fires burned more area of the Oregon Cascades than had burned in the previous 36 years combined and very likely exceeded the area burned in any single year for at least the past 120 years. The fires damaged over 4,000 structures, led to several fatalities, placed over 10% of the state’s residents under some level of evacuation advisory, and contributed to the hazardous air quality across the Northwestern United States.
“A compound set of weather-related factors leading up to and during the fires facilitated these extreme fires. Unusually warm conditions with limited precipitation in the 60-days leading up to the fires allowed for fuels to become particularly dry and combustible by early September. Downslope offshore winds materialized during September 7–9, 2020 across the Oregon Cascades bringing exceptionally strong winds and dry air that drove rapid rates of fire spread. While neither of these individual factors was unprecedented, the concurrence of these drivers created conditions unmatched in the observational record.”
The authors called that the “Plain Language Summary.” To drill down even more into Plain Language, the conditions in Oregon were hot, dry, and windy.
The Hot-Dry-Windy Index (HDWI) is a new tool for firefighters to predict weather conditions which can affect the spread of wildfires.
It is described as being very simple and only considers the atmospheric factors of heat, moisture, and wind. To be more precise, it is a multiplication of the maximum wind speed and maximum vapor pressure deficit (VPD) in the lowest 50 or so millibars in the atmosphere. It does not consider fuel moisture.
In preliminary data that had not been peer reviewed when we wrote about it February 20, 2019, the HDWI was far more useful than the Haines Index in predicting the growth of the Chetco Bar Fire which burned over 191,000 acres in Southwest Oregon in July, 2017.
The HDWI for Oregon’s Willamette Valley was far above the 95th percentile September 6-9, 2020. During the 10 days prior to September 9 it was above the 90th percentile on nine days. The strong winds occurred September 7-9, and most of the growth of the Labor Day fires was during that period.
Thanks and a tip of the hat go out to Bob.
Here is the 15-minute presentation I gave on western Oregon fire history to regional NOAA and AMS groups earlier this month. Presentations were limited to 15 minutes, including Q&A, in large part because the annual meeting was being held on Zoom and the entire program was compressed to 1/2 day.
My presentation begins at 4:09 and my conclusions were not — and have not (so far) — been questioned or otherwise challenged by the career meteorologists and climate scientists that participated in this event: https://youtu.be/aVSnCs9LxeY
Bob,
Would you make any comparison to oregons east wind fire events to californias santa annas.
Both are prevailing east phoen winds…correct?
Hi Vean: Yup. The main differentiation is fuels. Douglas fir in western Oregon and shrublands in southern California.
Two of the authors are based at OSU. The paper specifically refers to western Oregon wildfire history and weather patterns. I continue to find it very odd that my 2003 PhD dissertation at OSU dealing with these very same topics continues to be ignored by the current research community. There are a few misleading and inaccurate statements in this paper that could have easily been corrected if the authors had only done a reasonable “literature review,” as incoming freshmen are taught. These weather conditions were NOT unprecedented and EVERY major western Oregon wildfire during the past 220 years took place on an east wind. The problem was/is mismanagement of federal forestlands and has little or nothing to do with unusual weather or a “warming climate”: http://nwmapsco.com/ZybachB/Thesis/Zybach_PhD_2003.pdf
Is this the same “Frank Carroll” who works for wildfirepros?
May rainfall on the Oregon South Coast is .75″. This is 1/10th the total of May 2020.
Dear Frank
The August Complex was on the Mendocino. The North Complex was on the Plumas. I was on the North Complex essentially from beginning to end. I ran several divisions and was in constant contact with the operations section. During that time never once was “managed fire” ever discussed. 100% full suppression with every resource we could get. So don’t worry about tallying any North Complex acres into your little equation bud.
We need an honest accounting of the percentage of acres burned on purpose to meet “managed fire” objectives, how many acres were lit by fire crews, and how many miles of fireline was constructed indirectly for the purpose of big boxing these fires. I know that the fire situation was dire and that weather and fuel played a huge role. I also know that several of the fires, from California to Oregon, were not attacked in the early stages because of the amorphous and aspirational objectives of “using unplanned fire in the right place at the right time” to “reintroduce fire to fire-depleted ecosystems. (Victoria Christensen 2019) “Restoration wildfire” has become a religion. The issue is that no one is keeping track of the cumulative impacts of these fires on timber outputs, range condition, site conversion, and other key elements that would tell us if our “managed fire” paradigm is doing good or doing harm. The Plumas National Forest essentially burned to the ground as a result of “managed fire” in the early stages of the August Complex.”
Frank, why didn’t the Plumas aggressively attack the August Complex? There has to be some logical reason the Plumas didn’t put it out while it was small.
Frank, how many fires were started all at once after that lightning bust. I can assure you that NO fire went into a managed status when they started. Just because in 2019 they said they wanted to manage some fires doesn’t mean they did it when 100s ignited at the same time. Additionally, with a heavy draw down of resources it was probably insanely hard to staff all of those fires. Be a part of the solution if you have better ideas. Also, the August complex wasn’t on the Plumas. Derp.
Frank,
Your right on. The August Complex and several of the fires in 2020 are classic examples of what happens when the Forest Service and BLM try to implement the un-written, unproven, managed fire concept. I have asked for years if they were ever going to do a post fire analysis, on what the conditions of the landscapes were after the fires in terms of ecological effects and the risk of more destructive fires in the future. People just need go look at the result of this failed policy. !
Roger Jaegel
Correction. I am referring to the North Complex, not August Complex.
Wow frank, just going to spit a bunch of diarrhea out of you mouth and only correct yourself on the fire you were talking about? Why don’t you tell us young folk how your generation would have gone in there direct. Tell all those crews that were understaffed they shouldn’t have burned off those roads to try and get an edge when we had a fire make a 100,000 plus push in one day. I’m assuming you sit high on your horse watching the devastation as a “wildfire expert witness ” in your made up position collect checks and Monday morning quarterback forest management. Can we do better management forest? Sure. But to think those folks are out there letting fires burn for hundreds of thousands of acres for resource benefits is plain dumb.
Can you explain how anyone with knowledge of wildfire in this Forest type would start a large aerial ignition in the face of a certain Northeast wind event that was predicted for days not to mention severe drought conditions, extremely low humidity and fuel moisture.
Spent 8+ weeks on the North Complex. At no point was “managed fire” mentioned, discussed, or considered. I am 95% sure that “managed fire” is not included in the current Plumas FRMP. I must have missed you in the OPS tent or, perhaps, you were never there.