USFS research confirms most CA fires occur in areas of WUI with sparse or no vegetation, but more people

Photo by LA Times

This morning I got an email from U.S. Forest Service Research News, which including a link to this new research from the USFS and partners concerning wildfires in California.

While the research may be surprising to some, it’s not at all surprising to many of us who have said the same thing going back a few decades now. We’ve had perhaps over a hundred debates about this on the blog over the years. Heck, Dr. Jack Cohen’s research documented much of this going back into the 1980s, if not even earlier. Richard Halsey and his California Chaparral Institute have been also talking about these issues for at least 20 years. And those of us who’ve been branded as “environmental terrorist groups” – and blamed for California wildfires by the likes of former Interior Secretary Ryan Zinke – have been also trying to get the public and policy makers to understand the dynamics at play for decades as well.

Remember, it’s been very common for politicians from through the country (but especially the West) to use wildfires in California as the reason why we need to dramatically increase logging on our public lands by systematically weakening bedrock environmental laws. While that may make for good politics when people turn on their TV’s and see flames, it doesn’t make for good policy that will protect communities, firefighters and save lives and money.

Most California Fires Occur in Area of Wildland-urban Interface with Less Fuel and More People

Madison, WI, September 24, 2019 – In California, the state with more building destruction by wildfire than all of the other states combined, new research by a U.S. Department of Agriculture Forest Service scientist and University of Wisconsin-Madison partners found something surprising. Over nearly three decades, half of all buildings destroyed by wildfire in California were located in an area that is described as having less of the grasses, bushes and trees that are thought to fuel fire in the wildland-urban interface, or WUI.

The study by H. Anu Kramer with Forest Service scientist Miranda Mockrin and colleagues, “High wildfire damage in interface communities in California,” notes that a portion of the WUI defined as “interface” and characterized by having more homes but relatively little wildland vegetation experienced half of the building losses due to wildfire but composed only 2 percent of the total area burned by the wildfires assessed in the study. The study was recently published in the International Journal of Wildland Fire and is available at:

California’s expansion of housing within and adjacent to wildland vegetation is not unique; the most recent assessment shows that the WUI now includes about one-third of homes in the United States. As wildfire management has become more complex, costly and dangerous, defining what constitutes WUI and defining more specific types of WUI has become more important as local communities strive to apply resources and policy-decisions where they will be most effective in saving lives and property.

The Federal definition of WUI describes two specific areas: “interface” WUI includes developed areas that have sparse or no wildland vegetation, but are within close proximity of a large patch of wildland. “Intermix” WUI, on the other hand, is defined as the area where houses and wildland vegetation directly intermingle. Both are separate from “rural” areas, which may be characterized by agricultural land and low-density housing and development (less than 1 house per 40 acres).

“Our findings show that WUI areas do experience the vast majority of all losses, with 82 percent of all buildings destroyed due to wildfire located in the WUI,” Mockrin said. “We were surprised to find 50 percent of all buildings lost to fire being destroyed in the interface portion of the WUI, however. Many risk reduction plans focus on natural vegetation fueling fire, but in the interface WUI where so much of the destruction is occurring, we have to consider finer-grained fuels such as wood piles, propane tanks, and cars.”

Study findings suggest that wildfires are still rare in urban areas. The Tubbs fire that struck Santa Rosa, Calif., in 2017 was similar to other California wildfires in that the majority of buildings lost in the fire were located in the WUI; however, the Tubbs Fire was unique in having 25 percent of all destruction occurring in urban areas. In comparison, 4 percent of destruction occurred within urban areas in other California fires. Other recent and highly destructive fires, including the 2018 Carr, Camp and Woolsey fires, included no urban area within their perimeters, exemplifying the rarity of the Tubbs’ building destruction in urban areas.

“Although the Tubbs fire was not the norm, it seems like every fall there is a new record-setting fire in California, with three of the five most destructive fires in state history having burned in the last 5 years and the deadliest California fire (the Camp fire) burning last year,” Kramer said. “These fires are fueled by the homes themselves, landscaping, and other man-made fuels that are seldom included in the fire models that are used to predict these fires. Our work highlights the importance of studying and mitigating the fuels in these interface WUI areas in California where most of the destruction is occurring.”

In addition to solidifying definitions of interface and intermix WUI so communities can address their different attributes in wildland fire planning, researchers suggest that fire behavior models should be revisited.

The study was co-authored by Volker Radeloff of the University of Wisconsin-Madison and Patricia Alexandre of the University of Lisbon.

10 thoughts on “USFS research confirms most CA fires occur in areas of WUI with sparse or no vegetation, but more people”

  1. Many serious California fires were ignited outside of the WUI. The Sobranes Fire, the Rim Fire, the King Fire, the Carr Fire and the Camp Fire (and more!) all started away from cities. Pretending that such fires weren’t significant or problematic is pure ignorance. It also appears that some people don’t want fuels projects close to towns, like we saw in the Camp Fire, on private timberlands.

    Also, I wonder how much it would cost to mitigate fuels problems near power lines, compared to just shutting off power several times each year. Of course, stupid humans cause way more wildfires than power lines. Remember, over 84% of all US wildfires are human caused.

  2. I thought it was kind of funny that they mention cars and propane tanks.

    ” but in the interface WUI where so much of the destruction is occurring, we have to consider finer-grained fuels such as wood piles, propane tanks, and cars.”

    That’s similar to things I’ve written about why running fires through communities is not considered a good idea by people in the communities. I pointed out that keeping houses from burning is not all the infrastructure that needs to be protected, and that people don’t like being evacuated and evacuating their livestock and companion animals.

  3. A picture worth a thousand words, and a good example of what this post is about. This fire just broke out a couple of hours ago.

    A large brush fire erupted in Simi Valley early Wednesday and was quickly burning toward neighborhoods, triggering mandatory evacuations amid strong Santa Ana winds.

    The Easy fire, which is burning along Tierra Rejada Road, started near the 118 Freeway and Madera Street shortly after 6 a.m. About 250 acres burned in the first hour, said Ventura County Fire Capt. Brian McGrath. More at:

  4. Research also confirms that there are more severe fires where there are more stupid people. However, stupid people DO leave the WUI and start fires elsewhere. Remember, over 85% of all US wildfires are human-caused. Preserving out-of-balance forests in advance of probable wildfires is just dumb but, I guess it fits in with our current society.

    The Kincaid Fire started out in the boonies, where there are no fuelbreaks or thinning projects. A lack of fuelbreaks and thinning on private lands also seems to be a recurring theme in fires that burn homes.

    • “Northern California was battered Sunday by extreme Diablo winds. The National Weather Service clocked a gust of 96 mph in the Mayacamas Mountains northeast of Healdsburg, which is threatened by the 54,000-acre Kincade fire that has destroyed 94 structures.” Source:

      “The area around the Kincade fire saw severe fire weather with sustained winds of roughly 50 mph and gusts as high as 76 mph overnight and Thursday morning, said National Weather Service meteorologist Matt Mehle. Temperatures around midnight were about 70 degrees, and humidity levels were about 10% to 15%.” Source:

      What type of fuel breaks or thinning would be needed to effectively deal with “sustained winds of roughly 50 mph” and wind gusts 76 to 96 mph?

      • No fuel break will ever stop something like that. It could help save lives by decreasing fire intensity in an area, say along a road, if circumstances are such that people are trying to escape a fast moving fire and not facing intense flame lengths in close proximity. Lots of ‘ifs’ in that sentence, admittedly.
        Thinning, if done in places that have a lack of recent (pick your time frame, but say 20-50 years) of fire history, or in the case of timber [not present in the ecoregion like in the Sierras or Rockies] where plantations never received appropriate thinning to remedy stupid dense stocking levels, may, *some* people would argue, reduce fire intensity, and perhaps reduce the sheer volume of flying embers ahead of a fire front, decreasing a risk to igniting homes.

        • Of course, I was very careful not to say that thinning and fuelbreaks would stop such a fire but, it is a curious fact that many of these fires on private lands (or non-government lands) never run into fuelbreaks or thinned forests. Similarly, most of the Fire-safe rules and laws are not enforced.

          Fuelbreaks give firefighters other options, sometimes. When the winds die down, as we have seen on the Kincaid Fire, firefighters can strategize maximum containment opportunities safely. (Keyword: safely) I think we’ll start seeing more of that kind of work in these fire risk zones. Same for the power line corridors. The public here is reaching a boiling point with both the fires and the blackouts.

          • Noted, sorry if I implied that in my comment. And two things come to mind – it is true that after more destructive wind driven fires, fuel breaks and thinned or treated areas can let firefighters get a hold on things, quickly, safely.
            Second, and most importantly – “..most of the Fire-safe rules and laws are not enforced”. That is so important. We need to switch the publics mentality that “Fires only happen to others”, and instead make it that fires can happen to almost anyone anywhere – Be ready!

  5. The President of the United States is at it again, threatening to cut off funding for American citizens who are suffering a disaster simply because the disaster and the people suffering happen to be residents of California. Apparently, the President of the U.S. thinks that all American citizens who live in California are Democrats, as if that would give him the right to threaten American citizens who are living through a disaster.

    For whatever it’s worth, as of 2019, of all registered voters in California 43% are registered Democrats and 24% are registered Republicans. In the 2016 presidential election, nearly 1 out of 3 people voted for Donald Trump. Apparently none of these American citizens living in California who voted for Trump have suffered from any disaster.

    The President of the United States took to Twitter this morning – as American citizens were afraid, scared and coming together to try and cope with a disaster – and said:

    The Governor of California, @GavinNewsom, has done a terrible job of forest management. I told him from the first day we met that he must “clean” his forest floors regardless of what his bosses, the environmentalists, DEMAND of him. Must also do burns and cut fire stoppers…….Every year, as the fire’s rage & California burns, it is the same thing-and then he comes to the Federal Government for $$$ help. No more. Get your act together Governor. You don’t see close to the level of burn in other states…But our teams are working well together in………putting these massive, and many, fires out. Great firefighters! Also, open up the ridiculously closed water lanes coming down from the North. Don’t pour it out into the Pacific Ocean. Should be done immediately. California desperately needs water, and you can have it now!

    According to the Los Angles Times (which the President of the United States has called “the enemy of the people” [even as some people have recently killed journalists in America, shooting up news-rooms and attempting to blow up members of the media by mailing bombs]):

    Trump threatens funding for California forest fires that didn’t happen

    –The most destructive fire broke out in the heart of Los Angeles’ Westside, starting just off the 405 Freeway near the Getty Center and burning 12 homes in Brentwood.

    –The Easy fire, which threatened the Ronald Reagan Presidential Library, occurred in a suburban area dotted by subdivisions and open spaces in Ventura County.

    –The Maria fire burned on a mountain amid citrus and avocado groves between Santa Paula and Somis.

    –The 46 fire occurred in a riverbed in Riverside County, the result of a car crash at the end of a high-speed police pursuit. The fire leaped from the riverbed to a nearby shipping container manufacturer.

    –The Hillside fire did begin at the edge of the San Bernardino National Forest. But it quickly burned downhill into a San Bernardino neighborhood, which is where the fire fight occurred. It ended up burning just 200 acres but destroyed several homes.

    Let’s also remember that last year, Interior Secretary Ryan Zinke came to California and blamed wildfires on “environmental terrorists groups.”

    i have a history degree, and my grandparents were longtime GOP delegates from Wisconsin and were deeply immersed in the Republican Party.

    Can anyone think of another president of the United States that so frequently made official pubic statements threatening, harassing and bullying American citizens who are literally trying to live through a disaster? In the middle of a disaster has another president said he was cutting off disaster relief? Has another president willfully spread lies and misinformation to American citizens during a disaster? What does it say about our country that we continue to allow this? What does it say about you if you condone and defend the words and actions of the current president of the United States?

    • Yes, indeed, someone in an authority position in the logging industry has to stand up to Trump, and tell him he is wrong, on many forestry issues. Trump’s ignorance is hurting our forests, and hurting the push for more active management. What is needed will cost lots and lots of money, and I’m not seeing any being freed up by the Republican Senate. Congress cannot even see the issues and problems, much less any real comprehensive solutions.


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