A (Still Developing) Story of Three Fires

Like many fire scientists I know (or just people living in California), when a big fire starts happening in my area, I start obsessively following fire maps. My city is well-buffered, so fortunately I don’t have to watch evacuation maps too closely, but I keep tabs to stay up to date and to get a sense for patterns of fire activity in today’s world. I haven’t written anything here in a while, because I have other outlets for writing now in my job, but I made some maps and wanted to share them on Twitter eventually, and I wanted to add some context. So this won’t be totally polished, but I hope you find it interesting anyway.
I’m going to start with some background.
If you haven’t been following the most recent fire event in California, an unusual (but not unheard of) summer lightning event happened in mid-August, igniting fires mostly between 8/16-8/18 across the state of California. Most of the focus has been on three fires around the Bay Area, two of which quickly broke the top 10 largest fires list (the LNU complex, currently 391,150 acres & 72% contained, northeast of the Bay Area, and the SCU complex, currently 375,209 acres, 74% contained, east of San Jose), and one has made headlines for burning Big Basin State Park and approaching Santa Cruz (CZU complex, 85,378 acres, 45% contained).
Looking at your typical fire maps for an ongoing fire, there’s only so much to see: how big it is, where it is, how quickly it is burning and in what directions. But with some understanding of fire behavior and fire history, there’s other things to consider that aren’t visible on the map but that you might know if you are familiar with the area.
For me, the two big things I am interested in are: 1) what kind of vegetation is it burning in? And 2) what is the fire history there?
These are important parts of the map that are not visible on either the CalFire or SF Chronicle maps or most others you will look at, but they are really important. Vegetation and fire history give you insight into the big questions that everyone wants to know about–Is this normal? What is driving these fires? What should we do about it?
Contrary to what many news articles or even scientists may tell you, none of these questions are simple. Fire scientists have studied all of these questions, and there’s data that can help us answer each one. But none of them really can accurately be answered with a one-word or one-sentence answer, unless that sentence is “it’s complicated.” What does seem to be clear is that the answers to all of them depend a lot on vegetation type and regional fire history (see for example this paper or this one), so that’s a good place to start.
Okay, back to the fires currently burning in California: as I followed the maps, I was paying most attention to the LNU complex, because that is the closest to me and in an area I know well. And one thing I knew was that this area had seen a lot of fire very, very recently. Like multiple major fires in the last 5 years recently, and it seemed like a lot of that was reburning. If something is reburning in 5 years, or 2 years–that’s very noteworthy for an area with a lot of chaparral, which historically burned more like every 30-100 years. But without actually pulling the fire history maps together, it’s hard to say for sure how much was reburning. So I wanted to make that map.
The other reason to make that map was my growing frustration with rhetoric surrounding the fires that treated each of these three fires as having the same drivers and the same solutions. There are certainly commonalities, but a redwood forest is radically different from the shrublands and woodlands around Lake Berryessa. I wanted to make a picture that showed some of these differences. In 2018, I made a bunch of maps of the vegetation in several major fires that burned that year, and that was instructive. This time, I started with fire history, but I’m also working on new vegetation maps.
Okay, so for a fun Saturday morning activity, I started pulling fire perimeters into QGIS to get a better picture. I pulled in the perimeter data through 2019, and then the perimeters of the LNU, CZU, and SCU complexes. I also added in the prescribed fire dataset from FRAP. For the historical data, I created a new column to calculate time since the incident, so that I could then make the map colored by time since fire. Here are the resulting maps:
1) LNU Lightning Complex
Map showing perimeter of new fire overlaying a patchwork of fires in different colors. Much of the area inside has burned
As you can see, much of the LNU complex perimeter has burned very recently, maybe a third in the past 13 years (mostly in 2018 and 2015) and probably half in the last 30 years. The vegetation in this area is mostly a mix of chaparral and oak woodland. For oak woodlands, the historical interval would have been around 7-15 years or so, so this is on the higher end frequency-wise. For chaparral, though, which covers a lot of that red area, 30 years is on the low end or well under the historical fire interval, which is ~30-100+ years. So a lot of this area is not out of range at all, and if anything is primed for type conversion of chaparral to annual grassland from these recent fires.
There is a good chunk of the area that hasn’t burned on record or hasn’t burned in 50+ years. That’s not actually out of range historically–there would have been some areas like this, but perhaps that area would be even smaller without fire suppression.
What to take away from this? Well, this isn’t really a place where fire has been totally absent due to fire suppression. Much of it has more fire than it once did, not less, because of population growth and the ignitions that come with that. Is the fire it has now the same, behavior-wise, as the fire that it once had from cultural burning by indigenous people in this region? In some ways, but likely not in every way. Still, the story in this type of landscape is not purely about fire suppression, and severe fire in chaparral cannot be explained in that way. High-severity fire is typical for chaparral, and if there is any recent increase in intensity or severity, invasive grasses, changes in fire weather, and additional homes near wildland areas should be getting more attention than they are. Likewise, this is an area to consider the use of prescribed fire and fuel management very carefully–there may be a role for it, but we need to acknowledge that recent fire scars have not prevented these places from burning again.
Obviously, these are just perimeters and we don’t know what it actually looks like within–it’s possible some of these burn scars did burn less severely, but given the huge amount of reburn in the perimeter, these areas didn’t seem to stop the spread substantially, except maybe on the east coast of Berryessa, in part of the 2018 County Fire scar, and maybe in the southwest corner.
Okay, that’s enough for the LNU complex.
Let’s see the SCU complex.
The SCU complex also has a considerable amount of of area burned in the last 30 years (plus more prescribed fire than I would have expected), but not nearly as much as the LNU. I don’t know this area quite as well as the LNU area, but I think somewhat more is oak woodland. So while relatively recent fire did burn here, I’d buy that fire suppression has played a greater role here (which makes sense if it is indeed more oak woodland vs chaparral).
And the CZU complex:CZUHistoryWithRx.png
Well, one of these things is not like the others. Clearly a very different story there. There was one good sized fire there in 2009, and a small patch of prescribed fire (it looks like that’s up in the hills in Big Basin, but mostly this hasn’t burned at all. Redwoods historically burned quite frequently and this seems to fit the classic story of fire suppression. It will be interesting to see if the small area of prescribed burns moderated the severity at all.
Okay, that’s all I’ve got. I’m happy to hear other folks’ interpretations of what they see in these fire histories.
P.S. This blog post in no way whatsoever represents the opinions of the US Government in any way shape or form.

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