Was Colorado Marshall Fire an actual “urban firestorm”? No.

On December 30th fire whipped by 100 mph winds quickly burned through suburbs of Denver in Superior and Louisville. This is an area I drive through often, so I’m familiar with it and appalled at the rate of development in the last 25 years. It is right where Denver outskirts meet the Great Plains, but 5 to 8 miles from the Rocky Mountains. Is it urban or suburban?

approaching Superior, Colorado from Denver on route 36

Above is a Google Street View photo from the main freeway intersection in Superior. Below is a map with the fire area in red and a green dot showing the location of the photo.

Google Map of North Denver from I-70 through Boulder including Marshall fire area. The airport is about 25 miles to the east.  The Rocky Mountains run down the west edge of Boulder. Notice the relative steepness is greater to the west of Boulder, Superior and Louisville.

An interesting article by climate journalist David Wallace-Wells, who lives in the area, gives details and links in many videos, here https://nymag.com/intelligencer/2022/01/colorado-saw-the-return-of-the-urban-firestorm.html?utm_source=pocket-newtabc .

Wallace-Wells says the fire was scarier than a forest fire. No doubt so, as it was extremely swift and surprised people who don’t live in the forest. He calls the event an “urban firestorm”. But the area appears to me to be distinctly suburban, and on the edge of the suburbs next to prairie, and so more likely a suburban prairie fire.

Fires are an essential part of a prairie ecosystem. According to http://www.museum.state.il.us/muslink/prairie/htmls/eco_importance.html they do two things:

  1. slow down the invasion of trees from the edges of the prairie and from wind-blown seeds
  2. speed up decomposition to return nutrients to the soil

From the same link is the following description of a prairie fire:

“We stood in the doorway for a moment, transfixed by the column of fire towering in the black sky. It was a prairie fire–still far away but being blown toward our place by high winds, and coming closer all the time.”-from Brett Harvey’s My Prairie Year: Based on the Diary of Elenore Plaisted

The description matches closely the description of the Marshall Fire. We have just gotten very good at preventing prairie fires, or containing them with barriers like roads, but this fire may have started in a canyon (where crews were already working on a downed power line) and the wind was high enough to blow across barriers. The source of the winds according to the Denver Post was an “amplified mountain wave”. What is a mountain wave? It is like water flowing over boulders, and speeding down the other side of a boulder in a sudden, turbulent drop. . .

Notice the comment in the caption about drops exceeding 1000 meters. That’s around 3000 feet. Is there a drop that large there? I’ve often been impressed by the steepness of the near cliffs as one approaches Boulder on 36, but how high are they?

High enough. Notice the rise directly west of Boulder is rather gradual in comparison. But just south of Boulder, opposite Louisville (on the right), the red area in the 2300-meter range comes within two miles of the 1600-meter range of the Great Plains. That’s 700 meters, pretty much the better part of 1000, and very sudden. At Denver it becomes gradual again. In Denver and Boulder, mountain waves would be relatively less severe. There is a specific geographic risk in Superior and Louisville. And probably the other northern fringes of Denver. Development should stop there and probably retract. If you don’t think development can retract in response to weather events, come look at the former subdivisions near me in flood plains which are now completely devoid of houses. People are forced out by the Federal Government if their property floods a second time.

Look again at the road and topo map (the first one) at the marked fire area. It is directly across from the highest and most abrupt near-cliff edge of the Rockies.

The fact some trees had been allowed to invade this prairie just added kindling that produced the initial swarms of embers that invaded buildings burning them from the inside. Thereafter as the buildings combusted and added to the embers, they were the fuel that substituted for the tall grasses of a true prairie fire, as opposed to just a grass fire. But with no dense trees to keep the higher winds up from ground level, it was likely a new type of fire, a suburban prairie fire.

The area where I live, south of Houston, was once tall grass prairie, now invaded by homes and trees. The annual rainfall is much greater than on the Great Plains, but in a dry year we can have dangerous grass fires. Rarely there is a dry westerly wind. But most of our wind comes from thunderstorms or tropical storms and contains water. As one goes north and west conditions become drier and the wind picks up. By the time conditions become right for pushing a fast prairie fire, the prairie has given way to the near-desert of northwest Texas. Over grazing by cattle has eliminated prairie grasses and they are replaced by scrub brush. There is little to burn unless you can start a fire from electric windmills, which now sprout like giant white grass stalks.

To call it an “urban firestorm” is a bit of a scare tactic it seems to me.  Without the grassland, where would embers have come from?  Starting the fire in an actual urban area would have been considerably more difficult.  Typically, urban firestorms have either occurred where there were wooden city centers (generally over 100 years ago, e.g., San Francisco and Chicago fires) or as a result of war and firebombing (Dresden) or nuclear attack. Specifically, the source of wind in an urban firestorm is not external weather, but the fire itself.

From Wikipedia writeup on firestorms

Let us not get sloppy with language in the interest of scaring people into doing something that will not likely help the problem. A firestorm must have the wind dynamics shown above. Otherwise, it is a forest or prairie fire. Weather at the eastern foot of the Rockies has been violent since long before climate change. Just flying in and driving through the area makes me more nervous than driving winding mountain roads. Often thunderclouds and lightening are pervasive, with sudden wind gusts.

I suggest looking more closely at the geography of the area around Superior and Louisville. The foothills become more abrupt there, basically cliffs by the time you get to Boulder. Identifying specific areas where there is a dangerous wind dynamic in or near the Colorado mountain regions has long been a practice. How often do you see development in an area labeled as having dangerous wind gusts? Never in my experience. We should keep it that way, and not try to use every event to justify a memetic ideal of global hunkering.

To the extent humans cause climate change, the cause is too many humans. Controlled fire is a two-million-year-old invention, made by other hominids not even homo sapiens. You are going to give it up? Fine, then whatever technology you replace it with will have the same problem. Seven or ten billion people using it will obliterate the environment, whether it is mining rare earths in Mongolia. . .

Or cobalt in the Congo. . .

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