Published: June 29, 2023 By ,

During an emotional press conference in early June, the Boulder County Sherriff’s office announced the findings of a lengthy investigation into the Dec. 30, 2021, Marshall Fire, the most destructive wildfire in Colorado history. They concluded that the mid-winter inferno, which destroyed more than 1,000 homes and killed two people, was likely sparked by smoldering embers from a pile of burning debris and a spark from an arcing powerline.

The findings do not surprise fire ecologist Jennifer Balch. Humans have evolved with fire, rely heavily on it, and, according to her research, are responsible for more than 97% of the ignitions that threaten homes and 84% of all wildfires. It doesn’t have to be that way, said Balch, associate professor of geography and fellow at the Cooperative Institute for Research in Environmental Sciences (CIRES) at the University of Colorado Boulder.

“I think we need a massive public messaging campaign around how our activities are contributing to these ignitions,” said Balch. “Smokey Bear was a hugely successful campaign for the woods. Now we need a Smokey Bear for the suburbs.”

CU Boulder Today spoke with Balch about what starts fires, how fire behavior is changing and what we can do to prevent them.

How would you characterize our relationship with fire?

People are the fire species. Fire is an integral part of who we are and how we live. We use it in our stoves, we use combustion to fuel our economy, we use it culturally. I would challenge anyone to think about living without fire for even just a day. So, it's not surprising to me that we also play a role in starting wildfires.

What role are people playing?

I like to think about three major ingredients to fire: ignitions, fuels, and a warm, hot, dry climate. People are changing all three. We provide the vast majority of ignitions—anything from debris burning to driving a car with a hot tailpipe off the side of the road to cigarettes to campfires to fireworks. July 4 is the single day of the year with the most human-started wildfires: There were 7,000 events over a roughly two-decade period. We’ve also been changing our landscapes in different ways that change the amount of fuel that's available to burn—over 20 years we studied, there were 59 million homes that were within a kilometer of a wildfire. And then the third piece is a hot, dry climate. The science is very clear that humans, through our fossil fuel combustion, have been contributing to warming the planet.

How are fires changing?

Since 2000, wildfires in the United States have gotten four times larger and three times as frequent. We’re also seeing more nighttime burning as a function of warming nights. We're seeing more extreme fire behavior. And we're seeing fires happening in the wintertime. For the first time in my career, I've talked a lot the last few years about snow putting out wildfires. That should really be an oxymoron.

According to Boulder County, the Marshall Fire was likely ignited by debris burning. How frequently does this happen?

Pretty frequently. In fact, 25% of over a million human-started wildfires we analyzed were started by debris burning. The next biggest category is arson, then heavy equipment, campfires, children and smokers.

What about power lines? Both the Marshall Fire and the Camp Fire in Paradise, California, are believed to have been ignited this way. (Xcel Energy in Colorado disputes this finding.)

With powerlines, it’s much more rare. But the challenge with powerlines is that when they do cause ignitions, it often happens during high wind conditions on hot dry days, so they can cause some of the worst, most devastating wildfires.

What can individuals do?

We need to be thinking about how our daily activities are contributing to ignitions, particularly during high wind conditions and very dry periods of the year. We need to be talking about how to reduce campfires and fireworks and not use lawn equipment that sparks. And we need to be thinking about what we are building our homes with, choosing materials like roof types and fencing that are not as flammable. Wood fencing can be a conduit for fire, essentially a wick to pull fire into neighborhoods. We can also reduce the fuel around our homes, creating fire breaks and removing flammable plants. Junipers, for example, have very high oil content, and they're extremely flammable.

What can society do?

Given that humans have such a deep and long-standing relationship with fire, it also means that we have the tools to live more sustainably with fire. That’s the hopeful message. There's a lot of undeveloped area that's going to be developed in the next 10 to 20 years. We need to consider where those homes are going and what they're going to be built out of. We have floodplain maps to help guide where we build but we don't have the equivalent fire maps. We also need high-level constraints, either carrots or sticks, to help us change where we're putting homes and flammable landscapes, particularly in the West.

Fourth of July is coming up. What should we keep in mind?

We have so many cultures in which fireworks are part of the celebration. It’s too bad our Independence Day didn't happen in the middle of winter. If you want to go to the city fireworks display, which is very controlled, and firefighters are making sure that it’s done in a safe way, that is probably OK. But individuals using fireworks is probably not a great idea.

It has been raining like crazy for the last month and a half in Colorado. What does that mean for our fire risk here?

It's good news in the short term and potentially bad news in the long term. It just depends on how hot and dry it gets this summer because we now have a ton of fuel in the landscape. I look at that green carpet on the mountains around us and I brace myself for when it's going to be hot and dry enough to burn.

CU Boulder Today regularly publishes Q&As with our faculty members weighing in on news topics through the lens of their scholarly expertise and research/creative work. The responses here reflect the knowledge and interpretations of the expert and should not be considered the university position on the issue. All publication content is subject to edits for clarity, brevity and university style guidelines.