By: Andrew Avitt, Sept. 30, 2022-
Topography of a landscape affects fire behavior, like this steep terrain on the Plumas National Forest, traversed by the visiting Canadian Quebecois Fire Crew during the North Complex Fire in 2020. (USDA Forest Service photo by Kai Funk)
The Forest Service and its local, state and federal partners in fire suppression estimate that 98 percent of wildfires are suppressed before they grow larger than 100 acres. Wildland firefighters are exceptional at suppressing new starts, within the first 72 hours.
These are the wildfires that rarely make the headlines or are extinguished before media get a chance to cover them. The other two percent, the wildfires that are usually labeled extreme or catastrophic can sometimes take months to fully contain and may seem mysterious or to happen by chance.
In reality, wildfire behavior is very much a science, their causes and prevention strategies known.
Nic Elmquist, a Fire Behavior Analyst with California Incident Management Team 15, has spent 23 years working in and studying wildland fire. Fire behavior analysts like Elmquist understand fire on a personal and scientific level. They seek to understand its behavior and predict it, to inform firefighters operations on the ground and in the sky.
“We take the information that the environment is telling us—information from satellites, drones, research, online reports, and valuable knowledge from local communities—to predict how a wildfire is behaving and where it might be headed,” said Elmquist.
Elmquist outlined three main factors that influence wildfire behavior– topography, fuels and weather. “When certain levels of those three elements exist, that is when conditions are right for extreme wildfire behavior, the kind of fire that is typically hard to contain,” shared Elmquist.
Topography – Terrain-Driven Wildfire
Weather readings, like this one taken at Big Hill Lookout over Silver Creek Canyon during the 2014 King Fire, help inform fire modeling to better predict the patterns of future fires. USDA Forest Service photo. (USDA Forest Service photo)
Whether it is rolling hills, mountains, canyons, or flat meadows, the topography of a landscape affects fire behavior. Steep terrain is amongst the most notorious in the wildland firefighting community.
“Not only do fires run faster uphill but with steeper landscape, firefighters encounter what we call ‘rollout,’ hot material embers or logs, that roll downhill and then burn back up,” said Elmquist. “Steep canyons also tend to funnel the wind in different directions, and the wind is going to drive a lot of that fire behavior.”
What’s Fueling the Flames
The fuel for a fire is anything that is combustible. In the wildland environment it’s mostly vegetation, trees, and shrubs or organic materials on the ground called duff.
“On forested landscape, vegetation can be viewed as two types,” said Elmquist. “The live fuel like standing trees, shrubs and herbaceous material on the ground, and then the dead material, dead trees that have fallen over, pinecones, and other litter.”
Fire behavior analysts like Elmquist use samples of those fuels and the moisture levels inside to build models predicting fire behavior.
Abundance of fuel is one of the biggest influencers. Elmquist pointed out, “We’ve gotten really good at fire suppression over the last 100 years. We’ve suppressed a lot of fires, and one consequence is that those fuels have accumulated on the ground over the years.”
That buildup of fuel on the ground, coupled with overstocked forests with many dead, dying or stressed trees, means more fuel for a fire and much more intense wildfire behavior.
Weather and Fire Behavior
Tree thinning, like this on the Sierra National Forest, helps fuels reduction before and during fires to control fire behavior. (USDA Forest Service photo)
With an understanding of topography and fuels, fire behavior analysts work alongside incident meteorologists to determine how weather patterns will affect fire behavior.
Wind and temperature are some of the more influential factors when it comes to wildfire behavior.
Wind fans the flames by delivering a critical component – oxygen – to a fire and directing the fire’s spread. High winds cause flames to heat and eventually ignite vegetation in front of it and often carry embers to unburned areas, starting a spot fire. Extreme heat and sun will accelerate the drying of fuels, making them easier to ignite.
Another common weather event that makes some fires especially hard to suppress – lightning. Lightning can cause multiple fires across a landscape, stressing limited firefighting resources.
“In that scenario, we have to think about all of the fires together, which of the fires threaten life and property, which are readily accessible by road, and which terrain is safe for firefighters,” shared Elmquist. “These are all questions we consider in the aftermath of a lightning storm.”
In the case of lightning fires, firefighters also use fire modeling to see which fires have the highest potential for growth. Taking all that information into consideration, they devise a strategy.
“Partner firefighting resources from local fire departments, Tribes, state and federal agencies are critical especially for large fires that sometimes take months to contain,” said Elmquist. “And are also important to preventing and mitigating future large fires.”
Reduce Fuels, Reduce Extreme Wildfire Behavior
Of three main fire drivers Elmquist mentioned, two are uncontrollable – weather and the topography of a landscape. Reducing fuels becomes one of the main ways to mitigate extreme wildfire behavior and, in most cases, makes fires easier to suppress.
There are a variety of fuel treatments, each appropriate in specific conditions, such as prescribed burning, pile burning, and mechanical thinning.
“Any of these treatments remove a lot of those fuels, especially the dead fuels on the ground,” said Elmquist. “So when a fire occurs recently after a past prescribed fire or wildfire, it is going to have less fuel to consume and therefore it’s going to be less intense, easier to suppress.”
With less fuel on the ground and advanced fire modeling, wildfire firefighters use these tools to hit that 98% fire suppression rate. Ultimately, every preventive step along the way pays off exponentially each time a fire appears on the horizon.