Do wildfire seasons still exist? What we know about Arizona's new year-round fire season
Across the West, fires are burning for 100 more days than they used to five decades ago. Conditions that would seldom allow a fire to spread now do, and most fire managers and researchers resist saying there is a wildfire season in Arizona.
“There used to be one,” said Donald Falk, a researcher at the University of Arizona who specializes in fire history and ecology, ecosystem resilience and restoration.
“Now it's approaching a 12-month fire season.”
Wildfires in Arizona were once expected from late April into the monsoon season. Now fires can start from late February or early March into September, Falk said.
The U.S. Forest Service and many other agencies are shifting to the concept of “fire years.”
“We really don't say we have a ‘fire season’ because we can have activity throughout the state year-round,” said Tiffany Davila, spokesperson for Arizona’s Department of Forestry and Fire Management.
“We can see fire activity increase during the end of April, beginning of May.”
Larger incidents, more erratic and aggressive fires, tend to peak when there’s a combination of hot air and windy conditions, and ease when Arizona is well into the monsoon.
Fires start earlier in southern Arizona and later in the north; each ecosystem has its own, unique relation to fires.
In ponderosa pine ecosystems, low-intensity fires historically moved across the landscape through large portions of the year, said Rogers Trueheart Brown, deputy fire staff for the Coconino National Forest. That ecosystem “evolved with fire” because of frequent lightning events.
Three main factors affect fire seasonality:
Decades of fire suppression — not letting forests burn naturally — cause timber, grass and brush to accumulate and cause more intense fires.
Where most fires were once started by lightning, they are now largely started by people. More humans in wild places mean both more chances of fire and higher stakes while fighting them.
Multiyear droughts and more extreme weather events due to climate change are driving longer, more damaging fires.
“We talk fire all year round,” Brown said. “Up in Flagstaff, we've had a banner snow year, but we're still talking fire come the beginning of January, just before Christmas.”
It wasn’t always this way, but, Brown said, “we’re learning to live with that.”
The four experts interviewed by The Arizona Republic said the biggest challenge of a fire year instead of a fire season is helping the public understand and act accordingly.
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How are fire years forecast?
Monitoring is a collective effort, as almost everything is when it comes to wildland fires.
The National Interagency Coordination Center, a national support center for prevention and response, publishes seasonal and monthly outlooks for fires across the U.S.
These predictions provide a good starting point for managers on the ground, who then refine the outlook from a regional to a state perspective to a forest perspective to a district perspective.
“Everybody does it a little bit differently based on what historically they've seen on current conditions and outlooks,” Brown said.
Discussions on preparedness and fire danger occur weekly. These conversations, among national forests in Arizona and New Mexico, are constant throughout the year, Brown said. It helps them “calibrate what’s going on” and move staff and resources around to respond to fires.
How do Arizona fire managers forecast fire danger?
Most agencies also have their own fire behavior analysts on staff. Arizona’s Department of Forestry and Fire Management works with both the National Interagency Coordination Center and the Southwest Coordination Center to predict “wildfire potential.”
The model used for these outlooks is the ERC, short for Energy Release Component, is an index calculated using multiple variables to predict the potential for a spreading fire. The index is low in winter and increases as fire builds up, as weather changes over the seasons. In the Southwest, it generally reaches its yearly peak in May and June, Falk said.
The vapor pressure deficit, a measure of how much water plants evaporate versus how much they can take up, has also become useful in predicting and monitoring wildfires. Although it’s well researched, its application in Arizona is still incipient, said Andrea Thode, professor of fire ecology and fire science at Northern Arizona University.
Thode and other researchers used that data and wind data to create charts for Grand Canyon National Park that allow managers to understand how the weather in the upcoming days relates to burn severity and large-fire progression. The tool uses data from past fire incidents and weather to help managers think about what might happen with a current fire and when there might be results they don’t want.
The hope is that these emerging tools used by fire scientists can give land managers and crews better information to deal with the changing fire landscape. That cannot happen if both parties are not at the same table. The pressing questions need to come from folks on the ground.
There has not always been close collaboration on research, but there's a lot of work to change that in Arizona, said Thode, who used to work for the Forest Service and is now the principal investigator of the Southwest Fire Science Consortium.
"The ultimate goal is working hand in hand from the start to the finish of our research to be able to make sure that what we're creating is applicable and digestible," she said.
What is the fire behavior triangle?
A fire needs two things: an ignition process and the conditions for it to spread. The conditions, Falk said, can be further boiled down to three things: weather, fuels and topography.
Weather includes a lengthy list of variables, such as air temperature, humidity, rainfall, wind speed and wind direction.
Fuels, in fire lingo, refer to the grasses and brush in desert lands and the timber and bushes of higher elevations. What kind and how much of it there is in a region, and where it exactly is — next to a town, inside a canyon, within a large forest patch — changes the fire outlook.
Each type of vegetation holds different amounts of moisture and can be more or less fire-prone.
"The fuel type in southern Arizona is mostly grass and brush, which is also called a fine fuel. So they don't hold a lot of moisture to begin with," Davila said. "Once we heat up, that fuel type dries out and now we have basically kindling across southern Arizona."
Some fuels, like grasses, change a lot throughout the year. Very wet winters can lead to very big fires.
Invasive vegetation like buffel grass, which thrives under frequent fires, has also increased the spread and frequency of fires in many regions.
“It's a simple equation. More fuels equal greater, bigger fires,” Brown, deputy fire staff at Coconino National Forest said. Fire crews in the district keep up with vegetation growth by thinning forest patches, creating clear-outs and doing pile burns.
Topography is the only factor that does not change. However, it does influence how fast fires spread, and thus their severity. Vegetation changes with elevation, and the orientation of a slope can mean that some areas receive more or less moisture, or more direct sun, for example.
Changes in these conditions have made wildfires much more variable. Erratic, dramatic weather events linked to climate change create conditions that increase the vulnerability of many ecosystems. Higher winds, higher temperatures and less moisture make the same fuels burn easier.
When wet winters, which increase vegetation growth, are followed by extended droughts, intense fires are more likely.
There is a fourth important factor: humans increasingly moving into areas that didn’t have humans before. This change, on what's called the wildland-urban interface, is one of the big drivers of out-of-season fires and complicates preparedness and firefighting.
Thode said this challenge is particularly big in Arizona, where the wildland-urban interface makes up "quite a big percentage of the state."
This close proximity also means even small fires can carry large consequences.
"An incident could be a five-acre fire, but that means that five-acre fire is threatening structures, it's calling for evacuations, it's shutting down major highways," Davila said.
How can Arizonans live with fire?
Arizona and many regions throughout the country have historically relied on a large seasonal workforce to fight wildfires. With fires becoming a year-round threat, more districts are increasing permanent staff positions.
Brown says northern Arizona has gone from 15% to about 33% permanent workforce in the time he's worked there. The crews are also working a significant amount of overtime.
“There have been incremental changes over about 20 years or so. But I would say the majority of the changes have come in the last four years,” he said.
"We are learning to live with fire."
Residents need to be aware that, even under unsuspected conditions, fires are more likely to happen. And humans are now the leading cause.
Brown is worried that the historically wet winter will make people dismiss this.
"In 2010 with a very similar snowpack, we had the Shultz Fire up here in northern Arizona. Once those winds kicked in, which we typically get here this time of year, it dried out the fuels very quickly and we still had a pretty devastating fire," Brown said.
Thode said one of the research frontiers for scientists working closely with land managers has been the public perception of wildfires and finding more effective ways to foster fire preparedness and awareness.
Her forecast for the aftermath of the snowy winter is similar: People might not realize they're in fire season, but it's started.
"This is the time to be thinking about what work you can do around your house," Thode said. "Do they have a plan for if they do have to get evacuated? All of those things. This is the time to think about that."
Clara Migoya covers environment issues for The Arizona Republic and azcentral. Send tips or questions to clara.migoya@arizonarepublic.com.
Environmental coverage on azcentral.com and in The Arizona Republic is supported by a grant from the Nina Mason Pulliam Charitable Trust. Follow The Republic environmental reporting team at environment.azcentral.com and @azcenvironment on Facebook, Twitter and Instagram.
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This article originally appeared on Arizona Republic: When is Arizona's wildfire season and how has it changed over time?
