A series of experts and panelists from the U.S. Forest Service and the University of Arizona’s Institute of Resilience recently held a webinar on Aug. 5, detailing their current assessments of the causes, damages and the prevention methods stemming from this summer’s Bighorn Wildfire.
Experts in the webinar were quick to remark on the damage this summer’s wildfire has had on the Tucson community, stopping thousands from enjoying hikes and being outdoors in the Catalina mountains for months, and forcing the local community of Summerhaven to temporarily evacuate.
“It was an emotional period too for those who were evacuated, and those who enjoyed hiking and such,” said Dr. Ben Wilder, director of the desert lab on Tumamoc Hill.
Several factors have been attributed to the cause of the fire and to why its fire spread so rapidly and burned extensively in the Catalinas. Panelists believe these causes are part of what makes the Bighorn Fire unique from other past wildfires in the Catalina range.
Lightning strikes on June 5 are the known cause of the fires. June this year experienced significantly low rainfall and high temperatures, causing a spell of dry weather that helped the fire’s spread.
“We had some pretty significant weather events that drove this fire,” said Jeremy Michael, a meteorologist from the National Weather Service, who was deployed to Tucson during the Bighorn Fire. “We had very hot, very dry and very windy weather in the coming months that fueled it, and in June we had several days with red flag warnings. It was the first time in Arizona a red flag warning issued in June since 1997.”
Red flags are used by the NWS as forecast signals for days where weather conditions are ideal for the spread and combustion of wildfires.
While the fire technically started on June 5, panelists largely attributed the weather conditions on June 17-19, days with high speed gusts of dry wind, to the fire’s massive and expansive spread.
“When wind is driving the fire, it turns into something different, it sweeps up trees and burns very intensely,” said Dr. Laura Marshall, a forest ecologist at UA. “What’s really noticeable is on these days with high winds most of the high temperature fires happened.”
Arizona researchers also emphasized how invasive vegetation species in the Catalinas, most notably buffalo grass, native to the plains in the African savannah, provided further fuel for spread of the Bighorn Fire.
“Buffalo grass is particularly worrisome, there are many invasive species, but not one that transforms the landscape like this,” said Dr. Kim Franklin, UA researcher and conservation director at the Arizona Sonora Desert Museum. “There’s not enough fuel in the natural desert landscape to sustain a fire … but one invasive grass, the buffalo grass can help contribute to the fire’s spread. “
Franklin believes buffalo grass is a perpetual threat to the Sonoran Desert, not only through damage in wildfires like the Bighorn, but also as a threat to other species of desert vegetation.
“Buffalo grass actually thrives on fires, where after a fire it’s going to grow back lusher than before … it exists in these discreet patches and these patches will continue to grow and coalesce to be an even bigger source of fuel in the future," Franklin said. "However, with or without fire, buffalo grass is transforming the desert as we know it, transforming a biodiverse desert landscape into a grassland.”
Several comparisons were drawn between the Bighorn Fire and the Aspen wildfires in the Catalinas from 2003.
“One really important difference between the Aspen fire and the Bighorn fire is the human toll,” said Dr. Molly Hunter, associate professor in the UA School of Natural Resources and the Environment. “At the end here, there were practically no structures were lost … and that’s different from the Aspen fire were tragically more structures were burned.”
Only two small structures owned by the U.S. Forest Service were reportedly burned during the Bighorn Fire, according to District Ranger CJ Woodard during the webinar, and no homes or businesses were damaged — unlike the Aspen fires of 2003 where nearly 340 structures, including several homes and businesses were burned down.
Despite the difference in human loss, the Bighorn Fire overall was larger and more destructive to the Catalina wilderness.
“When looking at past burn history the bighorn fire is noticeable because it’s one of the only fires to burn the whole range,” Marshall said during the webinar.
While the progression patterns of both fires were similar, starting from the southwest of the Catalina range and spreading to the north east, the Bighorn Fire was notably larger, burning 119,978 acres compared to 84,750 acres burned during the Aspen fires.
The scale of the Bighorn fire and the timing of the fires being spread during COVID-19 also led to a difference in the firefighting tactics used by the U.S. Forest Service. Wild land firefighters used the traditional combination of fire line construction tactics and air drops of fire-retardant spray to combat the Bighorn Fire, as well as utilized drones to survey fire damage, and slow burns to drop fire temperatures and protect lucrative species of vegetation, like the Saguaro Cactus and the Ponderosa Pine, according to Woodard during the webinar.
The Forest Service also had to combat the Bighorn also while maintaining and implementing public health measures to prevent the outbreak of COVID-19 amongst firefighters.
“The era of COVID changes the way we fight fire dramatically … we implemented a policy, so we could have firefighters contained in their own unit to stop the spread of the virus,” said Steven Miranda, a fire and safety staff officer with the Coronado National Forest.
According to Miranda, the cost of firefighting the Bighorn was around $44 million dollars, partly due to competition over resources during other wildfires in the southern Arizona region, meaning the deployment of Forest Service firefighters to Tucson from all over the west coast.
“We were competing for resources all over southern Arizona during the early June lighting storms,” Miranda said. “We were placing orders for firefighters and a lot of those fire fighters had to come from far away … it takes days for guys coming from Montana, Colorado or Idaho to come here.”
RELATED: Campus reentry update: Robbins announces longer reentry phases, says he "supports" employee union
With the monsoon season approaching in August, panelists also addressed concerns over erosion and flooding — with thousands of acres of soil now exposed due to the fires. Sludge or slurry flooding, water mixed with soil and charred wood, was problematic after the Aspen fires of 2003.
“The slurry is mostly a concern for aquatic systems,” Hunter said. “The main problem may be soil fertilizer that may cause algae blooms. However, we, and the Forest Service are working hard to make ensure that these impacts are minimal.”
Panelists also connected lack of precipitation and late timing of Arizona’s monsoons, largely caused by climate change, to the severity of the Bighorn Fire and the potential for more wildfires to occur in the near future.
All researchers and panelists concluded that the assessment of the Bighorn Fire is far from complete.
“It takes many months or even years to get an accurate assessment of what the fire actually did to the mountain,” Hunter said.
Follow Ian Tisdale on Twitter