6 wildfire terms to understand, from red flag warning to 100% containment
David Godwin, Director of the Southern Fire Exchange, University of Florida
Wildfires fueled by dry, windy conditions have destroyed dozens of homes in Texas and threatened hundreds of others there and in Oklahoma and Florida this March. They’re a sharp reminder to be prepared for what forecasters warn is likely to be a risky spring for wildfires, particularly in the southern Plains and Southwest.
I’m a fire ecologist and director of the Southern Fire Exchange for the University of Florida. Here are six terms you’ll often hear when people talk about wildfires that are useful to understand, both for preparing for fire season and gauging the risk when fires start.
Imagine looking down at a wildfire from an airplane. Firefighters want to build a perimeter around that fire with control lines, or firebreaks — areas cleared of vegetation — that they hope will prevent the fire from spreading.
Having 100% containment doesn’t mean the fire is out. It just means the fire agency has containment lines around it. There can still be burning, smoldering and active flames. When conditions are hot, dry and windy, embers can blow across the fire lines and cause spotting — fires started by those blowing embers.
In the end, it’s Mother Nature that typically puts large fires out for good, and it may be weeks or months before they are officially declared out.
Red flag warning
A red flag warning means weather conditions are expected that would raise the risk of dangerous wildfires spreading.
You’ll hear the phrase red flag warning used across the country, but the criteria actually vary by geographic location. For north Florida, for example, a red flag warning is triggered when relative humidity is at or below 28%, winds are 15 miles per hour or above, and the fire has met a threshold in the Forest Service’s risk calculations known as energy release component, or ERC.
The Weather Channel explains how wildfire risk is increasing.
Fuel refers to all the vegetative material that’s available to burn. It can be everything from leaves, twigs, grasses and sticks to bushes and shrubs and heavy logs on the ground.
It can be dead fuel or live fuel. The threat posed by live fuels also varies by region. In the Western U.S., grasses are typically available to burn only once they go dormant and dry out. In the Southeast, however, live fuels like palmetto and grasses will still burn quite readily because of their volatile oils.
During a wildfire, you’ll hear fire managers and firefighters talking about “burnouts” or “backfires.” Those are fires that are intentionally lit and allowed to spread toward the wildfire.
By burning off vegetation ahead of the wildfire, firefighters leave the wildfire with less fuel to burn in hopes of either stopping it or reducing its intensity.
Prescribed fires are similar to backfires, but they’re used well before a wildfire can start. Prescribed fires are intentionally lit under conditions considered safe, such as when winds are low and it’s not too dry. Like backfires, they are used to clear away excess fuel.
A prescribed burn has a prescription — a written plan that specifies the ranges of weather conditions that fire managers anticipate will be acceptable for using and then extinguishing the fires, as well as the resources needed to accomplish it successfully and the intended outcomes and objectives of the burn. In some areas, it can take years to write a plan and execute it.
The U.S. Forest Service shows how prescribed burns work.
Prescribed burns have additional benefits. They allow forest managers to reduce fuels in a way that can also promote good wildlife habitats and healthy ecosystems. Prescribed fires apply the positive aspects of fire in the safest way possible.
The term “complex” when talking about wildfires is purely about management. When you have a number of fires in a geographic area, instead of having an incident management team at each fire, for simplicity they’ll call it a complex and have one incident management team responsible for all of it.
In the Florida Panhandle fires in March 2022, for example, three fires were burning in a relatively close area, but the same fire teams were involved, so they opted to manage it as a complex. Similarly, a group of Texas fires later that month were named the Eastland Complex.
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David R. Godwin works for the University of Florida Institute for Food and Agricultural Sciences School of Forest, Fisheries, and Geomatic Sciences. He receives funding from the US Joint Fire Science Program in agreement with the USDA Forest Service Southern Research Station and the USDA National Institute of Food and Agriculture. He is affiliated with the North Florida Prescribed Fire Council and the Southeast Regional Working Group of the National Cohesive Wildland Fire Management Strategy.
This article is republished from The Conversation under a Creative Commons license.
KYLE GRILLOT/AFP via Getty Images
A series of lightning storms in mid-August 2020 hit Northern California, a region already experiencing a severe drought season, igniting what would become the August Complex fire. Over the course of almost three months, it burned through national forests, destroying 935 buildings and forcing the evacuation of thousands of people. By the time it was fully contained, its total range was over twice the size of California’s previous record and among the largest fires in U.S. history.
Less than a year later, the August Complex’s record was nearly broken when the Dixie fires broke out in Northern California, burning more than 963,000 acres and destroying more than 1,300 structures in the region.
New breakouts of megafires (fires burning in excess of 100,000 acres) have become a seasonal repetition in the Western United States. Wildfires are innate to forest ecosystems, clearing out dead debris and paving the way for new growth, but climate change has elongated dry seasons, increased temperatures, and widened the potential for large-scale wildfires. Beyond weather-related factors, the prevalence of insects like bark beetles damage trees and make them more prone to burning. Invasive vegetation such as cheatgrass also easily burns and contributes to spread.
Trees, traditionally a storage vessel for carbon, release carbon immediately when burning and during decomposition. The EU’s Copernicus Atmosphere Monitoring Service estimated that global wildfires in 2021 released 1,760 megatonnes of carbon emissions, just over what the nation of Russia emitted in 2020. Black carbon, or soot, can also travel beyond wildfire zones, absorbing sunlight and warming the earth further.
Beyond the environmental threats, the widening reach of wildfires threatens the displacement of countless residents. The Marshall fire in January of this year destroyed more than 1,000 homes in Colorado, demonstrating the harm a wildfire can cause in a densely populated area such as the suburbs. The Camp Fire in 2018 permanently displaced an estimated 20,000 residents in California’s Butte County. Despite this, people continue moving to wildfire-prone areas, putting a growing population at risk of longer fire seasons and associated health risks.
Throughout the mid-20th century, forest management largely focused on preventing forest fires of all scales. Smokey the Bear was a national mascot for fire prevention, overseeing a multi-decade decrease in the number and average size of fires. But without regular fires, debris built up. This, combined with other environmental factors, eventually fueled costlier, large-scale blazes that have come to define the current wildfire season.
Despite having nearly 10,000 fewer fires per year on average from 2011-2021 compared to 1983-2010, the average acreage burned by those fires per year has more than doubled. From 1983-2010, the average number of acres burned per year was about 4.4 million. That number has jumped to 7.5 million acres per year for the 2011-2021 time period.
Emma Rubin / Stacker
The total acres burned by wildfires in December 2020 was three times greater than the 10-year average for the month. The following year also experienced a damaging December, with a less extensive but still above average spread covering 336,984 acres. Wildfire season traditionally lasts May through October, but shorter winters and earlier snow melts have extended wildfire risk. 2021 set a record for days at preparedness level 5, the highest alert for wildfire risk.
The USDA Forest Service warned in 2021, “For years, agencies relied on seasonal firefighters for summer months, but now that wildfires are burning into the winter, they need to reevaluate their hiring plans.”
Emilia Ruzicka / Stacker
With the increasing severity of wildfires every year, it follows that more resources are required to tame the blazes. In 1999, just before the turn of the century, the Forest Service and all other Department of the Interior agencies spent a combined $515.5 million on wildfire suppression. During the course of the last decade, the average cost of wildfire suppression has skyrocketed to nearly $2.1 billion annually. The Forest Service carries the brunt of this cost, contributing approximately three-quarters of the funds each year.
Though there is not currently an official tracking mechanism for the cost of wildfire damages, academics across the country have attempted to estimate the economic impact of wildfires. In 2020, a team of researchers estimated that the 2018 California wildfires caused $148.5 billion in economic damages.
Emma Rubin / Stacker
At the national level, 89% of wildfires were caused by humans in 2021, but human-caused wildfires contributed only to 42% of total acreage burned. In the Southern and Eastern U.S., human-caused fires still cause the most damage, but elongated dry seasons in the West have intensified the impact of lightning when it does strike.
Dry lightning is created through high-altitude thunderstorms. Extreme heat and drought can cause rain to evaporate before it reaches the ground. Lightning fires can also pose greater damage because it can take longer for them to be detected, whereas human-caused fires are often closer to towns and high-traffic areas. Winds associated with dry thunderstorms can further fan the flames as well. These factors mean that even as the West is less prone to lightning than other parts of the country, the bolts can spark more damage.
Emma Rubin / Stacker
While lightning has sparked some of the most devastating fires in California including the August, SCU, and LNU complex fires, powerlines have also fueled far-reaching damage. Contact with overgrown trees, downed lines, and frayed wires can spark flames. Pacific Gas & Electric was held responsible for the 2018 Camp Fire and 2019 Kincade Fire and has instituted rolling blackouts on high-risk wildfire days.
Even as the origin of fires varies, each is exacerbated by existing environmental factors. A 2018 survey from the USDA Forest Service identified nearly 150 million trees that died between 2010-2018 in California. Two years later, 2020’s record season burned nearly 4.4 million acres and the five largest megafires happened concurrently in August and September. The season demonstrated how the buildup of vulnerable trees can ignite unprecedented spread.
A 2021 aerial survey by the USDA Forest Service offered some hope. Annual tree mortality has declined over the past five years, with an estimated 9.5 million dead trees in the state spanning more than 1 million acres, although tree mortality remains at a much higher rate than California’s pre-drought levels in the early-2000s.