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How Do Wildfires Spread So Quickly?

Updated: May 9

On a recent weekend in mid-April, much of Northwest Oregon was issued a red flag warning by the National Weather Service, one of the earliest such warnings on record. The red flag warning means that critical fire weather conditions, including high winds, warm and dry weather, and low humidity, were occurring, or expected to occur. The warning included a statement to limit and closely monitor outdoor burns.

When the proper conditions align, wildfire can spread rapidly. A single spark from a cigarette, unwatched campfire, or faulted power line is enough to start a wildfire. Additionally, as the climate changes, wildfire season is starting earlier in the spring and extending through late autumn, especially in my home, the Pacific Northwest, and around the world.

What can be done to prevent wildfires? The American Red Cross offers a variety of tips for the general public to practice as wildfire prevention strategies. In addition, it is important that electric utility companies act ahead of time to prevent their lines from sparking wildfires. Prescient’s wildfire risk assessment can help.

Let’s explore the ideal conditions for the rapid spread of wildfire, as well as the speed at which a fire has the potential to spread. We’ll then look at some case studies of recent fires, and learn more about Prescient’s wildfire risk assessment tools for electric utilities.

Ideal Conditions for the Rapid Spread of Wildfire

A wet winter and spring, which lead to rapid growth of shrubs, trees, grasses, and undergrowth, create ideal conditions for the rapid development of wildfires once the dry season arrives. Following the rainy season, sustained hot and dry conditions throughout the summer often lead to drought, which dries out the growth from spring, creating ample fuel for fires.

Humans inadvertently start many wildfires by poorly tending campfires, discarding burning materials such as cigarettes, or lighting fireworks in dry areas with thick vegetation. Wildfires caused by faulted power lines are also of human origin. Natural fires, often caused by lightning, can occur as well.

High winds create ideal conditions to quickly spread wildfires. High winds feed oxygen to the flames, and help spread embers that travel up to several hundred feet in the air while remaining on fire. These embers spread beyond the reach of the flames, and can cause fires to start in areas not directly adjacent to the initial starting point of the fire. Wind-spread embers help wildfires jump to homes and developed areas, across cleared areas, and even across natural fire barriers like rivers.

Speed of Wildfire Spread

Wildfires spread rapidly through areas that provide a dense fuel source. They can move as fast as 6 miles per hour in forested areas, and 14 mph in grasslands. Wildfires often spread sideways away from the central starting point of the fire, creating a line of fire. This line can spread tangentially from the starting point, creating flanks of fire, which rapidly consume fuel as they are pushed onward by winds.

Wildfires can also spread in multiple directions from the starting point, depending on the direction and speed of the wind pushing the flames. Wildfires can shift direction quickly as winds change.

Wildfires are dangerous, but predictable. Conditions that can help wildfires spread rapidly are known; the unknown piece is exactly when and where the spark will occur. The Beachie Creek Fire, Camp Fire, and Eagle Creek Fire are recent examples of wildfires that spread from a small spark to a several thousand-acre blaze in a dangerously short amount of time.

Beachie Creek Fire, Oregon, 2020

The Beachie Creek Fire, also called the Santiam Fire, was a combination of over 15 small wildfires that started in August 2020, in central Oregon. Thirteen of the small fires were sparked by faulted power lines that fell or otherwise contacted vegetation during a record-breaking windstorm in September. The small fires merged to form a megafire, which burned over 400,000 acres in less than one month. Five people were killed by the fire; over 1,500 structures were destroyed across several small towns, including Detroit, Mill City, and Gates.

The power lines that started the fires were owned and operated by PacifiCorp. In March 2021, 100 victims of the fire filed a lawsuit against PacifiCorp seeking $1 billion in damages. As of March 2024, the case remained ongoing, with settlements expected to reach several billion dollars.

Camp Fire, Paradise, California, 2018

The Camp Fire began in the early morning hours of November 8, 2018, and burned for over two weeks. Northern California was amid a multi-year drought when a sparking power line, maintained by Pacific Gas and Electric, set fire to the forest. Within 4 hours of starting, the fire had burned through the town of Paradise; in the first two days, it burned over 100,000 acres. At the height of its speed, the Camp Fire burned the length of 80 football fields, which is about 4.5 miles, in one minute.

Thousands of people were evacuated as the Camp Fire raced through Paradise; 85 people were killed. The rapid speed at which the Camp Fire spread gave residents of Paradise little to no notice of evacuation. At least 18,800 structures, including 14,000 residences, were destroyed in the Camp Fire. Over 5,000 firefighters from multiple states were dispatched to respond to the fire; and 153,335 total acres were burned.

Insurance claims for losses totaled around $8.4 billion. Because PG&E power lines were identified as the cause of the Camp Fire, the utility company was on the hook for most of the cost of these damages.

Eagle Creek Fire, Oregon & Washington, 2017

By September of 2017, the Columbia River Gorge on the border of Oregon and Washington had not experienced rain in almost three months. Prior to this, a wet spring led to substantial growth of shrubs and undergrowth. Additionally, the Columbia River Gorge had not experienced a wildfire in several decades, which allowed years of plant growth and die-off to persist in the gorge, creating copious tinder for the flames. Conditions were more than ideal for a large and rapidly spreading wildfire.

The Eagle Creek Fire, which was started by a teenager throwing a firework into the drought-ridden forest, began on September 2, 2017 on the Oregon side of the Columbia River. By September 3, the Eagle Creek Fire covered 1,856 acres; on Sept. 4, it spread an additional 12,601 acres. On Sept. 5 alone, the fire spread across 15,426 acres. Within the first 72 hours, it covered a total of 29,885 acres.

On September 5, the Eagle Creek Fire spread to Washington state as embers carried by high winds jumped across the Columbia River, a seemingly natural barrier to the fire. It burned nearly 50,000 acres of forest on both the Oregon and Washington sides of the Columbia River Gorge. The fire burned from September 2, 2017 to November 30, 2017, with embers continuing to burn through May 2018.

Wildfire Risk Must Be Minimized

Wildfires are dangerous and difficult to quell. Dry conditions following wet growing seasons, high winds, and inattentiveness are the perfect combination to spark a deadly wildfire that can burn hundreds of thousands of acres in a single day. Wildfire season has begun to start much earlier in the spring, as was observed in Northwest Oregon this past weekend.

Prescient’s wildfire risk assessment service provides a comprehensive review and analysis of overhead power lines to determine their risk of igniting wildfires. After completing an assessment, we recommend prudent changes to power line construction, maintenance, and operation, as well as protective relaying schemes and design practices. Our recommendations will help electric utilities to modernize to the lowest possible wildfire risk.

Wildfires caused by faulted power lines are predictable and can be prevented. The conditions for rapid spread of wildfire, such as wind speed, relative humidity, and temperature, can easily be observed. Prescient’s wildfire risk algorithms accounts for these and other factors, including residual moisture and fault clearing time, which are more difficult to observe, but vital when predicting the likelihood of power lines igniting wildfires.

Wildfires can occur anywhere that conditions allow. Climate change and changing weather patterns are creating longer fire seasons around the world. Taking proactive steps before a wildfire occurs will prevent the forfeiture of human life and safety, the destruction of vital rangeland, cropland, and natural areas, and the potential loss of billions of dollars.

Learn More with Prescient’s Upcoming Webinar

To learn more about our wildfire risk assessment methodology, join us for our upcoming, free webinar Assess and Reduce the Risk of Power Lines Igniting Wildfires on June 6, 2024 at 10:00 a.m. PDT. Sign up today to guarantee your spot! Check out our wildfire blog series to learn more about Prescient’s innovative concepts for wildfire risk reduction, and contact us with questions.

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