Learn how wildfires ignite and grow
- While flooding is currently a problem in many states, wildfire risks aren’t far behind.
- What causes wildfires? A heat source such as lightning, fuel (dead leaves, grass) and oxygen.
- Manmade causes: arson, unattended campfires, debris burning that is out of control, fireworks, discarded cigarettes and more.
This article was originally published on Zurich Insights. It is used with permission and updated to better fit the needs of Arrowhead’s producers and their clients.
All the rain that much of the U.S. has experienced this spring could very well lead to an increase in wildfire risks in the fall, when added vegetation dries to become fuel.
NASA data shows a steady rise in fires in the Western U.S. over the last six decades. While some unpredictable contributors, including lightning strikes and acts of arson, are major factors in wildfire occurrences, the scientific consensus is that climate change will continue to result in larger, more intense fires in regions prone to them.
So, in facing this volatile reality, businesses, communities and individuals need to plan early and intelligently for mitigation, response and recovery efforts. Before making those plans, however, a general understanding of the nature of wildfires and evolving conditions is helpful.
What causes wildfires?
There are three components required for a wildfire, often referred to as the “Fire Triangle”:
- Heat source: This can be anything from the sun to a bolt of lightning to a lit match.
- Fuel: This can be any flammable material, including dry, dead grass, leaves and trees and some forms of living vegetation.
- Oxygen: Fire feeds off oxygen, which increases in high winds, helping spread the fire.
Wildfires are a natural — and often essential — part of our ecosystem, but like destructive storms, their power can quickly overwhelm regions and their inhabitants. Moreover, while there are natural triggers for fires, human activity is estimated to be responsible for more than 85% of wildland fires in the U.S.
Human-caused wildfire triggers include:
- Campfires left unattended
- Intentional acts of arson
- Burning of debris
- Equipment use (including power lines) and malfunctions
- Discarded cigarettes
Related: Wildfire safety tips for businesses
Prescribed fires (or controlled burns), set intentionally for a number of beneficial reasons including reduction of more extreme wildfires, have also sometimes gotten out of control. While still considered an important strategy by many experts, with increasing heat and drier conditions, there is serious debate about when and where to employ controlled burns.
Whether natural or man-made, in terms of wildfire risks, the trigger is less important than the conditions for spread and intensity.
Conditions that increase wildfire risks
Our ecosystem is always in a state of delicate balance; several factors can adversely impact that harmony. In terms of wildfire risks, these include:
- Extreme heat
- Insects and disease that cause trees to die prematurely
- Bad land management
- High winds
Excessive heat, droughts, insects and disease have plagued human and animal life long before climate change was on anyone’s radar, but most of the conditions above have been impacted by or significantly contributed to the effects of climate change.
The historically warmer, drier conditions we are experiencing result in longer heat waves, increased drought, lower soil moisture content, the spread of damaging insects, and an increase in combustible fuels created by dead trees and plants all contribute to wildfire risks. Deforestation (mainly caused by logging) and poor land management have resulted in an increase in wildfires in regions where historically they were very rare.
It’s also important to note that wildfires can lead to increased risks for flooding, mudslides and debris flow. The destruction of trees and grasslands that could absorb rainfall can leave areas downhill and downstream more vulnerable to these events.
Types of wildfires
Three main categories of wildfire exist:
- Ground fires ignite within the soil, feeding off organic material like plant roots and smoldering until they grow into a surface or crown fire.
- Surface fires burn in dead or dry vegetation, such as parched grass or fallen leaves or branches at ground surface level.
- Crown fires burn through the top layer of foliage on a tree. They are the most intense type of these three and often difficult to control.
Wildfires can also be defined by regions and their associated climates. “Wildfire” has widely replaced “forest fire” as common terminology for wildland fires, but “forest fire” can be useful in distinguishing fires in woodlands from those in grasslands or shrublands, often called “brush fires.”
Where are wildfire risks growing?
Frequency is a major concern in some areas, but growing severity and duration can be equally troubling indicators in regions where the overall number of fires may actually be decreasing.
While fatalities are the most tragic immediate outcome of a fire, they are more an indicator of the success or lack thereof in responding to the fire than the level of risk. Small fires that are poorly managed or that ignite unexpectedly can be more lethal than fires of historic size or duration where evacuations of populated areas were effective.
Similarly, immediate man-made conditions can be hard to compare from a data standpoint to longstanding and evolving climate-driven conditions, whether driven by human activity or not.
However, it’s useful to look at regions that suffered from major, recent impacts of wildfires; the conditions that led to those fires; and what indicators may be for the future:
Over the last three years we’ve seen an increase in wildfire risks nationwide. Last year 66,255 fires burned more than 7.5 million acres. While the number of wildfires and acres burned were higher than the 10-year average, experts say the season could have been worse. Unexpected wet weather helped curb severe fire seasons in New Mexico and Alaska. In California, resource availability played a role, but so did weather conditions that consistently went in the state’s favor.
In 2021 we saw 58,733 fires that burned more than seven million acres. The Dixie Fire became the largest single wildfire in California history, burning nearly 1 million acres. The Dixie and Caldor fires also became the first known wildfires to ignite on the western slopes of the Sierra Nevada and burn over the rocky, high-altitude crest, and down the eastern side.
The 2020 wildfires wreaked havoc across California (which experienced six of the 20 largest fires in its history), Washington and Oregon. Expectations for more droughts and increasing landscape degradation mean the Western U.S. will continue to be at high risk for fires for the foreseeable future. Meanwhile, the Southwest U.S. is also expected to grapple with more high-severity fires that were less characteristic of the region in earlier periods.
What’s the cost of wildfires?
Between 2021-2022, wildfires accounted for over $11.2 billion in damage across the United States. 2020 wildfires in the U.S. caused $16.5 billion in damages, making it the third-costliest year on record; 2017 was the highest at $24 billion and 2018 a close second at $22 billion. These figures do not account for indirect damages, which experts estimate cost around $150 billion for the record-setting 2018 wildfire season.
What states have the most wildfire risks?
Bankrate says California is by far the most at-risk state for wildfires in the U.S., with nearly triple the number of properties at-risk in 2022 as the second-highest state. While #2 Texas had less than 717,000 at-risk properties, California had more than two million. Rounding out the top 10 are Colorado, Arizona, Idaho, Washington, Oklahoma, Oregon, Montana and Utah.
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