The last few wildfire seasons have raised many questions in the minds of the general public and the property insurance profession. Why are so many acres burning? Why are so many homes and businesses at risk of damage or destruction? What can be done to reduce the risk and help prevent damage?
Research indicates the answers to these questions involve many factors, not just one or two. In this post, we explore the most significant factors and how they’ve evolved over the past several decades in the U.S.
Major influences affecting the frequency, intensity and destructiveness of wildfires include:
- Fire suppression policies that have led to a buildup of fuel in wildland areas.
- Increased development in areas prone to wildfires.
- Warmer, drier weather.
- Susceptibility of properties to wildfire.
Let’s take a look at these one at a time.
How does forest management affect wildfires?
Between 2011 and 2020, U.S. wildfires burned an average of 7.5 million acres of land per year, including federal, state, local and privately owned land. Last year, more than 10 million acres burned in wildfires.1 Though these numbers are large, they are not unprecedented. Between 1926 and 1943, more than 20 million total acres burned annually in wildfires throughout the U.S., and between 1944 and 1950, more than 10 million wildfire acres burned per year in the U.S.2
In the summer of 1910, wildfires burned approximately five million acres just on land managed by the U.S. Forest Service.3 On August 20, severe winds kicked up flames and spread embers in the Northern Rockies,4 causing three million acres to burn over the course of only two days.5 This event became known as the Big Blowup, and it cost 85 lives.6
To help prevent another Big Blowup, Forest Service leaders argued for continuing to pursue their goal of total fire suppression,7 which had been set in 1905 when the service was originally established.8 By 1935, the 10 a.m. policy was implemented, which called for every fire to be extinguished by 10 a.m. the day after it was reported.9 Policymakers and land managers wanted to protect natural resources,10 especially timber, a valuable product, and they didn’t yet understand fire’s role in forests.11
Prescribed fire, also known as controlled burning, helps clear underbrush that can fuel wildfires.
Preventing Fire With Fire
Fire has always had both benefits and costs. Although we don’t use fire as much in our everyday lives as our ancestors did, it has played a role in making everything from cooking to electricity to transportation and manufacturing possible. When uncontrolled, though, fire can cause devastation.
The same is true for wildfire, which can destroy homes, businesses and lives. However, fire can also be good for the land.
When forested land never burns, it becomes thick with trees. Some of these trees grow large and healthy and contain significant amounts of moisture, but some trees are small, weak and dry. In the absence of fire, underbrush — including grass, small plants, dried needles and leaves — also accumulates. The large, healthy trees have to compete with the small, unhealthy trees for water and soil nutrients, meaning they may lose moisture.12
If a fire ignites in this thick forest, the conditions are perfect for it to spread rapidly. The underbrush and small, dry trees serve as fuel, and the larger trees may be more likely to burn because they’re drier than normal. The fire can then climb to the top of the large trees and burn along the crown of the forest at the same time it burns along the ground. At this point, the fire becomes extremely difficult to fight.
In contrast, a forest cleared of underbrush and small, unhealthy trees has large trees containing more moisture. If a fire starts, there’s much less fuel along the ground, and there’s less chance the fire will crown.
Analysis of tree rings indicates that frequent, low-intensity fires were the norm in many forested areas in Washington state before fire suppression policies became widespread.13 These fires helped clear underbrush and maintain healthy forests.
Burned underbrush provides nutrients for the remaining trees, and fire kills pests that damage trees, including the bark beetle. In fact, some species of trees and plants actually need the intense heat from fire to reproduce.14
The policy of total fire suppression was introduced with good intentions, and over time, fire scientists learned more about the value of fire and the important role fire plays in maintaining healthy forests. By the early 1970s, the policy changed.15
However, while the policy was in place, decades of underbrush accumulated, and much of it remains. The two main ways to remove this underbrush are prescribed fire (also called controlled burning) and mechanical thinning. Prescribed fire involves setting fire to selected areas of underbrush and monitoring that fire closely to prevent it from spreading to large trees. Mechanical thinning can be used in place of or in conjunction with prescribed fire, and it involves pruning low branches, thinning dense forest areas and creating fuel breaks.16
These practices can help prevent severe wildfires, and one recent study from the University of Washington found that prescribed fire and mechanical thinning can help forests survive even severe wildfire damage.17 Prescribed fire is being implemented in some fire-prone areas in the state. For example, the Washington Department of Fish and Wildlife plans to treat 10,000 acres of land it manages by the end of this year.18
Although more effective forest management practices are being used on an increasing amount of land, it will take time for them to have a widespread impact. And, these practices are one important piece of reducing wildfire property risk, but they are not the only piece.
How does development affect wildfire risk?
Over the last several decades, as wildfire fuel accumulated in wildland areas, people moved to and built homes and businesses in what’s called the Wildland-Urban Interface (WUI). In general terms, the WUI is where wildland and development meet. There are specific, technical definitions of the WUI, but they’re not necessary to understand this aspect of wildfire risk.
When it comes to understanding the WUI, the most important thing is that it occurs when structures are in close proximity to vegetation without sufficient space around the structures.19 Many wildland areas in or near the WUI have decades of accumulated underbrush, making them prone to severe wildfire.
Examples include small towns in the mountains and exurban communities surrounded by wildland. The WUI is widespread, making up about 10% of the land area in the continental U.S. To see the WUI near you, check out this map from the U.S. Forest Service; areas in yellow and orange are in the WUI.
The WUI is also growing quickly. Between 1990 and 2010 (the latest year data is available for), the number of houses in the WUI grew by 41%, and the amount of land in the WUI grew by 33%.20
More structures in the WUI means there are more homes and businesses at risk if a wildfire does start, and more people in the WUI means wildfires are more likely to start. Research shows that human activity is the most common cause of wildfires and that almost every wildfire that threatens homes is started by humans.21
Below is just one example of development in the WUI, in a part of Chelan County, Washington. A similar pattern is playing out in many areas across the U.S.
This area in Chelan County is in the WUI. Seen here in 1990, there's a mix of buildings and undeveloped land.
Map data: Google
The same area in Chelan County in 1998. Many of the previously undeveloped lots now have buildings on them.
Map data: Google
The same area seen in 2017. More structures have been built and are now at risk if a wildfire starts.
Map data: Google
How does climate affect wildfire risk?
One fire scientist from Stanford University used a baseball analogy to describe to National Geographic how a warmer, drier climate increases wildfire risk. Imagine two runners are on base, and the batter hits a home run. The home run caused the runners to score, but the fact that the runners were already on base made it a three-run rather than a solo home run. Climate change is the equivalent of putting people on base.22
In other words, climate change creates conditions that make fires more likely to burn intensely. Researchers at NASA analyzed satellite data collected over two decades combined with forestry data to identify key ways this happens.23
- Warmer, drier weather makes accumulated fuels more prone to burn, and if they do ignite, wildfire can spread rapidly and become uncontrollable.
- Warmer weather makes lightning storms more likely, which can spark more wildfires.
- Higher temperatures at night don’t slow wildfire spread as well as cooler nighttime temperatures. As a result, wildfires can continue over longer periods and burn more acres.
Other research has looked at climate trends in specific areas. For example, new research indicates rainy weather now arrives in California about a month later than it did 60 years ago, leaving the state more vulnerable to drier fall conditions.24
Researchers at Oregon State University found that about one third of snow packs in Western states show significant declines since 1955 and that lower snowpack levels can lead to drought.25
These trends, and others like them, mean that when a fire starts, either due to human activity or lightning strikes, it’s more likely to find drier fuels.
What can a property owner do to reduce the risk of wildfire damage?
The causes of increased wildfire-related property damage that we’ve covered so far can’t be addressed by any individual person or community. But if your customers own a home or business in a wildfire-prone area, there are steps they can do to reduce the risk of wildfire damage to their property, and it’s something they can start today.
Reducing the risk of wildfire damage starts with the area around the home or business. According to the National Fire Protection Association (NFPA), small flames and embers are the primary ways wildfires spread to buildings. Embers, also known as fire brands, can travel up to a mile and can start spot fires, so keeping them out of buildings is an important risk-reduction measure.26
Individual and community efforts can help prevent severe property damage from wildfires.
The NFPA has developed resources to help you remove or reduce the combustibles around a building so that small flames and embers have fewer opportunities to turn into fires. This process is often referred to as creating defensible space. To understand how it works, think of the area around your home or business as three zones:
- The Immediate Zone, the area within five feet of a structure’s furthest attached exterior point. Keep anything combustible out of this zone, including firewood, propane tanks, furniture, flammable plants, landscaping bark and needles in gutters.
- The Intermediate Zone, the area from five to 30 feet from the furthest attached exterior point. Landscaping in this area should be designed and maintained to prevent fire from spreading.
- The Extended Zone, the area from 30 feet to 200 feet. Safe landscaping choices in this area help interrupt fire’s path and keep any flames that do occur small and on the ground.
Once the property owner addresses these three zones, the next step is to reduce the combustibility of the building. Combustible building materials can be replaced with noncombustible or ignition-resistant materials. Vents to attics or foundations and windows can be protected from ember intrusion. Measures like these are often referred to as home hardening, and recent research shows they’re effective.
A study of the damage done by the 2018 Camp Fire found that homes built after 2008, when California implemented new building codes that required homes to be hardened against wildfire, were much less likely to be damaged or destroyed than homes built under the previous, less stringent building codes. Read more in our blog post on home hardening. Learn more about ignition-resistant and non-combustible building materials in a guide produced by the Insurance Institute for Business and Home Safety (IBHS).
Reducing wildfire property risk is not a once-and-done project: a home or business and the surrounding space require regular maintenance. And, they require community effort. Protecting your individual home or business is a good start, but the benefits are limited if owners of nearby properties don’t take similar steps.
Imagine a neighborhood with many homes built close together. In many cases, one home’s Intermediate Zone overlaps with another’s. Homeowners must work with each other to create and maintain their zones. To help communities work together to reduce wildfire property risk, the NFPA holds a national Wildfire Community Preparedness Day and provides resources to help make the day as effective as possible. The NFPA's Firewise USA program helps communities work together to prevent wildfire-related property damage.
To help you better understand the risk of wildfire-related property damage in your book of business, we’ve developed the Wildfire Risk Tool, which gives you detailed information on any property in Washington state. Through our subsidiary, BuildingMetrix, we now also offer data for the contiguous U.S.
 Congressional Research Service, https://fas.org/sgp/crs/misc/IF10244.pdf
 World Fire: The Culture of Fire on Earth by Stephen J. Pyne, page 194
 World Fire: The Culture of Fire on Earth by Stephen J. Pyne, page 186
 World Fire: The Culture of Fire on Earth by Stephen J. Pyne, page 187
 CAL FIRE, https://www.fire.ca.gov/media/5425/benifitsoffire.pdf
 Washington Prescribed Fire Council, http://waprescribedfire.org/
 CAL FIRE, https://www.fire.ca.gov/media/5425/benifitsoffire.pdf
 U.S. Forest Service, https://www.fs.usda.gov/managing-land/fire/mechanical-treatment
 Washington Department of Fish and Wildlife, https://wdfw.wa.gov/news/wdfw-plans-controlled-burns-eastern-washington-wildlife-areas
 National Park Service, https://www.nps.gov/articles/wildland-urban-interface.htm
 U.S. Forest Service, https://www.nrs.fs.fed.us/pubs/55817
 National Geographic, https://www.nationalgeographic.com/science/2020/09/climate-change-increases-risk-fires-western-us/#close
 npj Climate and Atmospheric Science, https://oregonstate.app.box.com/s/5o4ionvk0ryivrcdoxun31hufwos87s3