Wildfire Knowledge Hub

Wildfires present a significant--and growing--threat to life, property, and increasingly insurer balance sheets across the US. However, historically wildfires were often overlooked as a significant peril for P&C insurers. For decades, wildfires were not a significant driver of losses, especially when compared to the much more visible losses from hurricanes, severe convective storms, and flooding. In the nearly 20 years from 2000 to 2018, combined wildfires losses only ranked 7th in the world in terms of insured catastrophic losses, but most of those losses come from the US (Insurance Information Institute (III) Fact Book 2020).

The wildfire seasons of 2017 and 2018 marked a dramatic change that put wildfires firmly back in the public conscience and put a significant dent in insurer's balance sheets, especially in California. After a welcomed reprieve in 2019, the 2020 wildfire season—the " Fire Siege " as it was dubbed—was equally unprecedented. Where wildfire losses were once easy to overlook, they are now front and center. This Risk Awareness Service from AAIS will provide a curated look at the wildfire peril, what you need to know, what you and your policyholders can do to reduce wildfire losses, and other actionable information to address the wildfire peril.

Wildfires are a natural part of forest ecology and the natural environment. Wildfires have been present as long as there has been forests. While perhaps counterintuitive, wildfires serve an important role in the health of forests and rangeland. Many landscapes across the US are considered fire-adapted or fire-dependent ecosystems where the native flora and fauna have adapted to survive wildfires and often rely upon wildfires to remove competing invasive species, to open seed pods, and to speed regeneration of the forest.

Not only has the natural environment adapted to wildfires, so too did early indigenous people adapt to and learn to utilize wildfires. Indigenous people used fire to prepare farmland for crops, to drive animals for hunting, and to remove brush. In many ways there is little new or novel with wildfires in the US. Wildfires are a normal and natural part of the landscape of our country.

What has changed is how we have dealt with wildfires in modern society. The role wildfire plays in our forests and in our lives has changed with the significant expansion of homes and communities in wildfire prone areas and this all increased the threat that wildfires pose to homes and businesses. The  III  notes that upwards of 4.5 million properties, nearly half of which are in California, are at extreme risk of wildfires.

We have learned a tremendous amount about wildfires in the past century and that knowledge continues to increase with each passing year. In the following sections we will outline the latest knowledge in the following areas:

• Latest understanding about  wildfire science ,  fire ecology , and how  wildfires behave ;
• Common  wildfire causes  and how investigators determine the causes of wildfires;
• How  buildings burn  during wildfires and how to build more resilient homes that can resist most wildfire ignitions;
• How wildfires are  suppressed  and the varying approaches and resources used to fight wildfires;
• Wildfire  mitigation  efforts by  property owners ,  neighborhoods , and local governments.

NOTE: For the purposes of this document we will primarily refer to all types of outdoor vegetation fires as wildfires. There are several regional and colloquial terms for wildfires, including forest fires, brush fires, grass fires, wildland fires, bushfires (primarily used in Australia and New Zealand), veldfires (primarily used in South Africa), and many more. There can be important distinctions (i.e. forest fires vs. grass fires) but by in-large these refer to the same phenomena.

To see where wildfires are currently burning the National Fire Situational Awareness map was made available by the National Wildfire Coordinating Group (NWCG) — a consortium of federal agencies with wildfire responsibilities. This map consolidates large amounts of data for wildfire policy leaders and decision makers. This includes satellite remote sensing data from  MODIS  and  LandSat  that shows active heat signatures that show not only the location of wildfires, but can be used to infer the direction they are burning. NWCG also include information on the official status and containment estimates from incident commanders on the ground.

You can also review a list of active wildfires including information on the current acreage, personnel assigned, and other relevant layers in the new ESRI Wildfire Aware application:

This tool includes data from a host of sources like  InciWeb  or the  Wildland Fire Locations  dataset. These may exclude some wildfires being handled by local fire departments. (We will discuss the different and overlapping jurisdictions in the section  Wildfire Suppression .)

A common observation is that wildfires and heat signatures are visible across the entire country. Peak 'fire season' differs depending on the region; for example, wildfires in the Southeast are more likely to occur in early spring or late fall. Although a few years old, this article highlights that the  Peak Wildfire Season Still Varies by State .

Wildfires are not a new problem and wildfires are not an exclusively a Western US or California problem. Over the years, every part of the country has had significant wildfire activities. When looking at historical fire losses there are several factors that make wildfires significant: lives lost, acres burned, and historical turning points.

The numbers of acres burned is a common metric for the significance of wildfires. In recent years the focus has been on the increasing size of wildfires.

The terminology has even changed in the popular media. Previously large wildfires were referred to as "Megafires" to highlight the scale. In recent years news reports have adopted the term "Gigafires"—that is fires burning over a million acres—to emphasize the growing scale of wildfire destruction.  Reuters  published a useful graphic highlighting this worrying trend (click on the image to scroll):

When we look further back in time we actually see more of a horseshoe-shaped distribution of very large wildfires. Many fires prior to the advent of active wildfire management practices in the past century were often in excess of 1 million acres. As we will see shortly in the  Significant Historical US Wildfires  section a series of devastating wildfires caused the federal government to formalize wildfire management policies. The first was known as the 'total fire suppression' ( Source ):

This policy had two goals: preventing fires, and suppressing a fire as quickly as possible once one started. [...] Forest Service leaders simply argued that any and all fire in the woods was bad because it destroyed standing timber. Educating the public about the need for fire prevention became an important part of this goal. [...] The other goal the Forest Service had was to develop a systematic approach to fire protection. In the decades following the Big Blowup, this would involve building networks of roads, communications systems, lookout towers, and ranger stations. To protect both federal and non-federal lands, the agency won passage of the Weeks Act of 1911, which in part established a framework between the federal government and the states for cooperative firefighting (the framework would later include private forest associations and landowners). By offering financial incentives to states to fight fires, the Forest Service came to dominate and direct what amounted to a national fire policy.

In the years that followed after continued major wildfires this policy of aggressive fire suppression was operationalized by the " 10 a.m. policy " instituted by the US Forest Service in the 1930s ( Source ):

Following several severe fire seasons in the early 1930s, fire suppression took on even greater urgency. In 1933, the federal government created the Civilian Conservation Corps, which put thousands of men to work building fire breaks and fighting fires. In 1935, the Forest Service established the so-called 10 a.m. policy, which decreed that every fire should be suppressed by 10 a.m. the day following its initial report. Other federal land management agencies quickly followed suit and joined the campaign to eliminate fire from the landscape.

This was the dominant wildfire management paradigm for most of the past century since the advent of the 10 a.m. policy. The focus has been on identifying wildfires as quickly as possible, sending as many resources as available, and suppressing the wildfire as soon as possible. And we were largely successful in reducing the number of acres burned year over year. Unfortunately, there was a dark side to that success. When wildfires did occur, they became increasingly destructive.

More recent research findings have led to another paradigm shift. We have learned that the unintended consequences of the 'total fire exclusion' has actually increased fire intensity and thus wildfire destruction. This is due in part to the increase of accumulated fuel (dense vegetation) that otherwise would have been burned off during more frequent, but less severe wildfires.

To understand the current wildfire problem, it is useful to look chronologically at some wildfires that not only burned many acres, destroyed many properties, and in some cases took many lives, but also had significant impact on wildfire policies, practices, and perceptions.

Previously, we introduced the fundamental fire science concept of the fire triangle that highlights the key elements required for a fire to occur but also help explain how to put out a fire. With wildfires researchers have developed a similar heuristic illustration known as the Wildfire Behavior Triangle.

In the following three sections we will outline and explain each leg of the triangle as it pertains to understanding wildfire behavior and wildfire risk.

When we put all of the science of wildfires together we can begin to understand how wildfires burns and how a combination of weather conditions and the landscape impacts fire behavior.

Fire science is not rocket science—it’s way more complicated.—Matt Dickinson, Research Ecologist, U.S. Forest Service - Northern Research Station

 Fire ecology  is a branch of ecology that focuses on wildland fires and their role within wider ecological systems, processes, and environments. Fire ecology focuses on fire adaptation within plant and animal species, fire history, fire regimes, and other effects on the wider ecosystems. One of the key findings is that different ecological regions experience similar types of fires in similar ways.

US Forest Service Ecologist Robert Bailey developed the concept of Ecological Regions or Ecoregions in the late 1970s. In the subsequent years he led a team that developed and expanded the concept across North America and beyond based on similar ecological biomes, landscape characteristics, and weather conditions (Click Here  For More Information ).

This illustration (below right) from the National Weather Service and NOAA weaves together many of the themes we discussed into one seamless graphic to explain how and why wildfires move as fast as they do, especially in the presence of strong winds and steep slopes.

Interestingly this graphic is actually an updated version of one developed for research published by Dick  Rothermel et al  in 1972 in the  first model of fire spread . While this original research was ground breaking it was also laboratory based and struggled to model more complex landscapes found in nature. But the scientific principles it distilled remain as true now as they were then.

When we hear about a report about a wildfire the size in the approximate acreage is almost always included to give a sense of how significant of a fire it is. But this focus on size often obscures the true threat posed by the fire. The relative location or proximity of the fire is harder to capture in a short news byte. Fires that occur in close proximity to the built environment are often far more important. A 500,000 acre fire in remote forests without any homes threatened is typically less of a concern than a 500 acre fire that is near or in a residential community.  

The more homes and structures that are built in close proximity to wildfire prone areas the greater the potential wildfire exposure. This is typically referred to as the Wildland Urban Interface or simply the WUI (pronounced: Woo-E). In the US there has been considerable expansion of the built environment in formerly undeveloped areas for a number of reasons, which has put a greater number of buildings at risk for wildfires. There are two main types of  WUI :

• Intermix WUI - the area where houses and wildland vegetation directly intermingle, with both a housing density > 1 house per 40 acres (6.17 houses/sqkm) and > 50% of the area in wildland vegetation
• Interface WUI - the settled areas abut wildland vegetation, with < 50% vegetation, but lie within 1.5 miles (2.5 km) of a densely vegetated area (> 75% wildland vegetation) that is at least 5 sqkm in size. Note that settlements near small urban parks are NOT included in WUI.

The [WUI] fire interface is any point where the fuel feeding a wildfire changes from natural (wildland) fuel to man-made (urban) fuel. For this to happen, wildland fire must be close enough for its flying brands or flames to contact the flammable parts of the structure (Butler, 1974, p. 3). The WUI has been variously defined as any area designated by the agencies that includes an interface/intermix community.

The SILVUS Lab at University of Wisconsin has mapped and classified the contiguous US to identify WUI areas and Intermix areas at  ten year increments , which helps illustrate how building developments are expanding in wildfire prone areas. The illustration below can be used to compare the map from 1990 to 2010 using the dynamic slider--click the arrows in the middle to compare the changes. The 2020 data is not yet available but is anticipated in the next year.

The wildfire threat in the  WUI is well-established . A  2018 study  found that 1/3 of homes are now being built in areas defined as WUI:

The vast majority of new WUI areas were the result of new housing (97%), not related to an increase in wildland vegetation. Within the perimeter of recent wildfires (1990–2015), there were 286,000 houses in 2010, compared with 177,000 in 1990. Furthermore, WUI growth often results in more wildfire ignitions, putting more lives and houses at risk. Wildfire problems will not abate if recent housing growth trends continue.

Worse yet, in WUI areas that have already experienced a wildfire many of the "lessons" are not being learned in terms of adopting stricter, wildfire resilient, building and zoning requirements, (with a  few exceptions ) "in the majority of cases there were no changes, and in some instances restrictions were actually reduced. The potential for learning and adaptation after fires just isn’t being fulfilled." ( Source )

One of the biggest questions for those watching the news about the latest wildfire and for wildfire experts alike is how and why do some homes burn during a wildfire. Perhaps it is best to turn that question around, why don't all homes burn during a wildfire? The popular conception that wildfires are a wall of flame that completely incinerates everything in its' path is more befitting a Hollywood blockbuster. In reality many homes destroyed in wildfires may have begun burning long before the flames of the wildfire arrive and may even burn long after the wildfire has passed. Often more puzzling is why some homes survive largely unscathed when all the vegetation and homes around them were destroyed.

The relatively simple question of "who is in charge of fighting wildfires" is anything but simple. It largely depends on where the fire initially started, the size of the fire, and the proximity to developed communities. There is no single unified entity, agency, or organization that is responsible for all wildfires in the US. There are many overlapping jurisdictions and there is considerable collaboration and occasional conflict among agencies. This complexity and overlap is important to understand the difficulty in answering equally  simple questions  like 'how many acres burned last year?' or 'how many wildland firefighters are there?' or even 'how much money was spent fighting wildfires last year?':

Data is currently entered into many unique systems. Basic fire information, such as location, size, environmental conditions, and resources, is often repeatedly entered into stand-alone systems as a foundation for their capabilities. [...] An example is the location of a fire (latitude and longitude). A 2008 interagency efficiency report identified that an interagency dispatcher may enter this piece of data up to 26 times into different systems. [...] When questions arise about individual fires, frequently, there are often multiple answers depending upon which data source is queried for the answer. While all of the answers may be valid in their specific context, there is no authoritative data source for a consistent answer. This presents a challenge for both the interagency fire community and line management at all levels of fire management agencies and departments.

These basic questions and our inability to answer them easily makes it difficult for decision makers in all sectors to determine the scope and scale of the wildfire problem and how to best address it.

In addition to the question of who is responsible for fighting wildfires, there is an interrelated question of how are wildfires fought? There are several types of wildfire firefighting resources that often utilize different types of tools, equipment, and vehicles.

For a century the prevailing thinking was the best way to prevent the destruction of property and loss of lives from wildfire was to aggressively suppress them at the first indication of a wildfire. Those assumptions have come under  increasing scrutiny  but the problem remains, how to protect people and property from wildfires. The key factor now is aggressive, coordinated, and ongoing wildfire mitigation efforts to reduce the likelihood of damage from a wildfire and increase the survivability of buildings. This started with raising awareness of the threat posed by wildfires and encouraging local community members to do their part.

The primary challenge of wildfire mitigation is ensuring that property owners understand their risk of wildfire and thus have some motivation to address that risk. Educating the general public about the importance of preventing wildfires has been ongoing for better part of a century including the  iconic Smokey Bear campaigns  first introduced in 1944. While Smokey Bear is among the most recognized and  successful advertising campaigns in history , those types of generalized messages do not give the general public specific, localized, and actionable information about their specific risks and risk mitigation strategies.

For too long that level of knowledge was predominantly the preview of experts, wildfire practitioners, and scientists. In the past few decades there has been increasing efforts to translate the latest findings from scientific research and field experience into ever more digestible and actionable insights.

In 2019 the US Forest Service launched a new, easy-to-understand, and actionable tool called  Wildfire Risk to Communities  that consolidated all of their available data, research, and best practices in a single platform.

Click on the interactive map tool above and you can change the location and you can explore the various information available. The link below will open up the same resource in a separate browser to explore the tool and information in more depth.

Every year there are more resources available that help better understand the wildfire problem. Yet with the additional information occasionally comes information overload. Maps are an effective way to share this information. ESRI has overlaid a number of useful datasets to highlight various aspects of wildfire risk and exposure. (These maps may require an ESRI account to view)

As noted previously, traditionally there was an assumption that when wildfires approached buildings it was a wall of flames that completely consumed everything in its path. And certainly that can and does occur on occasion. This traditional assumption was somewhat fatalistic, as it tended to also assume there is nothing that can be done to save a building if a wildfire approached it. In the past few decades, as wildfire science and research has advanced, we have realized that building construction practices and vegetation management efforts have a dramatic impact on the survivability of a building. This is especially true when these efforts are done at community scale.

The best approach is often when the property owner starts with their building and then move outwards from there. While it is easy to focus on how to build the ideal wildfire resistant building from scratch, for owners with existing buildings there are some practical and important changes they can make to their home with moderate costs to increase the survivability of their home. Research by  Alexandre et al  noted regional differences when looking at those homes that survived exposure to wildfire, they specifically noted that in certain ecoregions localized fuel mitigation was enough to prevent many home ignitions but in other ecoregions the fire behavior was likely to be more significant limiting the benefit of fuel mitigation alone.

If there is one take away about wildfire mitigation that should be clear by this point, wildfire mitigation must include a multi-pronged approach. There are many mitigations that property owners can and must do to reduce their own exposure. Property owners must work collectively as a neighborhood to reduce their collective exposure. Local, state, and even the federal government have an equally important role in terms of larger scale efforts to reduce wildfire exposure. Many of the larger macro level approaches tend to focus on reducing the fuel that feeds wildfires--natural vegetation of all types, sizes, and locations.

We tend to focus on wildfire mitigation efforts that occurs months or years ahead of a wildfire approaching a community. But sometimes the wildfire mitigation that makes the most impact occurs in the minutes and hours before a wildfire reaches a property. This sort of last minute triage blurs the line between mitigation and suppression but can be the difference between a building surviving and not.

There is considerable wildfire terminology to learn. This resource is a relatively comprehensive list:  https://www.fs.fed.us/nwacfire/home/terminology.html  For the purposes of the Risk Awareness Service we have included some common definitions that you may encounter when reading this document.

Backfire - A fire deliberately set by firefighters along the inner edge of a fireline--a gap, path, road, or river--to consume the fuel in the path of a wildfire and/or change the direction of force of the fire's convection column.

Campaign Fire — A wildfire of such size, complexity and/or priority that its extinction requires a large organization, high resource commitment, significant expenditure, and prolonged suppression activity.

Complex Fire - Increasingly fires are being given names like the Mendocino Complex Fire or the CZU or SCU Complex Fire. Definition: “Two or more individual incidents located in the same general area which are assigned to a single incident commander or unified command.” Sometimes these adjacent fires may never merge but often they will eventually merge together and become one single large ‘complex’ fire. For example: the Mendocino Complex Fire consisted of two fires, Ranch Fire and River Fire, in close proximity to one another that never merged, but both were among some of the largest fires in California history, at the time.

Crown Fires - Fire that has ascended from the ground into the forest canopy. Crown fires typically move rapidly from tree top to tree top and are typically particularly destructive for the trees which might otherwise be able to survive a fire closer to their base.

Embers - Small, glowing pieces of superheated wood or other carbonaceous material that are generated by or remain after a fire. Embers can remain smoldering for hours or days depending on ambient conditions and how well insulated they are and can cause (re)ignition of surrounding flammable materials far ahead of or long after a fire passes. (see also: Fire Brands)

Fire Brands - Are a type of ember that are lofted into the air and can travel hundreds of feet and even upwards of a mile. When fire brands land on combustable materials or enter homes through unprotected vents, exposed rafters or compromised openings they can cause ignitions and spot fires far ahead of a wildfire. Research has shown that embers and fire brands are responsible for upwards of 90% of home ignitions in wildfires.

Flame Front - The zone at a fire’s edge where solid flame is maintained flaming front. 

Initial Attack - These are the actions taken by the first resources to arrive at a wildfire to protect lives and property, and prevent further extension of the fire. 

Megafire - A colloquial term for large-scale wildfires that burn more than 100,000 acres. In recent years this term has been eclipsed by Gigafires to describe wildfires of more than 1 million acres.

Spot Fire - A smaller fire that has started from sparks and brands thrown in the spot fire air by the main fire.

Wildland-Urban Interface (WUI) - Zone where structures and other human developments meet, or intermingle with, undeveloped wildlands. (for more information see the subsection on WUI in the Science of Wildfires.)

Pre-eminent fire historian  Stephen Pyne  has a number of books, public lectures, and resources about wildfire, both in the US and on every continent. This  summary  about wildfire he produced for the media closely aligns with the material outlined here.

The Insurance Information Institute (Triple I) has a number of useful resources about wildfire losses and exposures  here  and in their annual Fact Book.