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Wildland Urban interfaces (WUI) are facing dangerous fire threats

Wildland-urban interfaces (WUI) are areas where dense urban development meets and intermingles with wildland vegetation. WUIs are created through building new houses and other structures near the natural environment, or through the regrowth of new vegetation in developed lands. As beautiful as it is to have greenery surrounding a community, vegetation overgrowth, and dense trees pose a fire hazard for these communities. Understanding the issue of growing WUI in a time when wildfires are becoming more frequent and intense, is critical to better understand the economic costs that we will continue to see in a changing climate. As people continue to settle in these wildland-urban interfaces, understanding the fire risks associated with living in these zones is crucial.


The affordable prices and desire to live near the beauty of a natural environment where wildland vegetation is growing around houses are the main attractions bringing more people into WUI, despite the zone being a wildfire hazard. California has the most WUI homes, with 4 million residencies since 2010. As populations in the nation continue to grow and settle into these interfaces, many homes will face dangerous threats posed by wildfires. A recent 2018 research article, “Rapid growth of the US wildland-urban interface raises wildfire risk” used census data to determine how much WUI in the United States occurred from 1990 to 2010. From that time period, there were 12.7 million residencies adjacent to vegetation wildlands and although WUI only made up less than 0.1% of the U.S.’ land area, 43% of new houses were built on this land. This expansion of urban development into regions with dense vegetation is inevitable, but knowing how settlement into these areas is fueling fires and influencing their spread is important to understand.

Figure 1: The Oak Fire outbreak last Friday July 22, 2022 is now intense and fast-moving and is now burning into the wildland-urban interface, with some level of structure loss already. Image source: Los Angele Times

In an unprecedented climate of high temperatures, extreme weather conditions, and increased wildfire risks and severity, these communities have become vulnerable and more susceptible to experiencing dangerous fire spread. Of the wildfires that California has experienced, some of them have overlapped with WUI. Fires in these particular areas are escalating the cost of fire suppression and community recovery. One of the fires that blazed through a WUI community is the Tubbs Fire. The wildfire raged through Northern California where 14,895 hectares were burned and more than eighteen thousand structures were lost. The Tubbs fire caused more destruction in urban areas, but most of the structures lost were those located in the WUI. The cost alone to suppress this fire was $100 million.


Succeeding the damages caused by the Tubbs fire, the 2018 Camp Fire, known infamously for being the most destructive and deadliest wildfire in California history, destroyed the small town of Paradise and forced residents to evacuate and leave everything behind. In just 6 hours, the wildfire burned 90% of the small town. The inferno burned through 62,053 hectares and destroyed 18,804 structures, caused 85 fatalities and resulted in over $16 billion in damages. These are only two of the many large and out-of-control wildfires that WUI communities in California have had to deal with recently. Fire suppression expenditures in California have reached an annual cost of $2 billion and in 2018 over $150 million of that spending was used to battle the CampFire.


Dense community development built along wildlands contributes vastly to the large fire suppression expenditures in the WUI. With acquired data from WUI fires from 2008 to 2010, the Forest Service released an audit concluding that the cost to fight fires in the WUI amounted to $1695 per acre. A mix of High winds and dry conditions with poor land management is increasing the size and scope of fires happening in the interface. The costs associated with wildfires are exceedingly high and will only continue to increase alongside temperatures.

Figure 2: The Marshall fire in Colorado started on Dec 30, 2021 burned more than one thousand structures in WUI, including houses, a hotel, and at least one shopping center. Image source: Wikimedia Commons

Recovery efforts following catastrophic fires will be far more expensive than the funds used to mitigate, contain, and suppress them. Recovery expenditures can cover anything from the costs of debris removal to housing and community development to the rebuilding and repair of infrastructure. Towns like Paradise are having to rebuild most of their communities from nothing and some residents may not even return to the town. A recent literature analysis based on 5 wildfire case studies found that just 9% of the funds allocated to cover wildfire costs are used in fire suppression efforts, while the rest is used to recover from short and long-term damages such as aid relief, landscape rehabilitation, housing and community development. In addition to these recovery costs, volunteer efforts to clean up and restore the community are common. This is a long process and requires thousands of hours of unpaid labor by those who want to help with community recovery. 

Although it may be affordable to settle in some WUIs, these wildfires have proven otherwise. Living there turns out to be more costly because WUI communities are susceptible to heavy wildfire impacts. The surrounding vegetation, if not managed, is overgrown and fire-prone plant species only create higher fire risks. Areas with dense vegetation and dry shrubs are accelerating the spread of fires. Human ignited fires are common and oftentimes, those fires may be ignited by nearby power utility equipment or even tiny embers from human activities. In recent years, eight of the 20 most disastrous wildfires that California has experienced were caused by utility equipment, including the Tubbs and Camp Fire. A tree fall could result in a downed power line and ultimately cause a fire that spreads quickly from vegetation and is intensified by extreme weather conditions. Although the origin of a fire could be from power equipment, poor fuel and land management are also large contributors to these fires.

Current fire suppression methods used today continue to make this problem worse because large amount of biomass is often fueling subsequent fires. 

Homeowners can take action to prepare their homes in efforts to reduce the spread of fire to their homes. Designing the landscape of homes and buildings to be fire resilient significantly will reduce fire dangers and impacts the survivability of a home. Homeowners can create or maintain a defensible space by reducing dense vegetation and small trees near the perimeter of a residence, thinning out trees and bushes, and removing dead vegetation. Putting away other flammable material that may lay around a person’s yard like propane tanks, power tools, or woods as well as any household hazards. Additionally, upgrading house vents with metal mesh screens will keep small embers from entering homes and installing wildfire detection systems to detect early smoke may make all the difference in catching the danger earlier. While these are only to minimize the risk of fire, homeowners should also be prepared in the case that a wildfire is approaching their community. They should have a robust plan of action in the case of a fire. Assessing which evacuation routes will be accessible during a dangerous fire situation will be crucial. Combining the removal of any and all fire hazards and monitoring the nearby landscape for potential dangers will reduce the risk of fire to residences in the WUI. There are many ways in which residents can prepare themselves to prevent these disasters. Of course, the risk of fire will only continue to increase, but taking these measures is important to reduce the growing threat of fire hazards within the WUI.

The expansion of WUI and the effects of climate change is a combination that exacerbates the damage caused by wildfires. For this reason, homeowners must take mitigation measures and understand the importance of early fire preparation. They should hold knowledge of what the risks of living in the wildland-urban interface consist of and what they should do in order to prevent the losses that wildfires may cause them.



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