Wildland Urban Interface Communities Research Articles

WUI-PEM: Wildfire Phased Zone Evacuation Methodology

Wildfires are a growing threat to wildland-urban interface (WUI) communities. Globally over the last decade hundreds of wildfire related deaths have occurred along with hundreds of billions in economic losses. If the encroachment of fire into a community cannot be stopped, evacuation becomes necessary to save lives. In response to the increasing threat, WUI communities must properly prepare and implement an evacuation plan, as orchestrating an evacuation within a limited time frame is a complex challenge. While several fire and evacuation simulation tools have been developed to aid planning, a comprehensive methodology for constructing and assessing evacuation plans is still evolving. This article fills some of the current gaps with a simple six-step process to evaluate wildfire risk, individual evacuation zone traffic demand, and formulate a staged zone-based full evacuation plan. This methodology can be used for wildfire evacuation planning, evacuation plan management, and training.

Integrating dynamic wildland fire position input with a community fire spread simulation: A case study of the 2018 Camp Fire

Wildland fire simulation models can be used to inform wildfire risk assessment and mitigation strategies. However, existing models tend to simulate fire spread only inside the wildland or the wildland-urban interface (WUI) communities, but not in both. As a result, there is a need to integrate methodologies to enable seamless simulations of events that ignite in the wildland and continue spreading both across the wildland and inside WUI communities. This paper investigates a systematic methodology to provide a WUI fire spread model with the capacity to assimilate dynamic wildland fire position inputs. The paper uses the streamlined wildland-urban interface fire tracing (SWUIFT) model to simulate WUI fire spread, weather radar data to track the fire line inside the wildland, and the 2018 Camp Fire event as a case study. The work proposes and evaluates a methodology based on a ‘Three-Domain Solution’ (Wildland, Transition, Community) for a smooth fire transition between wildland and community settings. Alternative approaches are examined to describe the boundaries of a Community Domain for simulation purposes. Existing WUI definitions are studied, and considering the analysis results, a non-WUI neighborhood-based housing density (NBHD) method is proposed. This work establishes a systematic approach for a unified wildland-WUI fire simulation.

Analyzing Risk Perception, Evacuation Decision and Delay Time: A Case Study of the 2021 Marshall Fire in Colorado

Climate change is increasing the threat of wildfires to populated areas, especially those within the wildland-urban interface (WUI). The 2021 Marshall fire forced the evacuation of over 30,000 people in Boulder, Jefferson and Adams Counties in Colorado, US. To improve our understanding of wildfire evacuation response, we surveyed individuals affected by the Marshall fire to analyze their evacuation decisions and resulting behavior. We used linear and logistic regression models to determine the factors influencing individuals’ risk perceptions, their decisions to evacuate or stay, and the associated evacuation delay times. We found higher levels of risk perception at the time of the evacuation decision were associated with higher levels of pre-fire perceived risk, having mid-level household income, the receipt of fire cues and having a medical condition. Increased pre-event risk perception increased the likelihood of evacuating, along with gender (female-identified), being aged between 55 and 64 years, and having a higher household income. On the other hand, having a prior awareness of wildfires had a negative effect on evacuation likelihood. Additionally, having previous experience with fire damage, owning their home, having a larger household size and being alerted later in the fire event reduced the delay time; whereas engaging in preparation activities and having children in the home led to longer delay times. These research findings can be used by emergency managers to better prepare WUI communities for future wildfire events.

CFD informed design of bench-scale experiments to characterize air entrainment into fuel beds induced by columnar vortices

Recent experiments show that strong vortices, similar to fire whirls, can form far from a fire front in the region of smoldering fuel. These buoyancy-induced columnar vortices, visualized by entrained smolder smoke, were observed lofting hot embers into the air and in some cases lead to spot ignitions at the base of the vortex. Gaining insight on how the flow field of a buoyancy-induced columnar vortex could impact surrounding smoldering fuel is the focus of this study. Specifically, the potential air entrainment into a fuel substrate beneath the vortex. The flow field of such columnar vortices has been shown to drive air flow downward under certain conditions and, in the context of combustion, drive air deeper than typical entrainment, inducing spot ignitions and increasing burning and smolder rates. NIST's Fire Dynamics Simulator is utilized to successfully model buoyancy-induced columnar vortices. Then it is utilized to study the behavior of vortices as temperature and vorticity boundary conditions are changed. The flow field and fresh air entrainment potential are analyzed. The simulation results inform the experiment design and preliminary experimental results are presented. Understanding these high-risk phenomena will lead to better risk mitigation and more resilient Wildland-Urban interface communities.

Exploring and Testing Wildfire Risk Decision-Making in the Face of Deep Uncertainty

We integrated a mechanistic wildfire simulation system with an agent-based landscape change model to investigate the feedbacks among climate change, population growth, development, landowner decision-making, vegetative succession, and wildfire. Our goal was to develop an adaptable simulation platform for anticipating risk-mitigation tradeoffs in a fire-prone wildland–urban interface (WUI) facing conditions outside the bounds of experience. We describe how five social and ecological system (SES) submodels interact over time and space to generate highly variable alternative futures even within the same scenario as stochastic elements in simulated wildfire, succession, and landowner decisions create large sets of unique, path-dependent futures for analysis. We applied the modeling system to an 815 km2 study area in western Oregon at a sub-taxlot parcel grain and annual timestep, generating hundreds of alternative futures for 2007–2056 (50 years) to explore how WUI communities facing compound risks from increasing wildfire and expanding periurban development can situate and assess alternative risk management approaches in their localized SES context. The ability to link trends and uncertainties across many futures to processes and events that unfold in individual futures is central to the modeling system. By contrasting selected alternative futures, we illustrate how assessing simulated feedbacks between wildfire and other SES processes can identify tradeoffs and leverage points in fire-prone WUI landscapes. Assessments include a detailed “post-mortem” of a rare, extreme wildfire event, and uncovered, unexpected stabilizing feedbacks from treatment costs that reduced the effectiveness of agent responses to signs of increasing risk.

Toward Probabilistic Risk Assessment of Wildland–Urban Interface Communities for Wildfires

Toward Probabilistic Risk Assessment of Wildland–Urban Interface Communities for Wildfires

Behavior of Service Lateral Pipes during Wildfires: Testing Methodologies and Impact on Drinking Water Contamination

Wildfires have damaged civil infrastructure throughout wildland urban interface communities, including water distribution systems. Post-wildfire, communities have detected volatile organic compounds (VOCs) within drinking water systems. This paper focuses on the behavior of service lateral pipes used for potable water under fire conditions, with an emphasis on testing methodologies and impacts on drinking water contamination. The authors tested commonly-used service lateral pipes (type L copper, galvanized steel, schedule-40 PVC, and STIR-7 HDPE) at elevated temperatures to determine critical threshold temperatures at which these pipes thermally degrade. This paper summarizes tests evaluating type L copper, galvanized steel, schedule-40 PVC, and STIR-7 HDPE pipe materials at elevated temperatures and numerical simulations to examine fire scenario characteristics that may thermally degrade pipes. Post-heating treatments of the pipes were considered (spirals, small pieces, and whole sections) to examine the influence of different testing methodologies on the contamination levels found in water, primarily how the surface area exposed influences the concentration of contaminants during a fire. Water was analyzed following EPA 524.2, and regression curves were fitted to the results to quantify the threshold temperatures at which pipe materials may release VOCs exceeding federal limits. Practical metrics, including wildfire conditions (heat flux and burn duration) and pipe burial depths, were varied to investigate under what circumstances buried service laterals may exceed threshold temperatures. From the series of tests performed, the authors conclude that neither galvanized steel nor copper released VOCs exceeding the federal limit at the highest tested temperature (300 °C) and that the threshold temperatures for PVC and HDPE were 194 and 254 °C, respectively. Additionally, results show that the surface area of pipe materials tested does affect contamination levels; however, regardless of the surface area tested, the heating of relatively short lengths of pipe (less than 3.25 m) can release contaminants exceeding federal limits.

A burning issue: Reviewing the socio-demographic and environmental justice aspects of the wildfire literature.

Larger and more severe wildfires are becoming more frequent and impacting different communities and human settlements. Much of the scientific literature and media on wildfires has focused on area of ecosystems burned and numbers of structures destroyed. Equally unprecedented, but often less reported, are the increasing socioeconomic impacts different people and communities face from wildfires. Such information seems to indicate an emerging need to account for wildfire effects on peri-urban or wildland urban interface (WUI) areas, newer socio-demographic groups, and disadvantaged communities. To address this, we reviewed the socio-demographic dimensions of the wildfire literature using an environmental justice (EJ) lens. Specifically using a literature review of wildfires, human communities, social vulnerability, and homeowner mitigation, we conducted bibliometric and statistical analyses of 299 publications. The majority of publications were from the United States, followed by Canada and Australia, and most dealt with homeowner mitigation of risk, defensible space, and fuel treatments in WUI areas. Most publications studied the direct effects of wildfire related damage. Secondary impacts such as smoke, rural and urban communities, and the role of poverty and language were less studied. Based on a proposed wildfire-relevant EJ definition, the first EJ publication was in 2004, but the term was first used as a keyword in 2018. Studies in WUI communities statistically decreased the likelihood that a publication was EJ relevant. There was a significant relationship between EJ designation and inclusion of race/ethnicity and poverty variables in the study. Complexity across the various definitions of EJ suggest that it should not be used as a quantitative or binary metric; but as a lens to better understand socio-ecological impacts to diverse communities. We present a wildfire-relevant definition to potentially guide policy formulation and account for social and environmental justice issues.

Estimating wildfire evacuation decision and departure timing using large-scale GPS data

Recently, wildfires have created severe challenges for fire and emergency services and communities in the wildland-urban interface (WUI). To reduce wildfire risk and enhance the safety of WUI communities, improving our understanding of wildfire evacuation is a pressing need. This study proposes a new methodology to analyze wildfire evacuation by leveraging a large-scale GPS dataset. This methodology includes a proxy-home-location inference algorithm and an evacuation-behavior inference algorithm, to systematically identify different groups of wildfire evacuees (i.e., self-evacuee, shadow evacuee, evacuee under warning, and ordered evacuee). We applied the methodology to the 2019 Kincade Fire in Sonoma County, CA. We found that among all groups of evacuees, self-evacuees and shadow evacuees accounted for more than half of the evacuees during the Kincade Fire. The findings of this study can be used by emergency managers and transportation planners to better prepare WUI households for future wildfire events.

Effects of spacing on flaming and smoldering firebrands in wildland–urban interface fires

Firebrand (ember) attack has been shown to be one of the key mechanisms of wildfire spread into wildland–urban interface communities. After the firebrands land on a substrate material, the ignition propensity of the material depends on not only the attributes (e.g. shape, size, and numbers) but also the distribution of the firebrands. To help characterize this process, this study aims to investigate the effects of gap spacing on the burning behaviors of a group of wooden samples. Experiments are conducted using nine wooden cubes, 19 mm on each side. These samples are arranged in a 3 × 3 square pattern on suspension wires and are ignited by hot coils from the bottom surface. The gap spacing (s) between the samples varies in each test (ranging from 0 to 30 mm). After ignition, the samples are left to burn to completion. The burning process is recorded using video cameras. Sample mass loss and temperatures are monitored during the flaming and smoldering processes. The results show that the flame height and the sample mass loss rate have non-monotonic dependencies on the gap spacing. When the gap spacing reduces, the flame height and the mass loss rate first increase due to enhanced heat input from the adjacent flames to each sample. When s ≤ 10 mm, flames from individual samples are observed to merge into a single large fire. As s further decreases, the air entrainment at the flame bottom decreases and the flame lift-off distance at the flame center increases, resulting in an increased flame height, decreased flame heat feedback to the solid samples, and a decreased mass loss rate. The decreased mass loss rate eventually leads to a decrease in the flame height as well. The gaseous flame height is correlated to the solid burning rate. The correlation generally follows previous empirical equations for continuous fire sources. For the smoldering combustion, compared to a single burning sample, the smoldering temperature and duration significantly increase due to the thermal interactions between adjacent burning samples. To help interpret the results of the burning experiments, thermogravimetric analysis is also performed in air and nitrogen, resulting in heating rates ranging from 10 to 100 K/min.

Streamlined wildland-urban interface fire tracing (SWUIFT): Modeling wildfire spread in communities

The wildland-urban interface (WUI) is defined as a geographic area where human developments and flammable vegetation merge in a wildfire-prone environment. Losses due to wildfire have been rising in the past decade, attributed to changes in vegetation growth, fuel availability, and increased land developments in WUI. This paper studies the process of wildfire spread inside WUI communities. The fire spread rate within WUI communities is determined for nine wildfires that were ranked among the most destructive wildfires in North America. An improved quasi-empirical model that considers radiation and fire spotting as modes of fire spread inside a community is proposed. The new model is validated using the documented spread rates during the 2007 Witch and Guejito fires and the 2017 Tubbs fire. The proposed model is computationally efficient and can be used to quantify fire spread rate and the number of affected structures inside a community during a wildfire event.

Homeowner perceptions and responses to buffelgrass invasion risk in the Tucson, Arizona Wildland-Urban Interface

In this study, we aimed to analyze homeowners' level of awareness and perceived risk about buffelgrass invasion in the Tucson, Arizona Wildland-Urban Interface (WUI), as well as the factors influencing their participation in buffelgrass control and fire risk mitigation efforts. Data for the study were generated through the administration of an online survey among 117 members of Home Owner Associations (HOAs) in the Tucson WUI. The results showed that the overwhelming majority of respondents were aware of buffelgrass, but their knowledge about buffelgrass control mechanisms appeared to be limited. Respondents also more frequently expressed concern about the risks posed by buffelgrass invasion to general targets, such as the Sonoran Desert ecosystem, native plants and wildlife than risks to their private property and neighborhoods. The results also showed that the level of involvement in HOAs, and leadership in HOAs had significant positive effects on homeowners' participation in buffelgrass control efforts. Homeowners' duration of residence also had a significant negative effect on participation in buffelgrass control efforts, suggesting that newcomers may be more involved than long-term residents. Similarly, the number of months respondents spent in Tucson per year had a negative effect on the number of hours spent on buffelgrass control efforts. Respondents’ perceived risk about buffelgrass invasion also had a positive effect on the hours spent on buffelgrass control as well as their level of involvement in fire risk mitigation efforts. These results highlight the importance of local institutions and community heterogeneity in social responses to threats in WUI communities. Policies aimed at building the resilience of WUI communities need to account for their complexity as coupled social-ecological systems.

Fire Hazards at the Wildland Urban Interface: a Perspective from the Wuiview Project

Wildland Urban Interface (WUI) fires are posing tremendous management challenges in terms of civil protection and fire mitigation. Many critical factors are contributing and increasing the risk at the WUI, such as the presence of all sorts of fuels whose hazard is poorly characterized and disregarded by residents, the existence of vulnerable elements in houses and industrial installations and the absence of standards that deal with the WUI problem at the homeowner/ property scale. The WUIVIEW project aims at developing an innovative risk management tool that will help WUI communities to adapt in order to face the new generation of forest fires. This is being done by designing, setting up and testing a virtual workbench service for the performance-based analysis of fire environments in the surroundings of buildings at the WUI. In this framework, a methodological approach for the assessment of LPG domestic tanks vulnerability under fire exposure at the WUI has been developed. The present work provides a demonstration of such methodology through a realistic case study, together with an overview of the WUIVIEW project activities.

The simulation of wildland-urban interface fire evacuation: The WUI-NITY platform

Wildfires are a significant safety risk to populations adjacent to wildland areas, known as the wildland-urban interface (WUI). This paper introduces a modelling platform called WUI-NITY. The platform is built on the Unity3D game engine and simulates and visualises human behaviour and wildfire spread during an evacuation of WUI communities. The purpose of this platform is to enhance the situational awareness of responders and residents during evacuation scenarios by providing information on the dynamic evolution of the emergency. WUI-NITY represents current and predicted conditions by coupling the three key modelling layers of wildfire evacuation, namely the fire, pedestrian, and traffic movement. This allows predictions of evacuation behaviour over time. The current version of WUI-NITY demonstrates the feasibility and advantages of coupling the modelling layers. Its wildfire modelling layer is based on FARSITE, the pedestrian layer implements a dedicated pedestrian response and movement model, and the traffic layer includes a traffic evacuation model based on the Lighthill-Whitham-Richards model. The platform also includes a sub-model called PERIL that designs the spatial location of trigger buffers. The main contribution of this work is in the development of a modular and model-agnostic (i.e., not linked to a specific model) platform with consistent levels of granularity (allowing a comparable modelling resolution in the representation of each layer) in all three modelling layers. WUI-NITY is a powerful tool to protect against wildfires; it can enable education and training of communities, forensic studies of past evacuations and dynamic vulnerability assessment of ongoing emergencies.

Fire evacuation modelling of a Canadian wildland urban interface community

Wildland urban interface (WUI) communities are situated at the interface between human development and wildland fuel. In addition to their proximity to susceptible regions, routes of evacuation in WUIs are often limited, posing great risks to these communities in the event of a natural disaster. Considering the abundance of WUI interfaces in Canada, Canadian-based research is vital for developing national wildfire regulations. However, the limited amount of Canadian research forces authorities to seek wildfire evacuation techniques from foreign sources, which may not be proven to be effective in northern boreal forests. To begin the research herein, a Canadian WUI community in central Canada was selected as a case study to investigate assembly and evacuation patterns during a fire evacuation to illustrate the complexity of the situation and the current research needs required. First-stage simulations of evacuations were performed in the traffic simulation software PTV VISSIM, which extracted useful data, including evacuation times and related parameters. The results demonstrated that the addition of an extra highway access road reduces evacuation times by up to an hour and 20 minutes, which can determine whether a resident evacuates or not. However, the predictive power of the software is limited by its ability to incorporate the effects of human behaviour and the fire behaviour itself. Thus, extending these findings to include the need for evacuee behaviour and fire dynamics is a crucial second stage in the formation of a more complete strategic evacuation plan for communities at risk of wildfires. This study is vital for creating a Canadian-based approach to WUI wildfire evacuations and to expand the knowledge base in the field.

Prediction of Water Distribution System Contamination Based on Wildfire Burn Severity in Wildland Urban Interface Communities

The devastation to infrastructure in wildland urban interface (WUI) communities caused by wildfires has brought attention to the dramatic and unforeseen impacts of high fuel load density within the...

The “Strings Attached” to Community Difference and Potential Pathways to Fire Adaptiveness in the Wildland Urban Interface

AbstractThis article identifies specific social characteristics in two wildland urban interface communities that may have significant impacts on the ability of those communities to adapt to wildfire. Researchers used a mixed-methods approach to triangulate results to identify potential views and motives surrounding three important behaviors and values related to crafting potential strategies to mitigate wildfire risk. The analysis of quantitative data in the form of responses to Likert-type questions and qualitative data in the form of responses to questions asked during focus group sessions yielded a deeper understanding of the way the terms independence and trust are conceptualized from one community to another. Understanding what these concepts mean in the context of a given community is essential to understanding how to move forward with strategies to reduce risk and eliminate potential barriers to doing so.

WUI fire risk mitigation in Europe: A performance-based design approach at home-owner level

Fires at the Wildland-Urban Interface (WUI) are becoming increasingly hazardous for life safety and property protection. Guidelines and standards for fire practitioners are needed in order to help WUI communities face this threat and become fire-adapted. A performance-based design approach (PBD) is proposed to deal with the complex issues present at the WUI homeowner scale, which entails the use of Computational Fluid Dynamics (CFD) tools such as FDS in order to identify vulnerabilities in a quantitative manner. An analysis of recent European WUI fires is presented, along with the definition of several pattern scenarios that can be derived from these. Based on this analysis, examples of PBD fire scenarios specific for the Mediterranean WUI microscale are presented, involving glazing systems, roofing and gutters, external structures adjacent to the main building, and gaps present in the building envelope. A worked example to show the implementation of the proposed PBD method is provided in which the fire impact of residential fuel on a glazing system is quantitatively analysed.

Wildfire impacts on schools and hospitals following the 2018 California Camp Fire

Wildfire impacts on communities have become more pronounced in recent years as the intensity and frequency of wildfires have increased in densely populated areas of the USA. Communities located in the wildland–urban interface (WUI) neighboring high wildfire risk zones are at highest risk of damage to civil infrastructure. This paper summarizes an investigation on the 2018 Camp Fire impacts to schools and healthcare facilities in Paradise, CA. The paper demonstrates that interdisciplinary data collection methods can provide a comprehensive overview of school and hospital damage after a wildfire. Photographs, light detection and ranging (LiDAR) scans of damaged buildings, drone aerial images, and interviews with key school and healthcare stakeholders provided valuable information on the structural and nonstructural damages to infrastructure. Interviews also provided context to the impacts of infrastructure damage on the ability of education and healthcare facilities to operate or reopen following the fire. Nonstructural damage to schools and hospitals, such as damage to electrical systems or other utilities, significantly impacted the functionality of these facilities. Understanding the vulnerabilities of WUI communities to wildfire will help with disaster mitigation and recovery planning and aid in restoring critical services after the disaster.

Identifying opportunities for the use of broadcast prescribed fire on Colorado’s Front Range

Increasing the pace and scale of fuel treatments to protect social and ecological values from severe wildfire is a major initiative of numerous land management agencies, organizations, and collaborative groups throughout the western United States, including the Colorado Front Range. Broadcast prescribed fire is a relatively low-cost, effective management tool for achieving fuels reduction at scale but is often challenging to implement due to complex socio-ecological factors. We present results of a multi-criteria suitability analysis intended to identify need, opportunities, and constraints for the use of broadcast prescribed fire on Colorado’s Front Range based on spatial factors including wildfire hazard, vegetation and fuel types, historical fire regimes, presence of existing fuel treatments, wildland-urban interface development, and predicted prescribed fire behavior. Within our 1.7 million-hectare (ha) analysis area, over 228,000 ha (approximately 13%) were classified as highly suitable for broadcast prescribed fire. Areas of high suitability were split roughly 50:50 between public federal lands (5.3%) and private lands (6.1%), emphasizing the importance of implementing prescribed fire across ownerships to meet management objectives at scale. Patch size analysis revealed opportunities for large-scale (>500 ha) prescribed fire projects spatially distributed throughout the Front Range. These areas may serve as anchors for developing projects focused on protecting values at risk, including wildland-urban interface communities and water resources. Results of this analysis can be used in collaborative settings to develop comprehensive fuels reduction and forest restoration strategies that incorporate the use of prescribed fire, including identifying where mechanical treatments could be applied on the landscape to facilitate the use of broadcast prescribed fire over large extents, as well as where prescribed fire may be a viable option for long-term maintenance of treatments. While our analysis focuses on the Colorado Front Range, it can be replicated in other fire-prone areas of the western United States based on the availability of local data.