Wildland-urban Interface Research Articles

Assessing Fire Risk in Wildland–Urban Interface Regions Using a Machine Learning Method and GIS data: The Example of Istanbul’s European Side

Like many places around the world, the wildland–urban interface areas surrounding urban regions are subject to variable levels of fire risk, threatening the natural habitats they contact. This risk has been assessed by various authors using many different methods and numerical models. Among these approaches, machine learning models have been successfully applied to determine the weights of criteria in risk assessment and risk prediction studies. In Istanbul, data have been collected for areas that are yet to be urbanized but are foreseen to be at risk using geographic information systems (GIS) and remote sensing technologies based on fires that occurred between 2000 and 2021. Here, the land use/land cover (LULC) characteristics of the region were examined, and machine learning techniques, including random forest (RF), extreme gradient boosting (XGB), and light gradient boosting (LGB) models, were applied to classify the factors that affect fires. The RF model yielded the best results, with an accuracy of 0.70, an F1 score of 0.71, and an area under the curve (AUC) value of 0.76. In the RF model, the grouping between factors that initiate fires and factors that influence the spread of fires was distinct, and this distinction was also somewhat observable in the other two models. Risk scores were generated through the multiplication of the variable importance values of the factors and their respective layer values, culminating in a risk map for the region. The distribution of risk is in alignment with the number of fires that have previously occurred, and the risk in wildland–urban interface areas was found to be significantly higher than the risk in wildland areas alone.

Wildfire-Residential Risk Analysis Using Building Characteristics and Simulations to Enhance Structural Fire Resistance in Greece

Urban areas adjacent to wildlands are very dangerous zones for residents and their properties during a wildfire event. We attempted to connect wildfire simulations with field inventories and surveys to create a framework that can be used to enhance the fire resistance of residential structures located in the wildland-urban interface (WUI). Legal restrictions and the lack of economic incentives for WUI residents greatly limit the potential to appropriately intervene to enhance their property’s fire resistance. By studying in situ the resilience of building materials and combining them with exposure metrics produced from wildfire simulations, we created an index that helps to assess fire risk at the property level. The proposed index can support property owners to optimally manage the vegetation near or inside their property. State agencies can use our proposed index to estimate with a consistent methodology which properties are more exposed and with higher risk from fire damage so that specific fuel and vegetation management practices on and around them can be suggested or enforced.

Navigating the wildland-urban interface: Sensory pollution and infrastructure effects on mule deer behavior and connectivity

Climate and land-use change are modifying the availability of food and water resources, which is driving more wildlife to the wildland-urban interface. For many wildlife populations, use of these areas still requires habitat connectivity both within the interface and/or to wildland habitats. However, navigating these areas can be difficult due to human development and sensory pollutants, such as artificial night light. Determining how these components of urbanization influence the behaviors and functional connectivity of species is important for managing wildlife within these mixed-use landscapes. Here we used a movescape approach based on graph theory to characterize functional uses of the landscape using metrics for behavior, connectivity, and space use intensity. We found that mule deer (Odocoileus hemionus; n = 43) functional uses of anthropogenic landscapes in the Intermountain West, USA, were dependent not only on physical barriers, terrain, and sensory factors, but also the local levels of light exposure and vegetative greenness. Remotely sensed artificial light levels had a strong influence on how mule deer used the landscape by reducing the intensity of use in the most illuminated areas given forage availability. In contrast, relatively high local light levels were associated with increased use intensity within less developed areas—highlighting the foraging tradeoffs for species using the wildland-urban interface. Corridor use was reduced in areas where road and housing density were higher, and within-corridor movement was faster when artificial light was high and vegetative greenness was low. Developing a more mechanistic understanding of how species functionally use the landscape in relation to features of urbanization can enhance conservation by delineating areas important for connectivity and foraging, while providing insights into how future development and climate change may alter movement and behavior. Spatially-explicit estimates of functional uses can directly guide management decisions to maintain species resiliency and improve land-use planning.

Evaluating driving behavior patterns during wildfire evacuations in wildland-urban interface zones using connected vehicles data

Wildfire risk is increasing all over the world, particularly in the western United States and the communities in wildland-urban interface (WUI) areas are at the greatest risk of fire. Understanding the driving behavior of individuals to evacuate fire-affected WUI areas is important as the evacuees may encounter low visibility and difficult driving conditions due to burning material and steep topography. This study investigates the driving behavior patterns of individuals during historical wildfire events in rural and urban areas with mandatory evacuation orders using a connected vehicle dataset. This dataset provides the geolocation and timestamp of vehicles’ hard-braking (HB) and hard-acceleration (HA) events. The comparative analysis of the data demonstrated that the reported HA & HB event patterns were consistent in representing the varying driving behavior in response to the changing driving conditions and the depiction of the temporal and spatial impact of the fire in all studied areas. Moreover, the HB event dataset located critical traffic congestion points and the HA event dataset revealed the hurried response of evacuees on the exiting routes as a result of short-notice evacuation. In addition, significant differences in driving behavior patterns were noticed between rural and urban areas.

Edible fire buffers: Mitigation of wildfire with multifunctional landscapes.

Wildfires ravage lands in seasonally dry regions, imposing high costs on infrastructure maintenance and human habitation at the wildland-urban interface. Current fire mitigation approaches present upfront costs with uncertain long-term payoffs. We show that a new landscape intervention on human-managed wildlands-buffers of a low-flammability crop species such as banana irrigated using recycled water-can mitigate wildfires and produce food profitably. This new intervention can complement existing fire mitigation approaches. Recreating a recent, major fire in simulation, we find that a medium-sized (633 m) banana buffer decreases fireline intensity by 96%, similar to the combination of prescribed burns and mechanical thinning, and delays the fire by 316 min, enabling safer and more effective firefighting. We find that under climate change, despite worsened fires, banana buffers will still have a protective effect. We also find that banana buffers with average yield could produce a profit of $56k USD/hectare through fruit sales, in addition to fire mitigation.

A geographically flexible approach for mapping the Wildland-Urban Interface integrating fire activity data

The Wildland-Urban Interface (WUI) is the area where houses and natural vegetation meet or intermingle. WUI areas are exposed to an increased hazard of wildfires and have significantly expanded worldwide in the past few decades. In this study, we developed a new empirical approach for mapping the WUI by generating a WUI index based on the juxtaposition among buildings, vegetation, and the fire history of the study area. We first calculated the percentage coverage of buildings and three different fuel typologies within circular moving windows with radii of 100, 250, and 500 m, and then acquired the fire history data between 2012 and 2021 for Israel and the West Bank (Palestinian Authority) from the VIIRS active fires remote sensing product. We defined the WUI as cells where the combination of vegetation cover and building cover had more VIIRS fire detections than expected by chance. To assess the effects of using broad vs. local scale parameterizations on resulting WUI maps, we repeated this process twice, first using national-scale data, and then separately in four distinct geographic regions. We assessed the congruence in the amounts and patterns of WUI in regions as mapped by information from these two analysis scales. We found that the WUI in Israel and the West Bank ranged from 0.5% to 1.7%, depending on fuel type and moving window radius. The scale of parameterization (national vs. regional) affected the WUI patterns only in one of the regions, whose characteristics differed markedly than the rest of the country. Our new method differs from existing WUI mapping methods as it is empirical and geographically flexible. These two traits allow it to robustly map the WUI in other countries with different settlement, fuel, climate and wildfire characteristics.

Vegetation Analysis and Silvicultural Suggestions for Mitigating Fire Danger and Protecting Nature the Case of a Natura 2000 Site in Southern Greece

Purpose: The development of a methodological approach for the estimation of the wildfire danger in a protected area, located near a big city, based on the dominant factors contributing to a fire-prone environment and affect fire behavior. Theoretical framework: Vegetation management in protected areas characterized by sprawling of adjacent urban and suburban development patterns, is a complicated task, especially under Mediterranean climate due to the high vulnerability to wildfires. They should aim, among others, to mitigate forest-fire occurrence risk, eliminate the wildfire damages as well as to protect humans, and conserve the high biodiversity of the protected areas. Method: We generated a forest fire occurrence danger zone map based on: i) historical fire data ii) types of vegetation and forest ecosystem characteristics, iii) topographical characteristics, iv) distance from the settlements, and v) distance from the roads. A probability model equation for forest fire occurrence was produced. Wildland-Urban Interface mapping was also considered. Results and conclusion: Four categories of forest fire occurrence danger zones, ranging from very high to low, were classified. The zones with high and very high fire occurrence danger cover a low percentage of the study area (6.84% and 5.76%, respectively). In the very high fire danger zones, Pinus halepensis forest and evergreen sclerophyllous vegetation, prevail. A great part of the Wildland-Urban Interface WUI belongs to the zones of high and very high fire occurrence danger. Research implications: Several silvicultural and policy measures for creating fire-resilient ecosystems and mitigating the possibility of a wildfire occurrence and damages, are suggested. Originality/value: The determined site-specific vegetation management and policy measures are of great importance for land management in similar areas.

Experimental study of the large scale flammability of wood cladding at the wildland-urban interface

The aim of this work is to improve the understanding of the fire behaviour of building materials used in the wildland urban interface at a large scale. To this end, wood cladding was exposed to the heat flux from the burning of a cistus hedge ignited by a spreading fire front in a fuel bed of excelsior litter. Six experiments were performed with different configurations: hedge/cladding distance, cistus bulk density, hedge length. During the experiments, the assessment of the cladding ignition was observed by camera. Wind direction and velocity were measured continuously since the tests were conducted outdoors and wind is a significant driver of flame spread. Heat fluxes and temperatures were also measured in order to compare the intensity of the thermal aggression on the cladding coming from the burning hedge. When the distance between the hedge and the cladding was 3 m, the wood did not ignite even when the wind was in the direction of propagation towards the cladding. In these cases, the maximum heat flux was 18 kW m−2. This value did not allow the ignition of the wood cladding. When the distance was reduced, the ignition of the cladding depended on the wind direction. When the cladding was ignited, the heat fluxes from the burning hedge could exceed 100 kW m−2.

Pilot Study on Fire Effluent Condensate from Full Scale Residential Fires

AbstractStudies related to effluent produced by structure and vegetation fires often focus on gas phase or solid condensed phase, with limited treatment of liquid condensate generated as smoke cools to ambient. Recent post-fire human health concerns related to systemic human exposures to fire smoke and contamination of water distribution systems after wildland urban interface fires can be informed by understanding the chemical composition of liquid condensate resulting from large-scale fire experiments. In this pilot study, fire effluent (smoke) samples were continuously drawn from five different full-scale room-and-contents fire experiments, from which condensate was collected as the effluent cooled. Elevated concentrations of several volatile organic compounds (VOCs), including benzene, toluene, xylenes, styrene, naphthalene, and acetone along with several anions were detected in the acidic effluent. Many of these same VOCs have been identified in the air during firefighter safety experiments and in post-fire water distribution systems at levels that raise concern for human health. Benzene and naphthalene concentrations in the condensate were orders of magnitude above typical water quality standards and thus may directly contaminate large volumes of water. Peak benzene concentrations were similar to highest values reported from contaminated water distribution systems after wildfire events, though additional study is needed to understand the mechanisms by which this condensate may contribute to systemic contamination. Improved understanding of liquid condensate from fire effluent may be important to other areas of human and environmental health study, and some considerations are provided for future research.

Key elements of defensible space land use bylaw provisions in wildland-urban interface municipalities of Alberta, Canada

The province of Alberta, Canada has numerous municipalities partially or entirely within the wildland-urban interface, with anthropogenic and climactic factors increasing the level of susceptibility to wildland fires over the past century. Traditional fuel mitigation measures largely rely on landscape scale fuel management measures where treatments are often far removed from the buildings they are seeking to protect. Defensible space provisions within a municipality's land use bylaw can directly target vegetation treatments surrounding the buildings intended to be protected, and can be used alone or in conjunction with traditional landscape scale fuel management. This study investigates the use of defensible space land use bylaw provisions for increasing municipal resilience against wildland fires. The land use bylaws of 54 Alberta municipalities were examined for their inclusion of defensible space provisions. Despite a significant threat from wildland fires, many municipalities in Alberta were found to not have a defensible space provision within their land use bylaw. Key elements found to influence the strength of defensible space provisions include the operative word used, applicable structures/properties, and level of provision details. Rural municipalities were found to be more likely to have defensible space provisions, however they were generally weaker than those of urban municipalities.

Overview of the platform for experimentation and awareness-raising on fire risks at wildland urban interfaces (EXPLORII platform)

The aim of this article is to present a new experimental platform built by the University of Corsica in order to study the vulnerability of buildings to fires occurring at wildland urban interfaces. The platform is made up of a slope 10 m long by 6 m wide with an inclination of 20° and a flat surface located at its top hosting an instrumented single-storey house. The platform is equipped with different kinds of sensors: meteorological station, anemometers, load cell, heat flux gauges, thermocouples, cameras and smoke chemicals analysers. They allow obtaining experimental data on the burning of fuels and on the impact of fire on the buildings. Having a full-scale platform for studying fires at the wildland-urban interface (WUI) is important, particularly in terms of minimizing damage. By recreating realistic conditions and complex interactions between wildland fires, ornamental vegetation and residential areas, researchers can analyse and understand the mechanisms of fire spread in these vulnerable environments. In addition, a platform such as this enables testing and assessment of prevention and protection measures, such as fire-resistant building materials. Two experiments have been carried out to commission the platform with Douglas fir trees and test the experimental device. They have highlighted the protective effect of shutters, but also the role of double glazing as a thermal screen. The analysis of these first results has enabled improvements to be proposed to the experimental facility in order to better quantify the aerology and the heat fluxes impacting the building.

Wildland–Urban Interface: Definition and Physical Fire Risk Mitigation Measures, a Systematic Review

Due to the associated fire risk, the wildland–urban interface (WUI) has drawn the attention of researchers and managers from a range of backgrounds. From a land management point of view, it is important to identify the WUI to determine areas to prioritise for fire risk prevention. It is also important to know the fire risk mitigation measures available to select the most appropriate for each specific context. In this systematic review, definitions of the WUI were investigated and physical mitigation measures for reducing the risk of fire were examined from a land management perspective. The PRISMA 2020 Statement was applied to records published until 31 December 2022 and retrieved from the Web of Science, Scopus, and other research engines. A total of 162 publications from scientific journals and the grey literature were scrutinised and selected for analysis. Only publications providing an original definition of the WUI or proposing physical measures to reduce fire risk at the interface were retained, while those relating to emergency management and social perception were not considered. The risk of bias was reduced by internal cross-assessment by the research team. Definitions of the WUI (n = 40 publications) changed according to the research objective, varying broadly in identification of the anthropogenic and the wildland components of the interface. Terminology varied according to the definition, and the term wildland–human interface (WHI) was found to be more comprehensive than WUI. Methodological definitions of the interface ranged from using aggregated data through to identification of the buildings at risk in the interface with considerable precision. Five categories of physical fire risk mitigation measures (n = 128 publications) were identified: clearance distances, landscaping, wildland fuel management, land planning, and buildings design and materials. The most effective measures were those applied at early stages of urban development, and maintenance of assets and vegetation is crucial for preparedness. This review represents an analysis of scientific evidence on which land managers can base their actions to reduce the fire hazard risk in the WUI. The number of studies investigating the WUI is considerable, but experimental studies and quantitative results are scarce, and better communication and coordination among research groups and land management agencies is advisable. This systematic review was not registered.

Experimental demonstration test of damages in houses caused by wildland-urban interface fires

In Portugal, forest fuel management (FFM) around buildings is mandatory and regulated by Decree-Law. However, regarding the Portuguese Building Fire Safety Regulation, there are no specific provisions for applying safety measures to mitigate forest fire effects on buildings in the wildland-urban interface (WUI). Therefore, for evaluating the influence of not doing the mandatory FFM around houses in the WUI and, consequently, studying the forest fire exposure behaviour on typical housing construction systems, an experimental demonstration test (DT) was carried out in a small house in a WUI environment without FFM. The DT also aimed to understand if houses in the WUI using these construction systems could be a refuge during a forest fire. The construction systems and elements assembled were representative of materials used in Portugal and South Europe in recent years. In this DT, a land plot with forest fuels was burnt in Portugal. Firefront intensity, radiant heat flux on the house, temperatures, displacements of several construction elements, and damage sustained by construction systems during the test were recorded. The DT found that these construction systems could be vulnerable to forest fires, and the building may no longer be able to constitute a refuge during forest fire exposure.

Wildfire, evacuation, and cardiovascular events: A spatial exposure approach

Increasingly, adverse health effects from wildfire exposure are not limited to select populations in the wildland-urban interface. As wildfires continue to grow in frequency and intensity, they are also continuing to encroach on urban areas, putting larger and larger populations at risk. In this study we develop an innovative research design in the wildfire and health literature, and report results for a small scale implementation on California's central coast. Instead of focusing on smoke exposure and PM 2.5 or PM 10 as the primary physiological pathway linking wildfire and adverse cardiovascular health outcomes, we draw on a stress pathway as a potential link between stress and heart health. We use a novel spatiotemporal definition of wildfire exposure that is directly measurable at the individual level and acutely stressful: evacuation orders. Combining longitudinal health data from the dominant local hospital system in southern Santa Barbara County, California, we directly determine exposure to an evacuation order and smoke plumes from three large fires in the 2017–2019 wildfire period. Controlling for additional known risk factors, such as diabetes status and smoking status, we model the risk of secondary cardiovascular events (CVE) for 2411 patients with existing cardiovascular disease. Roughly 16.2% of patients (n = 391) were exposed to an evacuation order. We found evacuation order exposure was not significantly associated with an increased risk of cardiac events for the CVD population, but estimates hovered between 12.5 and 16.3% over un-evacuated cohorts. Smoke exposures were not significantly associated with CVE risk in models adjusted for evacuation orders nor unadjusted models, and estimates of effects varied widely. Both the method and the findings have implications for public health departments, clinicians and wildfire researchers.

Laboratory quantification of firebrand generation from WUI fuels for model development

Firebrands play a critical role in the propagation of wildland fires, particularly in the wildland-urban interface (WUI). The mechanism behind fire spread by firebrands is not well understood despite being responsible for a majority of structure losses during WUI fires. This study quantifies the generation of firebrands from three typical WUI fuels (Douglas fir, eucalyptus globulus, and coast live oak) inside a laboratory-scale wind tunnel, to provide necessary data to model the spread of wildland fires into and within communities by burning embers. A comprehensive set of test conditions were considered, including the initial fuel mass, fuel moisture content, mean twig diameter, and crosswind speed. Results showed that the firebrand yields for all three fuel species were independent of the total dry mass lost, but positively correlated with the crosswind speed and negatively correlated to fuel moisture content and mean twig diameter. Meanwhile, the firebrand yields by mass of the fuels under the same test conditions have the following order: coast live oak >Douglas fir >eucalyptus globulus. Scaling analysis was performed to organize the data under different test conditions, and unique firebrand yield correlations were then obtained for each fuel species. In addition, the masses and projected areas of the firebrands for each fuel species had a linear fitting correlation, and the slope of the fitting line was positively correlated to fuel moisture content but insensitive to crosswind speed and mean twig diameter. The data and correlations disclosed in this study could be vital for future simulations of fire spread in both the wildland and WUI.

Effect of wind turbulences on the burning of a rockrose hedge

With climate change, complex fire scenarios at Wildland Urban Interfaces (WUI) have become a growing concern for authorities worldwide. Such scenarios involve unfavorable wind conditions, which greatly increase the fire spread near communities and makes the intervention of firefighters even more complex. To design effective fire safety regulations to protect communities, it is important to have a clear understanding of the role of wind in the burning of vegetation to help identify the vectors of fire spread within the defensible zone. In this context, this paper attempts to relate the properties of the flames generated by the burning of a reconstructed rockrose hedge to the atmospheric wind turbulence using four field-scale experiments. The experimental setup includes 3 visible cameras to record the flame geometry, extracted by post-processing; 3 pairs of radiant and total heat fluxes to record the heat fluxes downstream of the hedge, and an anemometer to measure the wind speed and direction. The results show that the wind at the experimental site is composed of wall-bounded turbulent structures coupled with strong and short intermittent events such as gusts. Regarding the fire, the four replicates show similarities in phase durations and dynamics, but revealed dependencies on Reynolds number and turbulent kinetic energy when averaging over the fully developed flame phase. In addition, a slight flapping motion of the ensemble flame was observed and associated with wave numbers of the order of the turbulent cascade in the kinetic energy power spectra. Finally, the analysis of wind and fire intermittencies revealed that strong and short wind events generate large fluctuations of flame geometry and received heat fluxes that increase with the characteristic time of the event considered.

Fire in the Wildland-Urban Interface: Selecting Firewise Shrubs to Reduce Wildfire Risk

Properties in the wildland-urban interface frequently use shrubs in landscaping. Although shrubs are attractive, some types can be risky to plant near structures in fire-prone areas. Property owners in such areas should consult existing guides for shrubs that do not burn easily and should routinely maintain shrubs and other vegetation within the defensible space around houses and other structures.

Evacuation Simulation under Threat of Wildfire—An Overview of Research, Development, and Knowledge Gaps

Wildfires have become a common incident over the past decades, and they have been threatening people’s lives and assets. In the communities close to wildlands or wildland–urban interfaces (WUI), these threats become increasingly serious, and in case of wildfires, people are advised or often have to evacuate the area to save their lives. In order to have a safe and effective evacuation, data on people’s behavior and decisions during wildfires, evacuation modeling, and traffic simulations are required. This paper reviews past and recent research on evacuation, human behavior in wildfires, evacuation modeling, and traffic simulation. Similar research on evacuation in other situations is also reviewed, and the applicability of the models and simulations on wildfires is discussed. Different stages for an evacuation modeling design are assessed, and the gaps and challenges in obtaining an effective evacuation model are presented.

Fires at the wildland-industrial interface. Is there an emerging problem?

Over the past years, wildfires have raged with unprecedented intensity across the world, becoming a growing problem, as weather conditions conductive to wildfire ignition and spread will increase in frequency and severity worldwide. This, coupled with a growing human expansion, leads to an increase in wildfire risk and in the threat to wildland-urban interface (WUI) communities. Commonly, definitions for WUI areas consider homes, commercial facilities, office and public buildings. This excludes industrial installations, where wildfires can trigger accidents or cascading events leading to extremely dangerous situations for the population causing enormous economic losses. In this paper, the problem associated to the wildland-industrial interface (WII) is analyzed. A methodology to obtain a global WII map is described, and the first WII maps for Europe and Asia are provided. Results show that, in Europe, 2.5% of the land and 6% of vegetated areas are WII, while in Asia these are respectively 0.24% and 0.5%. An analysis of how wildfire triggered industrial accidents can be considered when performing quantitative risk assessments (QRA) in industrial sites is also performed, identifying the current state of the art and research gaps, with the aim of helping industry, public authorities and policy makers, for better accident prevention, preparedness and response.

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.