Maps of California's Wildland Urban Interface (WUI) generated using the Time Step Moving Window (TSMW) method outlined in the paper "Remapping California's Wildland Urban Interface: A Property-Level Time-Space Framework, 2000-2020".

Please cite the original paper:

Berg, Aleksander K, Dylan S. Connor, Peter Kedron, and Amy E. Frazier. 2024. “Remapping California’s Wildland Urban Interface: A Property-Level Time-Space Framework, 2000–2020.” Applied Geography 167 (June): 103271. https://doi.org/10.1016/j.apgeog.2024.103271.

WUI maps were generated using Zillow ZTRAX parcel level attributes joined with FEMA USA Structures building footprints and the National Land Cover Database (NLCD).

All files are geotiff rasters with WUI areas mapped at a ~30m resolution. A raster value of null indicates not WUI, raster value of 1 indicates intermix WUI, and a raster value of 2 indicates interface WUI.

Three WUI maps were generated using structures built on of before the years indicated below:

2000 - "CA_WUI_2000.tif"

2010 - "CA_WUI_2010.tif"

2020 - "CA_WUI_2020.tif"

Acknowledgments -

We thank our reviewers and editors for helping us to improve the manuscript. We gratefully acknowledge access to the Zillow Transaction and Assessment Dataset (ZTRAX) through a data use agreement between the University of Colorado Boulder, Arizona State University, and Zillow Group, Inc. More information on accessing the data can be found at http://www.zillow.com/ztrax. The results and opinions are those of the author(s) and do not reflect the position of Zillow Group. Support by Zillow Group Inc. is acknowledged. We thank Johannes Uhl and Stefan Leyk for their great work in preparing the original dataset. For feedback and comments, we also thank Billie Lee Turner II, Sharmistha Bagchi-Sen, and participants at the 2022 Global Conference on Economic Geography, the 2022 Young Economic Geographers Network meeting, and the 2023 annual meeting of the American Association of Geographers. Funding for our work has been provided by Arizona State University's Institute of Social Science Research (ISSR) Seed Grant Initiative. Additional funding was provided through the Humans, Disasters, and the Built Environment program of the National Science Foundation, Award Number 1924670 to the University of Colorado Boulder, the Institute of Behavioral Science, Earth Lab, the Cooperative Institute for Research in Environmental Sciences, the Grand Challenge Initiative and the Innovative Seed Grant program at the University of Colorado Boulder as well as the Eunice Kennedy Shriver National Institute of Child Health & Human Development of the National Institutes of Health under Award Numbers R21 HD098717 01A1 and P2CHD066613.

A map with various base layers to be used as a template for creating thematic maps for the Napa County CWPP online maps. Most layers are from Napa County's online gis data catalog but some layers were derived from public data sources such as Wikipedia and others.This map highlights WUI areas as defined by CAL FIRE in their WUI 12_3 layer. Description below:This dataset adds housing density class (DEN4) and wildfire hazard (FHSZ) attributes to WUI12_2 - FRAP’s preliminary result in an effort to capture Wildland Urban Interface (WUI) for the 2015 Assessment. The current dataset is appropriate for displaying the overall pattern of WUI development at the county level, and comparing counties in terms of development patterns. Until the dataset is refined through a field review process, it is not suited for WUI designations for individual houses or neighborhoods.

Three WUI classes are mapped: 1) Wildland Urban Interface – dense housing adjacent to vegetation that can burn in a wildfire, 2) Wildland Urban Intermix - housing development interspersed in an area dominated by wildland vegetation subject to wildfire, and 3) Wildfire Influence Zone - wildfire susceptible vegetation up to 1.5 miles from Wildland Urban Interface or Wildland Urban Intermix.

Housing Density (DEN4) 1) Less than one house per 20 acres 2) One house per 20 acres to one house per 5 acres 3) More than one house per 5 acres to 1 house per acre 4) More than 1 house per acre

Fire Hazard Severity Zone (HAZ_NUM: 1=Moderate, 2=High, 3=Very High) Source: State Resposibility Areas (fhszs06_3), Local Responsibility Areas (fhszl11_1)

Due to the mixed distribution of buildings and vegetation, wildland-urban interface (WUI) areas are characterized by complex fuel distributions and geographical environments. The behavior of wildfires occurring in the WUI often leads to severe hazards and significant damage to man-made structures. Therefore, WUI areas warrant more attention during the wildfire season. Due to the ever-changing dynamic nature of California’s population and housing, the update frequency and resolution of WUI maps that are currently used can no longer meet the needs and challenges of wildfire management and resource allocation for suppression and mitigation efforts. Recent developments in remote sensing technology and data analysis algorithms pose new opportunities for improving WUI mapping methods. WUI areas in California were directly mapped using building footprints extracted from remote sensing data by Microsoft along with the fuel vegetation cover from the LANDFIRE dataset in this study. To accommodate...

The current dataset is appropriate for displaying the overall pattern of WUI development at the county level, and comparing counties in terms of development patterns. Until the dataset is refined through a field review and quality assurance process, it is not suited for WUI designations for individual houses or neighborhoods.The data can be downloaded as a file geodatabase here: GIS Mapping and Data Analytics | CAL FIREThree WUI classes are mapped:Wildland Urban Interface – dense housing adjacent to vegetation that can burn in a wildfire,Wildland Urban Intermix - housing development interspersed in an area dominated by wildland vegetation subject to wildfire, and Wildfire Influence Zone - wildfire susceptible vegetation up to 1.5 miles from Wildland Urban Interface or Wildland Urban Intermix. Wildland Urban Interface, Wildland Urban Intermix, and Wildfire Influence Zones. The model uses residential structure density and vegetative cover to define areas within the Fire Hazard Severity Zones. Primary Data Inputs:Fire Hazard Severity Zones (FHSZ_Assessment25_1)Housing Unit Density (HousingUnit_Density2020_DEN4)Secondary Data Inputs:(used to determine vegetation dominance)State Wildland Zones (FHSZ_State_Wildland_Zones_v17_1)Canopy Cover (CanopyCoverSALO2020)Fire Hazard Severity Zones: This source raster dataset represents Fire Management Analysis Zones as adopted officially on April 1, 2024 for State Responsibility Area (SRA) and as distributed to local governments in February and March of 2025 for Local Responsibility Areas (LRA). The source data for the LRA release also contains FHSZ coverage for Federal Responsibility Areas, but these data are used to fill out the state for assessment purposes only. Data sources: FHSZALL_v25_1 (SRA Approved and LRA Recommended) Statewide_v17_4 (Federal Responsibility Areas)Housing unit density classes for California derived from 30-m rasters extracted from Wildfire Risk to Communities: Spatial datasets of wildfire risk for populated areas in the United States and reprojected to California Teale Albers NAD87. DEN4 Description Less than 1 Housing Unit per 20 acres1 Housing Unit per 20 acres to 1 Housing Unit per 5 acresMore than 1 Housing Unit per 5 acres to 1 Housing Unit per acre More than 1 Housing Unit per acre After classifying, clusters of DEN4 values less than 80 cells (just under 18 acres) were nibbled to the nearest adjacent DEN4 class.State Wildland Zones and Canopy Cover: State Wildland Zones are used to determine the dominance of vegetation. Areas which would otherwise be classed as Wildland Urban Interface.area reclassed to Intermix if the vegetation cover is 50% or more. These canopy cover data are used in concert with SALO Canopy Cover to determine vegetation dominance in areas both within and outside of the the extent of the wildland zones.State Wildland Zones: State wildland zones are determined by the attribute flame class, which was derived as part of fire hazard modeling used in the determination of Fire Hazard Severity Zones and represent areas where wildland fire behavior can be assessed using common fire behavior tools. It is derived from fuel model attributes slope, and local fire weather conditions as processed through the NEXUS Fire Behavior platform, and reflects flame front characterization of intensity (flame length) that was then aggregated to fire environment polygons, averaged across the polygon area, and finally classified nominally according to quantile distributions with some threshold adjustments to reflect realistic class breaks for marginal areas of widely accepted hazard levels. All wildland zones are 50% or more vegetated.Canopy Cover: The horizontal cover fraction occupied by tree canopies. 2020 SALO Canopy cover data was downloaded for all California counties from here: https://forestobservatory.com/ on 5/17/2022 and mosaiced into one statewide dataset, reprojected from UTM 10 to Teale Albers NAD83 and resampled to 30m. Note: Vegetation dominance is determined as either FHSZ Wildland Zone 1-3 or SALO > 50% cover. A 3X3 cell circular focal mean is applied and areas with 0.5 or greater are considered at least 50% vegetated.-----------------------------------------------------------------These data are analyzed according to the following parameters:Interface:DEN4 Class 3 or 4 In Moderate, High, or Very High Fire Hazard Severity ZoneLess than 50% vegetation coverSpatially contiguous groups of 30m cells that are approximately 20 acres in size or largerIntermix:DEN4 Class 2 or 3In Moderate, High or Very High Fire Hazard Severity ZoneReclassed Interface:Interface cell groups less than 20 acresInterface that is 50% or more vegetated and in spatially contiguous groups of 30m cells that are at least 20 acres in size Intermix is spatially contiguous groups of 30m cells approximately 100 acres in size or largerInterface and Intermix are then combined. After combining, any cell group with fewer than 80 cells is classed to the value of its neighbor.Influence Zone:Up to 1.5 miles from Interface or IntermixIn Moderate, High, or Very High Fire Hazard Severity ZoneNot Interface or IntermixInterface, Intermix and Influence Zones are then combined. After combining, any cell group with fewer than 80 cells is classed to the value of its neighbor.A final step in the model addressed an inadvertent error invoked by the processing of potential interface conversion to Intermix for small fragments (<20 acres of Interface) and larger areas of Interface that were covered by a majority (>50%) vegetation within the areas otherwise defined as Interface because of meeting housing unit density and hazard requirements. When these lands were then subject to the final size minimum of 100 acres they then reverted to being potential buffer areas. This was remedied by selecting all lands that met the criteria of DEN4 values 3 and 4 (i.e.,all areas with housing density greater than 1 HU/ac) and reverting them to Interface designation. These previously eliminated but now reverted Intermix areas did not meet the 100 acre requirement and did not produce additional buffer zone influence areas from them. In most cases they are sufficiently embedded within Influence Zone buffers to be consistent with map objectives describing the land in terms of exposure and opportunity for community protection and risk mitigation.

Vegetation treatment at the landscape scale is focused on reducing the likelihood of a ground fire increasing in intensity and helping suppression forces more easily contain a fire. This is accomplished by modifying fire behavior through strategic removal or modification of vegetation (Finney and Cohen 2003, Graham et al. 2004). Certain wind and weather conditions lead to ultrahigh-intensity, fast-moving, wind-driven wildfires. Although the most individually destructive, these extreme fires represent a small number of the total fires that occur each year. While vegetation treatments under the CalVTP may not be able to slow or halt such extreme fires, most fires that occur within the state are not highly wind driven and the proposed vegetation treatments can help slow and suppress them. Vegetation treatments can also play a valuable role in containing the more extreme fires, when weather conditions shift, wind subsides, and fire intensity decreases. By implementing the modeled Fuel Break Treatment Areas, the CalVTP would strategically modify portions of this landscape to reduce losses from and improve resiliency to wildfire.

WILDLAND URBAN INTERFACE Wildland Urban Interface (WUI) Treatment Area was derived from WUI12_2 (CAL FIRE FRAP) and SRA18_2 (CAL FIRE FRAP). WUI was identified and extracted from WUI12_2. SRA was identified and extracted from SRA18_2. WUI and SRA were then overlaid with each other and areas of overlap create the WUI fuel reduction treatment area for the CalVTP.

The methodology for the original creation of WUI03_1 follows below. The mythology for WUI03_1 and WUI12_2 is foundationally the same, but WUI12_2 utilizes updated and more precise datasets to further refine the modeled wildland urban interface.

Spatial Modeling for WUIIn 2001 CAL FIRE FRAP, in conjunction with the California Fire Alliance, undertook the task of spatially modeling the Wildland-Urban Interface (WUI). The modeling process combines three main factors: fire threat, human asset exposure, and proximity.

Using these three building blocks, maps were developed that defined a WUI footprint and contained specific information that supports the development of strategies to prioritize mitigation efforts to achieve efficient results. All three components contribute to a risk assessment of potential loss from wildfire. The larger the hazard, the more assets exposed, and the closer these components are to one another, the higher the risk of loss.

Wildland Fire Hazards Wildland fire hazards is a combination of defining the fuel hazard and identifying the probability of burning.

Defining the Fuel Hazard

CAL FIRE FRAP began the process of modeling the WUI fuel reduction treatment area by defining the fuel hazard. This was achieved by first developing a comprehensive fuel type map consisting of fuel composition and structure information. The comprehensive fuel type map was then joined to the Fire Behavior Prediction System (FBPS) fuel models, a similar method to the one utilized in the Sierra Nevada Ecosystem Project. Recent large fires were then captured in the data with appropriate burn and growth models applied. This information was converted to a fire hazard map by calculating the expected fire behavior for unique combination of slope and fuels under average bad fire weather conditions. Each fuel-by-slope-class combination received a surface hazard rank.

A final fuel hazard product was created by gridding the state into approximately 450-acre squares and assigning a hazard rank to each grid cell based on its slope class, fuel model, and the presence of ladder and crown fuels. The assigned values consisted of Very High, High, and Moderate.

Probability of Burning The probability of fire burning in a given location is based on a variety of factors including vegetative fuel condition, weather, ignition sources, fire suppression response (FRAP 2003). Through the utilization of 47 years of fire history, fire perimeters, and the comprehensive fuel type map described above, an annual likelihood that a large damaging fire would occur in a particular fuel type was developed. This probability matrix is referred to as Probability of Burning (“PFIRE”), where:

Very High is the probability of fire 1 percent per year or greater, High is the probability of fire 0.33 percent - 1 percent per year, and Moderate is the probability of fire is less than 0.33 percent per year.

These values relate to fire frequency equivalents of less than 100 years, 100-300 years, and greater than 300 years, respectively.

Assesing Fire Threat

The fire threat is derived by combining Fuel Hazard (“Hazard Rank”) and PFIRE, which determines areas of high, moderate, and low fire threat. The creation of the fire threat in the modeling process is an important building block when identifying the WUI fuel reduction treatment area geospatially.

Fire Threat Matrix (PFIRE and Hazard Rank)

Human Asset Exposure Human asset exposure was defined by identifying categories in the interface:

Urban – 1+ house per ½ acre, Intermix – 1 house per ½ acre to 1 house per 5 acres, Rural – 1+ house per 5 acres to 1 house per 40 acres, and Wildland – less than 1 house per 40 acres.

Census block data was used to determine the number of structures per acre. Census blocks are typically designed to represent 400 people, leading to wide variation in block size. Census blocks do not distinguish restricted development areas (federal lands), from unrestricted developed areas (private lands). Therefore, to accurately capture housing densities, FRAP spatially redistributed the populations off restricted development lands. All federal lands were considered restricted development lands for the analysis. For example, if a census block had 400 people over 20 acres, but 10 of those acres were restricted development lands, the population would be adjusted from 20 houses per acre up to 40 houses per acre for unrestricted lands.

The identification of interface categories creates a measure of human asset exposure, completing another building block of defining the WUI fuel reduction treatment area geospatially.

Proximity Proximity can be described as areas where human assets and the vicinity of a fire threat intersect. Vicinity is defined, in accordance with 2001 California Fire Alliance research, as all areas within 1.5 miles of a fire threat. The 1.5-mile distance is the approximate distance embers and flaming material (firebrands) can be carried from a wildland fire to the roof or other part of a structure. All Intermix and Rural areas (established via the human asset exposure modeling described on the previous page) within 1.5 miles of a fire threat (established via the wildfire hazard modeling described above) were labeled with the highest threat rank, while urban areas were labeled with the highest threat rank if they were within 0.25-mile of a fire threat. This includes more urban, developed areas in close proximity to wildland areas in the defined WUI, while excluding the urbanized areas in the central parts of cities. By identifying the proximity of human assets to a fire threat, a geospatial representation of the WUI fuel reduction treatment area emerges.

Two zones also emerge within the model: the defense zone and the threat zone. These two zones are sometimes referred to as the WUI Zone of Influence. The defense zone is the immediate 0.25-mile distance extending from the urbanized area, while the threat zone is the 1.25-mile further extending from that 0.25-mile buffer towards the wildlands. These zones of influence represent the proximal lands where different types of treatments would likely influence risk to people, property, and other infrastructure. These zones can assist in the prioritization of subsequent activities.

For more information, access the California Vegetation Treatment Program PEIR (Cal VTP). This is a hosted tile layer with an associated tile layer package. This data represents modeled wildland urban interface areas within treatable areas to be used in the CalVTP PEIR. The data is viewed in the "California State VTP EIR Treatable Areas - Web Map" which feeds into the "California Vegetation Treatment Program PEIR - Web App".

This data layer will be needed for as long as the web map and web application are live.

This dataset was created to better understand the devastating Eaton Fire of January 2025. The fire contaminated a large area across Altadena, Pasadena, and Sierra Madre California with hazardous ash and soot. To improve both the response and recovery to this event, members of the NASA Jet Propulsion Laboratory, California Institute of Technology, the University of California, Los Angeles, and the California Institute of Technology collected and analyzed ash samples taken in and near the Eaton Fire burn scar.

This dataset includes handheld spectroscopy measurements for 87 ash samples as well as their metadata. Additional maps, metadata, and code examples are available on Zenodo: https://doi.org/10.5281/zenodo.16538735

This is the Variable Constrained Areas (VCAs) in the SCAG Region developed for Connect SoCal, the 2020-2045 Regional Transportation Plan/Sustainable Communities Strategy (RTP/SCS). VCAs include Wildland-Urban Interface, Grazing Lands and Farmlands, 500 Year Flood Plains, CalFire Very High Severity Fire Risk, Natural Lands and Habitat Corridors..Wildland-Urban Interface (WUI) – Data on areas where housing and vegetation intermingle (“intermix WUI”) and areas with housing in the vicinity of contiguous wildland vegetation (“interface WUI”) were derived from the 2010 national Wildland-Urban Interface dataset developed by the SILVIS Lab at the University of Wisconsin-Madison;Grazing Lands and Farmlands within Incorporated Jurisdictions – Similar to farmlands identified in unincorporated areas, grazing lands and farmland information within incorporated areas were identified through the Farmland Mapping & Monitoring Program (FMMP) in the Division of Land Resource Protection in the California Department of Conservation, which underwent review by local jurisdictions;500 Year Flood Plains – Information on flood areas were derived from the Digital Flood Insurance Rate Map (DFIRM), obtained from Federal Emergency Management Agency (FEMA) in August 2017. The DFIRM Database is a digital version of the FEMA Flood Insurance Rate Maps (FIRM) that is designed for use with digital mapping and analysis software. The FIRM is created by FEMA for the purpose of floodplain management, mitigation, and insurance activities for the National Flood Insurance Program (NFIP), and was included for local jurisdiction review through SCAG’s Bottom-Up Local Input and Envisioning Process;CalFire Very High Severity Fire Risk (state and local) – Information on areas with very high fire hazards was derived from CalFire’s state responsibility area and local responsibility area Very High Fire Hazard Severity Zone (VHFHSZ) data, accessed by SCAG in early 2019; andNatural Lands and Habitat Corridors – Data on habitat corridors was derived from California Essential Habitat Connectivity Project, as developed by the California Department of Fish and Wildlife, which identifies large blocks of intact habitat or natural landscapes with connectivity corridors essential for local wildlife. This dataset benefits from feedback from a selection of federal, state, local, tribal, and non-governmental organizations throughout California, and was made publicly available in 2010.PLEASE NOTE this data is intended for planning purposes only, and SCAG shall incur no responsibility or liability as to the completeness, currentness, or accuracy of this information. SCAG assumes no responsibility arising from use of this information by individuals, businesses, or other public entities. The information is provided with no warranty of any kind, expressed or implied, including but not limited to the implied warranties of merchantability and fitness for a particular purpose.

The CalVTP, developed by the Board of Forestry and Fire Protection (Board), is a critical component of the state’s multi-faceted strategy to address California’s wildfire crisis. The CalVTP defines the vegetation treatment activities and associated environmental protections to reduce the risk of loss of lives and property, reduce fire suppression costs, restore ecosystems, and protect natural resources as well as other assets at risk from wildfire. The CalVTP supports the use of prescribed burning, mechanical treatments, hand crews, herbicides, and prescribed herbivory as tools to reduce hazardous vegetation around communities in the Wildland-Urban Interface (WUI), to construct fuel breaks, and to restore healthy ecological fire regimes. The California Department of Forestry and Fire Protection (CAL FIRE) has the primary responsibility for implementing proposed CalVTP vegetation treatments, though many local, regional, and state agencies could also employ the CalVTP to implement vegetation treatments if their projects are within the scope of the CalVTP (see Final PEIR, Chapter 2, Program Description). The CalVTP will allow CAL FIRE, along with other agency partners, to expand their vegetation treatment activities to treat up to approximately 250,000 acres per year, contributing to the target of 500,000 annual acres of treatment on non-federal lands as expressed in Executive Order (EO) B-52-18.

This feature service contains proposed projects under the California Vegetation Treatment Program (CalVTP). This is to facilitate an open process for evaluating projects.The (CalVTP), developed by the Board of Forestry and Fire Protection (Board), is a critical component of the state’s multi-faceted strategy to address California’s wildfire crisis. The CalVTP defines the vegetation treatment activities and associated environmental protections to reduce the risk of loss of lives and property, reduce fire suppression costs, restore ecosystems, and protect natural resources as well as other assets at risk from wildfire. The CalVTP supports the use of prescribed burning, mechanical treatments, hand crews, herbicides, and prescribed herbivory as tools to reduce hazardous vegetation around communities in the Wildland-Urban Interface (WUI), to construct fuel breaks, and to restore healthy ecological fire regimes. The California Department of Forestry and Fire Protection (CAL FIRE) has the primary responsibility for implementing proposed CalVTP vegetation treatments, though many local, regional, and state agencies could also employ the CalVTP to implement vegetation treatments if their projects are within the scope of the CalVTP (see Final PEIR, Chapter 2, Program Description). The CalVTP will allow CAL FIRE, along with other agency partners, to expand their vegetation treatment activities to treat up to approximately 250,000 acres per year, contributing to the target of 500,000 annual acres of treatment on non-federal lands as expressed in Executive Order (EO) B-52-18. For more information, visit the CalVTP Homepage and Storymap.

Author: Angela Scanlon

Author email: opendata@ottawa.ca

Maintainer Organization: Innovative Client Services Dept.

Date created: May 27th, 2022

Update frequency: As needed.

Attributes:

NAME PHASE STATUS ADDRESS CITY