The information in this section apples to both the spatial and GeoEnrichment modules.
STATE
A two-character state abbreviation is assigned to every polygon, based on the state that contains the majority of the polygon's area. Polygons conform to the landscape and fire behavior parameters, and are continuous across the landscape.
WRE_ID
A unique identifier for each polygon in the dataset.
WRE_CLS
A polygon's geometry type:
| Value | Description | Details |
| A | Adjacent | Interface polygons in closest proximity to the natural fuel bed. Risk assigned to these areas is based on direct flame impingement or the intensity of ember cast threat from the adjacent fuel bed. Fire impacts within an adjacent zone include flame impingement, high density of ember case, urban conflagration, and difficulties associated with evacuation. |
| C | Urban conflagration | Interface polygons beyond adjacent. These areas are no longer within range of embers and flame impingement. They are only susceptible to urban conflagration (fires burning structures as fuel) and potential evacuation difficulties. |
| H | Water bodies | Polygons representing areas of surface water larger than 10 acres |
| L | Potential fuel islands inside interface | Polygons that have been programmatically identified as fuel islands, but have not been examined visually |
| U | Urban areas | Polygons representing areas of high structure density (interface), with minimal likely exposure to wildfire |
| V | Fuel islands inside interface | Polygons designated as fuel beds (similar to wildland), but surrounded by a high density of structures (interface) which have been vetted manually. Fuel islands of this type have been vetted by visual examination to confirm the presence of fuel. |
| W | Wildland | Polygons with the lowest structural density. Fuel dominates these areas, with little interruption by infrastructure, such as structures or paved surfaces. Fire moves through these areas relatively unimpeded. |
| X | Intermix | Polygons with moderate structure density. These areas contain a mix of built environment and natural/planted fuels. Surface fires can burn easily through these areas, but will be influenced by structures and paved surfaces. |
WRE_MODEL
A designation of model type only. This field specifies the risk type applied to each polygon in assessing its wildfire risk.
RISKDESC
Descriptive risk class based on the overall 0-to-75 risk rating (RISK_LEVEL) assigned to a polygon. RISK_LEVEL is described as follows:
| RISKDESC Value | Associated RISK_LEVEL Range |
| Minimal Likely Exposure (MLE) | 0 |
| Low | 1-9 |
| Moderate | 10-23 |
| High | 24-35 |
| Very High | 36-50 |
| Extreme | > 50 |
This classification scheme is applied to all wildland and intermix polygons, and to all fuel islands and adjacent zones in interface areas. Polygons designated as either surface water or urban areas outside adjacent or urban conflagration zones have been found to have minimal wildfire risk and therefore receive a classification of Minimal.
RISK_LEVEL
Overall wildfire risk rating for a polygon, on a 0-to-75 scale, with 0 being the lowest possible risk and 50 the greatest. This is the most granular overall wildfire risk rating. It is derived from the contribution of all other outputs, weighted according to the polygon's risk type (interface, intermix, or wildland), and its location in a general region of the country. By convention, all polygons designated as peripheral zones have a RISK_LEVEL of 1 and all polygons designated as MLE or surface water have a RISK_LEVEL rating of 0.
Composite ratings
The six fields in this subsection represent a composite, weighted rating for each group of individual outputs. The weight of their contributing factors varies by polygon, model type (interface, intermix, or wildland), and the polygon's location within a general region of the country. Composite ratings for polygons designated as urban MLE or surface water and their individual outputs are always 0.
The SEVERITY rating is a weighted composite composed of fireline intensity (INTENSITY), crown fire (CROWN_FIRE), wind speed (WIND_SPD), and ember cast (EMBER_CAST). The combination of these elements is an estimation of the impact of a wildfire, should one occur in that location. This rating behaves as if a wildfire was burning everywhere on the landscape. Since such a scenario is not realistic, wildfire frequency must also be considered in the overall rating.
FREQUENCY
The FREQUENCY rating consists of FSim burn probability (BURN_PROB), historic fire perimeter (HIST_PERIM), probability of ignition (PROB_IGNIT), and distance to the nearest electrical transmission line (LINE_DIST). Frequency refers to the likelihood of a fire occurring in a location and, when combined with severity, comprises most of the overall risk rating, in terms of weight.
COMMUNITY
The COMMUNITY rating includes factors that relate to structures and the conditions that immediately surround them. These are structure density and the distance to the nearest structure (see STRUCTURE, below), wind-aligned roads (W_ALIGN_RD), access/egress (ACC_EGRESS), and vegetation cover (VEG_COVER).
DAMAGE
The damage rating refers to two factors that indicate the presence of insect and disease damage to trees (I_AND_D) and past wildfire damage to structures/historic loss (HIST_LOSS). Both of these factors can indicate a tendency toward structure risk in the future.
MITIGATION
The mitigation rating consists of factors that could reduce an area's wildfire risk. The components of this composite are distance to the nearest fire station (F_STN_DIST), distance to the nearest draft/dip water source (WATER_DIST), a topographic position index (TOPO_POS), and the amount of burnable fuel (BURNABLE). Even though these elements potentially limit the risk due to wildfire, they are still expressed as lower numbers to indicate mitigating effect and higher numbers to indicate the absence of that effect. Doing so maintains a consistent polarity across the entire model, so that low numbers are always associated with less risk.
URBAN CONFLAGRATION
This rating refers to areas that are subject to fire that burns using structures for fuel. Areas throughout the interface zone are rated for both Structure Threat (STR_THREAT) and House to House threat (H2H_THREAT), but areas beyond the ember cast/flame impingement zone, though not so far away as to be considered Urban Likely Minimum Exposure (MLE) are considered to be urban conflagration-only zones.
Severity outputs
INTENSITY (fireline intensity)
An output of fire behavior modeling indicating the predicted heat produced by a fire, if one were to burn through an area. Higher values indicate greater damage potential to structures.
CROWN_FIRE
A measure of the areal percentage of predicted crown fire within 0.5 miles of the area.
WIND_SPD (wind speed)
A measure of the effect of wind speed at the 99th percentile in the area, based on data provided by the National Oceanographic and Atmospheric Administration (NOAA). Areas of high relative humidity have a reduction factor associated with them because, while the absolute wind speed may be high, the threat associated with this wind is lower than in areas that are drier and therefore more fire prone.
EMBER_CAST
An indicator of the amount of ember cast that would be experienced from surrounding areas. Ember cast is derived using the maximum spotting distance based on fire behavior calculations, using fuel, weather, and topographic inputs. Areas surrounded by many cells that are casting embers at great distances will have the highest values. The value is an aggregate measure of all ember-casting locations within the maximum spotting distance of the area.
Frequency outputs
BURN_PROB (burn probability)
This factor is base don a dataset produced by the Large Fire Simulator at the US Forest Service's Rocky Mountain Research Station5. It is an estimation of the likelihood of fire based on patterns of fuel, historic weather, and past fires. It uses an approach that models large numbers of simulated fires and records how often different locations are burned. Greater numbers of fires burning a landscape indicate that it is more prone to future fires.
HIST_PERIM (historic fire perimeters)
Regions that have historically had wildfires are likely to experience them in the future. This factor is produced by mapping GEOMAC (now NIFC) wildfires greater than 100 acres since 2000.
PROB_IGNIT (probability of ignition)
This factor refers to how likely an ember is to find a receptive fuel bed. Reflected in this calculation are fuel moisture, elevation, shading, and aspect of every independent 30-meter pixel.
LINE_DIST (distance to nearest transmission line)
Transmission lines continue to be potential sources of igniting wildfires. This factor assigns higher point values to locations closer to transmission lines (up to 1 mile away).
Community outputs
STRUCTURE
The more structures there are in a given area, the greater the risk of structure loss due to wildfire. In intermix areas, structural density is evaluated as an indicator of increased risk. In interface areas, however, the shape and configuration of smaller parcels can affect the susceptibility of structures to being burned by each other. Because of this difference in fire dynamics, distance to nearest neighboring structure, rather than structure density, is used in interface polygons. The principle is the same, however, in both situations – more structures equates to greater wildfire risk.
W_ALIGN_RD (wind aligned roads)
Roads aligned with predominant wind direction in high structure density areas can produce a channeling effect that can carry embers and fan flames along such corridors. Areas where roads are more orthogonal to wind direction are much less susceptible to this effect.
ACC_EGRESS (access/egress)
The number and type of roads providing access to and from an area, along with the number of houses in an area can be used to estimate the potential difficulty of evacuating residents and moving suppression resources into the area. Wildfire Risk Extreme rates this difficulty based on the number of houses in an area and the distance to the nearest road large enough to act as a primary evacuation route.
VEG_COVER (vegetation cover)
Vegetation cover refers to the amount of vegetation (tree, grass, or shrub) that occurs in wildland and intermix areas. Although canopy cover is an obvious input to fire behavior, this dataset provides a finer-scale assessment of fuel potential across all vegetation types.
Damage outputs
I_AND_D (insects and disease)
Forests are subject to certain kinds of pest outbreaks that can influence fire behavior. Insect and disease data from the US Forest Service are used to increase risk ratings where damage is present.
HIST_LOSS (historic loss)
The US Forest Service6 aggregates structure loss information at the fire incident level. This loss data is used similarly to historic fire perimeter data, in order to assign additional risk in the overall rating at a regional scale.
Mitigation outputs
F_STN_DIST (distance to nearest fire station)
The distance to the nearest fire station is related to the speed of response to an incident at its very beginning. In some cases, a rapid response can eliminate a fire threat before it can cause damage to structures. Greater distances from fire stations are assigned higher point values than lesser distances in the overall rating.
WATER_DIST (distance to nearest potential water source)
The availability of water can increase suppression effectiveness. The distance to an accessible water source suitable for dip or draft is used to assign a rating.
TOPO_POS (topographic position)
A topographic position index7, or TPI, divides the landscape into different terrain types, based on slope position. Ridges and peaks are more susceptible to wildfire than valley floors, especially if surrounded by large areas of lower terrain. TPI is calculated for every landscape pixel, from which a representative rating for every polygon is then derived.
BURNABLE
An area's wildfire risk can be mitigated if it includes, or is adjacent to, non-burnable features. Golf courses, open water, agriculture, and bare ground all limit potential exposure to wildfire. The percentage of burnable versus non-burnable area is calculated inside and 0.25 miles beyond every polygon, and a risk rating is assigned based on this balance. As with all other mitigation outputs, a lower rating value indicates a lower associated risk.
Urban conflagration outputs
STR_THREAT (Structure Threat)
One of two inputs to the urban conflagration factor in Wildfire Risk Extreme, Structure Threat operates by changing houses into fuel and calculates a spotting distance, inside of which more houses could burn. This factor is a proxy for how deep inside a city an urban conflagration event might penetrate.
H2H_THREAT (House to House Threat)
This input relies heavily on the density of structures. Urban conflagration is more likely to continue in areas where radiant heat and heavy embers from neighboring structures are more pronounced – in other words, where the distance between structures is least. This input is a modifier to the penetration distance-calculated Structure Threat. It allows areas of lesser density (commercial areas, parks, etc.) to reduce the momentum of urban conflagration as it proceeds from its edge and deeper into a city.