Risk Metrics Defined
In FireRisk, prediction impacts are computed based on the final perimeter of the 8-hr unsuppressed fire simulation.
The following impacts are calculated:
Note: The "expected" terminology originates from the statistical expectation which is the probability of an event multiplied by its consequence. All the expected risk metrics are calculated with this methodology of POF * consequence.
Fire Size Potential - Total simulation size in acres. The Fire Size Potential represents the actual simulated acreage of a fire based on the local fuels, weather, and terrain starting from an ignition at a specific location and time.
Expected Fire Size Potential - The product of the daily probability of fault (POF) and the hourly fire size potential. The purpose of this layer is to highlight the assets that are in an elevated state of both outage potential and consequences if a fire were to occur.
Population Impacted - Total population impacted by the simulation footprint.
Expected Population Impacted - Product of the daily probability of fault (POF) and the hourly simulated population impacts. The purpose of this layer is to highlight the assets that are in an elevated state of outage potential and consequences if a fire were to occur.
Buildings Threatened - Total number of buildings threatened by the simulation footprint.
Expected Buildings Threatened - Number of buildings that may be impacted for each simulation.
Estimated Buildings Destroyed - Estimated number of buildings destroyed for each simulation, derived using Building Loss Factor (BLF) data assigned to each building.
Expected Buildings Destroyed - Product of the daily probability of fault (POF) and the hourly estimated buildings destroyed. The purpose of this layer is to highlight the assets that are in an elevated state of outage potential and consequences if a fire were to occur.
Fire Potential Index - The Fire Potential Index (FPI) quantitatively estimates the fire activity potential territory-wide and leverages hourly 1km weather data and a remote-sensed daily fire occurrence dataset (from 2012 to present) to train a machine learning model to predict potential fire activity across the landscape. This model quantifies non-linearities between, weather, fuel and topography, and fire growth. We analyzed the FPI performance through verification of results with more than 10+ years of FPI data and a team of experts in fire science daily conduct validation of the index with past major fires. These categories represent the percentile of the FPI index within the domain (see example in the following table):
Some customers have incorporated their proprietary FPI for use in their Technosylva products.
Fire Behavior Index - The Fire Behavior Index (FBI) is computed using the average Flame Length and Rate of Spread on the fire front during the whole duration of the fire (the 8-hr unsuppressed fire simulation). It is calculated based on the Rate of Spread of the fire in chains per hour (80 ch/hr = 1 mi/hr), and Flame Length in ft. These values have a direct relation to suppression activities, as the commonly used Hauling Chart summarizes. Essentially it details how large and fast-moving the flames are over the burn duration.
The different values of FBI vary from 1 (Low) to 5 (Extreme) as shown in the next table.
FBI Class | Description | |
1 | LOW | Fire will burn and will spread however it presents very little resistance to control and direct attack with firefighters is possible |
2 | MODERATE | Fire spreads rapidly presenting moderate resistance to control but can be countered with direct attack by firefighters |
3 | ACTIVE | Fire spreads very rapidly presenting substantial resistance to control. Direct attack with firefighters must be supplemented with equipment and/or air support. |
4 | VERY ACTIVE | Fire spreads very rapidly presenting extreme resistance to control. Indirect attack may be effective. Safety of firefighters in the area becomes a concern |
5 | EXTREME | Fire spreads very rapidly presenting extreme resistance to control. Any form of attack will probably not be effective. Safety of firefighters in the area is of critical concern. |
Initial Attack Assessment - Provides an estimation of the difficulty of fire control in the first 1-2 hours after ignition time, ranging from 1 to 5. The higher the value, the more likely the fire is to escape the initial response ending in a potential threat.
Rate of Spread (ch/h) - The speed with which the fire is moving away from the site of origin. Calculated as an average value at the front of the fire.
Flame Length (ft) - The distance measured from the average flame tip to the middle of the flaming zone at the base of the fire. Calculated as an average value at the front of the fire.
Response Complexity - Consequence metric for individual fire spread predictions that evaluates the complexity of fire response during the first 2 hours after ignition. It combines different factors: terrain difficulty, fire behavior, initial growth behavior, number of buildings impacted, number of firefighting resources, and number of active fires (simultaneity).
Probability of Fault/Failure - The daily probability of fault (POF) represents the probability of having at least one sustained fault/outage on a circuit within a 24-hour period, and displayed as the daily aggregated value. This probability is calculated from a statistical model that is trained on historical weather data, historical outages, and asset information. The purpose of this layer is to highlight the circuits that have an elevated outage probability during a wind event.
Note: not all risk metrics will be available in your version.
Territory Wildfire Risk Forecast Metrics
Extended Attack Metrics | Description |
|---|---|
Extended Attack Assessment (no units - fire activity) | Quantifies the daily fire activity potential over the territory. EAA aims to assist operational decision-making to reduce fire threats and risks. |
Evaporative Demand Drought Index (percentile) | Indicates the potential for drought emergence in short timescales. It is expressed in percentiles. When percentiles are below 30%, this indicates drought probability is lower than normal. Percentiles above 70% show drought likelihood higher than normal. |
Fuel Complexity (no units) | Measures the fuel structure type, their loads, and the time elapsed since the last fire to quantify how the fuel may affect fire behavior, type, and suppression difficulty. |
Lifted Index (°C) | Temperature difference (in Celsius) between the environment and an air parcel lifted adiabatically at a given pressure height in the troposphere. Positive values mean a stable atmosphere and negative values indicate unstable conditions. |
Convective Flag (no units) | Identifies atmospheric conditions that favor deep and moist plume growth in wildfire smoke plumes, representing the minimum heat flux required for that plume growth. Lower values indicate more unstable conditions and the potential development of convective fires. |
Terrain Difficulty Index (no units) | It reflects the difficulty of suppressing a fire given the terrain, accessibility, penetrability and fuel typology. It ranges from very low (1) to extreme (5). |
Vapor Pressure Deficit (hPa) | An indicator of the vegetation moisture status that assess water losses through evapotranspiration. It is expressed in hectopascals (hPa). Values above 25 hPa mean high transpiration (drier) and values below 7 hPa indicate low transpiration levels (wetter). Optimal transpiration rates are between 7 and 25 hPa. |
Wind Speed (mph) | Forecasted maximum hourly wind speed. |
Raw vs Percentiles
Raw: Raw values represent the deterministic fire consequence metrics for a given date and time.
Forecast Percentiles: The forecast percentiles is the percentile of fire consequence metrics considering the forecast duration.
Historical Percentiles: The historical percentiles are calculated by comparing the fire consequence metrics for a given date and time with the historical data stored in the WFA databases.