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* Metric Name: Damage Potential  

* Tier: 1  

* Data Vintage: 08/2023. Includes disturbances through the end of 2022  

* Unit Of Measure: Relative index, low to high  

* Metric Definition and Relevance: This metric combines two data layers; one is the Wildland Urban Interface (WUI) as defined by Carlson et al. 2022 (see WUI definition section for more information), and a second data layer, Damage Potential (DP), developed by Pyrologix LLC. The WUI includes the intermix and interface zones which collectively identify areas where structures occur. The distance selected for the interface definition is based on research from the California Fire Alliance suggesting that this is the average distance firebrands can travel from an active wildfire front. 

The composite Damage Potential (DP) dataset represents a relative measure of
wildfire’s potential to damage a home or other structure if one were present
at a given pixel, and if a wildfire were to occur (conditional exposure). It
is a function of ember load to a given pixel, and fire intensity at that
pixel, and considers the generalized consequences to a home from fires of a
given intensity (flame length). This index does not incorporate a measure of
annual wildfire likelihood.

  

* Creation Method: This metric represents DP for WUI areas only. DP values were binned based on the following ranges into 6 classes and assigned class names. 

  * 0 (None): Values = 0
  * 1 (Very Low): Values 0.01 to 20
  * 2 (Low): Values 20 to 35
  * 3 (Moderate): Values 35 to 50
  * 4 (High): Values 50 to 80
  * 5 (Very High): Values 80+

The current delineation of the WUI (Carlson et al. 2022) uses a mapping
algorithm with definitions of the WUI; two classes of WUI were identified:

  * the intermix, where there is at least 50% vegetation cover surrounding buildings
  * the interface, where buildings are within 2.4 km (1.5 miles) of a patch of vegetation at least 5 km2 in size that contains at least 75% vegetation.

Both classes required a minimum building density of 6.17 buildings per km2
(using a range of circular neighborhood sizes).

Damage Potential (DP) data was produced by Pyrologix LLC, a wildfire threat
assessment research firm, as part of a spatial wildfire hazard assessment
across all land ownerships for the state of California. The ongoing work
generally follows the framework outlined in Scott and Thompson (2013), with
custom methods and significant improvements developed by Pyrologix. The
project generally consists of three components: fuelscape calibration and
updates, wildfire hazard assessment, and risk assessment. It utilizes a
combination of wildfire models and custom tools, including WildEST (Wildfire
Exposure Simulation Tool), a custom modeling tool developed by Pyrologix
(Scott, 2020). To date, this work has resulted in a wide variety of spatial
data layers related to wildfire hazard and risk, including Damage Potential
(DP), representing conditions prior to the 2023 fire season. Work to date has
been funded by the USDA Forest Service Region 5, the California Energy
Commission, and the USDI Bureau of Land Management with data contributions
from CAL FIRE. Please reference the Pyrologix 2021 project report (Volger et
al., 2021) for more information about the project or WildEST analysis.

Damage Potential (DP) is a proprietary index developed by Pyrologix LLC
representing wildfire’s potential to damage a home or other structure if a
wildfire were to occur (conditional exposure). It is a function of ember load
to a given pixel and fire intensity at that pixel, and it considers the
generalized consequences to a home from fires of a given intensity (flame
length). DP is calculated based on two other datasets developed by Pyrologix:
conditional risk to potential structures (cRPS) and conditional ember load
index (cELI).

cRPS represents the potential consequences of fire to a home at a given
location if a fire occurs there and if a home were located there. It is a
measure that integrates wildfire intensity with generalized consequences to a
home on every pixel. Wildfire intensity (flame length) is calculated using
Pyrologix’ WildEST tool. WildEST is a scripted geospatial process used to
perform multiple deterministic simulations under a range of weather types
(wind speed, wind direction, fuel moisture content). Rather than weighting
results solely according to the temporal relative frequencies of the weather
scenarios, the WildEST process integrates results by weighting them according
to their weather type probabilities (WTP), which appropriately weights high-
spread conditions into the calculations. For fire-effects calculations,
WildEST generates flame-length probability rasters that incorporate non-
heading spread directions, for which fire intensity is considerably lower than
at the head of the fire.

The response function characterizing potential consequences to an exposed
structure is applied to fire effects flame lengths from WildEST for all
burnable fuel types on the landscape regardless of whether an actual structure
is present or not. The response function does not consider building materials
of structures and is meant as a measure of the effect of fire intensity on
structure exposure. The response function is provided below:

  * Flame length probability of 0-2 ft: -25
  * Flame length probability of 2-4 ft: -40
  * Flame length probability of 4-6 ft: -55
  * Flame length probability of 6-8 ft: -70
  * Flame length probability of 8-12 ft: -85
  * Flame length probability of >12 ft: -100

These results were calculated using 30m fire-effects flame-length
probabilities from the WildEST wildfire behavior results and then further
smoothed.

cELI is also calculated in WildEST, and represents the relative ember load per
pixel, given that a fire occurs, based on surface and canopy fuel
characteristics, climate, and topography within the pixel. Units are the
relative number of embers. cELI is based on heading-only fire behavior.

Damage Potential is then calculated as the arithmetic mean of cELI and cRPS
for each pixel across the landscape as follows:

𝐷𝑃 = 𝑐𝑅𝑃𝑆 + 𝑐𝐸𝐿𝐼/2

Although flame length and its potential impact to structures is a function of
the fire environment at the subject location only, ember load is a function of
ember production and transport in the area surrounding the subject location. A
location with light fuel (and therefore low flame length) could still have
significant Damage Potential if surrounded by a fire environment that produces
copious embers.

  

* Credits: Pyrologix, LLC \--James Newman (California State BLM Office) jnewman@blm.gov WUI, Carlson et al, 2022 \--Carlson, Amanda R., David P. Helmers, Todd J. Hawbaker, Miranda H. Mockrin, and Volker C. Radeloff