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* Metric Name: Structure Exposure Score  

* Tier: 1  

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

* Unit Of Measure: Relative index, 10 classes  

* Metric Definition and Relevance: This metric, Structure Exposure Score (SES), was developed by Pyrologix LLC. 

Structure Exposure Score is an integrated rating of wildfire hazard that
includes the likelihood of a wildfire reaching a given location along with the
potential intensity and ember load when that occurs. SES varies considerably
across the landscape.

Pyrologix uses a standard geometric-interval classification to define the ten
classes of SES, where each class break is 1.5 times larger than the previous
break. So, homes located within Class X are 1.5 times more exposed than those
in Class IX, and so on.

  1. (SES I): 0
  2. (SES II): 0.01 to 50
  3. (SES III): 50 to 75
  4. (SES IV): 75 to 113
  5. (SES V): 113 to 169
  6. (SES VI): 169 to 253
  7. (SES VII): 253 to 380
  8. (SES VIII): 380 to 570
  9. (SES IX): 570 to 854
  10. (SES X): 854+

  

* Creation Method: Structure Exposure Score (SES) is a proprietary index representing the level of wildfire exposure for a structure (e.g., a home) if one were to exist on a given pixel. It is an integrated measure that includes three components: the likelihood of a wildfire of any intensity occurring in a given year (annual burn probability), potential wildfire intensity for a given pixel, and ember load to that pixel from surrounding vegetation.

SES 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 the FSim large wildfire simulator (Finney
et al., 2011), and WildEST, 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 Structure Exposure
Score (SES), representing conditions prior to the 2020, 2021 and 2022 fire
seasons. 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.

For this project, the FSim large-fire simulator is used to quantify annual
wildfire likelihood across the analysis area. FSim is a comprehensive fire
occurrence, growth, behavior, and suppression simulation system that uses
locally relevant fuel, weather, topography, and historical fire occurrence
information to make a spatially resolved estimate of the contemporary
likelihood and intensity of wildfire across the landscape.

WildEST (Wildfire Exposure Simulation Tool) is used to quantify wildfire
intensity and ember loads across the analysis area. WildEST is a deterministic
wildfire modeling tool developed by Pyrologix that integrates spatially
continuous weather input variables, weighted based on how they will likely be
realized on the landscape. This makes the deterministic intensity values
developed with WildEST more robust for use in effects analysis than the
stochastic intensity values developed with FSim. This is especially true in
low wildfire occurrence areas where predicted intensity values from FSim are
reliant on a very small sample size of potential weather variables. It also
allows for more appropriate weighting of high-spread conditions into fire
behavior calculations. WildEST also produces indices of conditional and
expected ember production from vegetated areas (pixels) and load to other
pixels in the analysis area. Please reference the Pyrologix 2021 project
report (Volger et al., 2021) for more information on WildEST analysis.

FSim was run for the CAL 2022 fuelscape at 120m resolution. WildEST was run
for the CAL 2022 fuelscape at 30-m resolution. Both models utilized gridded
hourly historical California weather data provided by CALFIRE. Results for
annual burn probability (FSim), fire intensity (WildEST) and ember load
(WildEST) were used to create Structure Exposure Score.

  

* Credits: * Pyrologix, LLC