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* Metric Name: Mean Percent FRI Departure, Since 1908  

* Tier: 3  

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

* Unit Of Measure: Percent (-100% to 100%), departure from mean FRI  

* Represent element and pillar: No  

* Type and distribution of data: Normal distribution representing percentages.  

* Translation: Where is the fire return interval within the historical range?  

* Translation method and outcome: Raw data values translated to range from +1 to -1 representing more favorable to less favorable conditions, respectively. **** The proposition of more favorable is based on the objective of being within 33% (more or less frequent) of the average historical fire return interval. The raw data range from -98.44 to 90.35. More favorable (translated to +1) set at –33 to +33% of fire return interval, less favorable (translated to -1) set at < -67% for too frequent fire, and >67% for too infrequent fire, based on FRID condition classes. 

Figure . Histogram and scoring criterion of mean percent fire return interval
departure, since 1908 across the Southern California.

Figure 87. Histogram of translated mean percent fire return interval
departure, since 1908 across the Southern California.

Figure 88. Maps displaying raw metric and translated metric of mean percent
fire return interval departure, since 1908 across the Southern California.

  

* Metric Definition and Relevance: This metric, mean percent FRID, is a measure of the extent to which contemporary fires (i.e., since 1908) are burning at frequencies similar to the frequencies that occurred prior to Euro-American settlement, with the mean reference FRI as the basis for comparison. Mean PFRID is a metric of fire return interval departure (FRID) and measures the departure of current FRI from reference mean FRI in percent.  

* Credits: Fire History (2022), CAL FIRE Existing Vegetation (CALVEG 2011), USDA Forest Service, Region 5, MARS Team