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* Metric Name: Mean Percent FRI Departure, Since 1970 *  

* Tier: 2  

* 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: Yes  

* Type and distribution of data: Bimodal 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. 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. These interpretations correspond to well-established FRI condition classes (see below). FRID itself is an interpretation of conditions that are expected to be more resilient based on historical fire regimes. Alternative approaches could be to broaden the interpretation of less favorable (-1) out to <-100% sand >100%, but then they would not correspond to FRI condition classes. FRID average values and condition classes based on empirical data (see metric dictionary for raw data for citations). 

Figure . Histogram and scoring criterion of mean percent fire return interval
departure, since 1970 across Southern California.

Figure 90. Histogram of translated current mean percent fire return interval
departure, since 1970 across Southern California.

Figure 91. Maps displaying raw metric and translated metric of mean percent
fire return interval departure, since 1970 across Southern California.

  

* Metric Definition and Relevance: Percent FRID (PFRID) quantifies the extent to which recent fires (i.e., since 1970) are burning at frequencies similar to those that occurred prior to Euro-American settlement, with the mean reference FRI as the basis for comparison. Mean PFRID 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