* Metric Name: Mean Percent FRI Departure, Since 1970
* Tier: 2
* Data Vintage: 2021
* Unit Of Measure: Percent
Mean Percent FRID (meanPFRID_1970) quantifies the extent in percentage 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.
* Creation Method: The current FRI is calculated by dividing the number of years in the fire record (e.g., 2019-1970=49 years inclusive) by the number of fires occurring between 1970 and the current year in a given polygon plus one (CurrentFRI = Number of years/Number of fires +1). The mean reference FRI is an approximation of how often, on average, a given PFR likely burned in the three or four centuries prior to significant Euro-American settlement. This measure does not return to zero when a fire occurs, unlike FRID values used in some other analyses (e.g., NPS FRID Index). The following formulas are used to calculate Mean PFRID, the same as with meanPFRID but with 1970 as the baseline rather than 1908. Important note: because 1970 is the baseline for this measure, no fires before 1970 are taken into account and all PFRs start at a PFRID of zero beginning in 1970.
When current FRI is longer than reference FRI (the common condition in most
coniferous PFRs) the formula is:
_[1-(MeanRefFRI/CurrentFRI)]*100_
When current FRI is shorter than reference FRI (common in some shrub dominated
PFRs, and areas in the Wildland Urban Interface) the formula is:
_-{[1-(CurrentFRI/MeanRefFRI)]}*100_
* Credits: Fire History (2021), CAL FIRE \--Department of Forestry and Fire Protection Existing Vegetation (CALVEG 2011), USDA Forest Service, Region 5, MARS Team \--Region 5 - Pacific Southwest Region