* Metric Name: Current Fire Return Interval Departure, Since 1970  

* Tier: 3  

* Data Vintage: 2021  

* Unit Of Measure: Average Years

The fire return interval departure (FRID) analysis quantifies the difference
between current and pre-settlement fire frequencies, allowing managers to
target areas at high risk of threshold-type responses owing to altered fire
regimes and interactions with other factors. This is a measure of the extent
to which contemporary fires (i.e. since 1970) 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. With this metric,
mPFRID_1970, the same formulas are used 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.

* Creation Method: Current fire return interval 1970 is calculated by dividing the number of years in the fire record by the number of fires occurring between 1970 and the current year in a given area plus one.

 _CurrentFRI_1970 = Number of years/Number of Fires +1_

  

* 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