- Metric Name:  Mean Percent FRI Departure, Since 1908

- Data Vintage:  2021

- Unit Of Measure: Percent

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 mean reference FRI in percent.

Creation Method: The current FRI is calculated by dividing the number of years in the fire record (e.g., 2019-1908=112 years inclusive) by the number of fires occurring between 1908 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). Instead, the following formulas are used to calculate Mean PFRID:

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

For areas dominated by PFRs with a mean reference FRI greater than 112 years, and that have not burned in the period of historical record considered in this analysis (i.e., since 1908), the FRID is assumed to equal zero.

- Credits:  Fire History (2021), CAL FIRE

CALFIRE, Department of Forestry and Fire Protection: The State of California and the Department of Forestry and Fire Protection make no representations or warranties regarding the accuracy of data or maps. The user will not seek to hold the State or the Department liable under any circumstances for any damages with respect to any claim by the user or any third party on account of or arising from the use of data or maps.



Existing Vegetation (CALVEG 2011), USDA Forest Service, Region 5, MARS Team

USDA Forest Service - Region 5 - Pacific Southwest Region: The USDA Forest Service makes no warranty, expressed or implied, including the warranties of merchantability and fitness for a particular purpose, nor assumes any legal liability or responsibility for the accuracy, reliability, completeness, or utility of these geospatial data, or for the improper or incorrect use of these geospatial data. These geospatial data and related maps or graphics are not legal documents and are not intended to be used as such. The data and maps may not be used to determine title, ownership, legal descriptions or boundaries, legal jurisdiction, or restrictions that may be in place on either public or private land. Natural hazards may or may not be depicted on the data and maps, and land users should exercise due caution. The data are dynamic and may change over time. The user is responsible to verify the limitations of the geospatial data and to use the data accordingly.