Fire return interval in CA, 1908-2012

The current fire return interval is calculated by dividing the number of years in the fire record by the number of fires occurring during that time period, then adding a value of one (CurrentFRI = Number of years/Number of fires+1). This dataset is current to 2012. Although fires prior to 1908 are recorded in the fire perimeter database, they are not included in this analysis due to lack of consistency in reporting (1908 is the year that the US Forest Service began to formally record information on size and location of major fires).CurrentFRI is derived by overlaying the fire perimeters on the PFR polygons and summing the number of fires affecting each polygon after 1908.