Beyond average: New approach to calculating fire regime departures applied to Western US forests

View article.

We developed a non-parametric index of fire regime departure that quantifies distributional changes to fire regime attributes between time periods using the Earth Mover’s Distance. We used this departure metric to compare fire frequency and burn severity between historical (~1600–1880) and contemporary (1985–2021) time periods in western US forests. In addition, we compared the proposed metrics with a standard suite of measures of central tendency. Departure metrics based on measures of central tendency reported lower relative departures within frequent fire forests and higher relative departures within infrequent fire forests than the EMD-based method. We found that 89% of western US forests are experiencing less frequent and more severe wildfires than historical baselines. Large departures are associated with increased human land-use intensity, and landscapes prioritized by the Wildfire Crisis Mitigation plan are on average, more departed than non-priority landscapes.