Wildfires Are Burning Less Frequently and More Severely in the Western US: An Integrative Approach to Calculating Fire-Regime Departures

Background Changing climate, vegetation, and fire exclusion are altering and homogenizing fire regime attributes compared to historical conditions. Fire-regime changes are commonly quantified using departure metrics, which are often based on measures of central tendency (i.e., the mean). These metrics can mischaracterize complex changes to the distributional characteristics of fire regime attributes. Results Here we develop a fire regime departure metric that quantifies non-parametric distributional changes to fire regime attributes. We use this departure metric to compare fire frequency and severity between historical (~ 1600–1880) and contemporary (1980–2021) time periods in western US forests. Our analysis revealed that 89% of western US forests are experiencing less frequent fire and that departures in fire severity tend to increase with human land use intensity. We also evaluated prioritization within the Wildfire Crisis Mitigation plan and found that priority landscapes are, on average, more departed than non-priority landscapes. We found that previously developed fire regime departure metrics underestimate departures in frequent fire forests and overestimate departures in infrequent fire forests. Conclusions By leveraging our distributional metrics, land managers can more effectively target restoration efforts, such as intentional fire use and mechanical thinning, to restore historical fire regimes and bolster the resilience of fire-prone landscapes.