Abstract: |
Average annual area burned on USDA Forest Service lands in the western United States from the late 1980s to the present have increased by a factor of three over the 1970s. Perhaps more important from a management standpoint, interannual variability has increased by an order of magnitude over the same period, greatly complicating budgeting for wildfire suppression.Pervasive human interventions in western U.S. ecosystems have had profound effects on fire regimes in the region. Despite these effects, we demonstrate that wildfire season severity is still strongly linked to climate variability, and that climate-fire relationships can be used to forecast wildfire season severity. Furthermore, we have found that an increased incidence of extreme moisture anomalies in the western United States may account for some of the recent changes in annual area burned and suppression cost. We use records of relative humidity, wind speed, precipitation, snow melt timing and drought indices to describe the recent evolution of fire regimes in the western United States, and discuss their implications for fire management. Using historical climate records of the 20th century and proxy climate records of the 18th and 19th centuries, we seek to put recent fire seasons’ severity in a long-term perspective. Our statistical models estimate what current managed fire regimes would look like in terms of annual area burned and suppression cost expenditures for the range of climate variability observed over the past three centuries. We use proxy paleofire records based on fire scar chronologies from the 18th and 19th centuries to validate our models. These tools allow fire managers to consider a broader range of natural variability in fire regimes for planning purposes than the short, incomplete historical record allows. |
