CAN PAST POST-FIRE EROSIONAL EVENTS BE USED TO PLAN FOR THE FUTURE?

Hazards associated with wildfire are exacerbated at the wildland urban interface (WUI). Planning for larger, more severe fires and prolonged fire seasons requires considering the increased risk of fire-induced debris flows. Like many cities in the western US (e.g. Denver, Reno, Salt Lake City), the Boise WUI is located at the base of a mountain front. Range front vegetative communities in these western US WUI’s are typified by shrubs (sagebrush steppe) and grasslands at lower elevations, with open forests at higher elevations and on north-facing slopes. Despite WUI development increasing concurrently with fire and erosion hazards in these ecosystems, most erosion and fuel models are developed for forested ecosystems. Here we present post-fire debris flow hazard scenarios for the Boise, Idaho foothills. By varying fire severity and precipitation intensity, fire managers can plan for a variety of scenarios using models developed in forested ecosystems (Cannon et al., 2010). We validate the model’s estimate of sediment volume by comparing model predictions to a historic mudflow event that occurred shortly after a 7000 acre fire in the Boise foothills in 1959. We found that volume estimates fell well within an order of magnitude of the recorded volumes eroded from the foothills during the 1959 event. These results validate the use of post-fire debris flow models in rangeland (vs.forest) settings. In addition, this work provides an example of how post-fire erosion models can be applied in pre-fire settings for planning purposes, allowing time to validate the model results with locally relevant historic records.