Simulating the Potential for Invasive Grass Expansion to Alter Wildfire Behavior in Southern California With WRF‐Fire

Abstract

Invasion by non‐native annual grasses poses a serious threat to native vegetation in California,facilitated through interaction with wildfires. Our work is the first attempt to use the coupled fire‐atmospheremodel, WRF‐Fire, to investigate how shifts from native, shrub‐dominated vegetation to invasive grasses couldhave affected a known wildfire event in southern California. We simulate the Mountain Fire, which burned>11,000 ha in July 2013, under idealized fuel conditions representing varying extents of grass invasion.Expanding grass to double its observed coverage causes fire to spread faster due to the lower fuel load in grassesand increased wind speed. Beyond this, further grass expansion reduces the simulated spread rate because lowerheat release partially offsets the positive effects. Our simulations suggest that grass expansion may generallypromote larger faster‐spreading wildfires in southern California, motivating continued efforts to contain andreduce the spread of invasive annual grasses in this region.