Post-fire debris flows of 9 January 2018, Thomas Fire, southern California: initiation areas, precipitation and impacts

Abstract

The post-fire debris flows of 9 January 2018 killed 23 people, destroyed over 130 homes, and caused severe damage to infrastructure in Montecito and Carpinteria, California. Highway 101 was closed for 13 days, significantly impacting transportation and commerce in the region. Collectively, debris flows from this event are comparable in magnitude to the largest documented post-fire debris flows in the state, inundating over 4 km2 of land, and costing the Santa Barbara region over half a billion dollars in debris removal and damages to homes and infrastructure. Here, we document the extent and magnitude of inundation areas, debris- flow volumes, and source areas. Additionally, we describe the atmospheric conditions that generated intense rainfall and use precipitation data to compare debris-flow source areas with spatially associated peak 15-minute rainfall depths. We use a compilation of debris-flow damages to summarize economic impacts associated with the event.