Communicating the Misunderstood Hazard of Post-Fire Debris Flows to a Diverse Population: Lessons Learned from a Catastrophic Event in Santa Barbara County

In the early hours of January 9, 2018, a devastating debris flow was triggered by extremely heavy rain on the slopes above Montecito, CA, which swept down normally dry creek beds toward the Pacific Ocean destroying homes and cars, and resulting in 21 fatalities and 2 additional missing and presumed deceased. Generated from the second largest wildfire in California history (Thomas Fire), towering walls of mud, ash, boulders, and trees, as high as 30 feet tall scoured homes from foundations, twisted cars into pretzels, and buried streets in thick debris. In large part due to the Decision Support Services delivered by the Los Angeles/Oxnard National Weather Service (NWS) office starting up to six days prior to the event, on January 7th county officials issued a combination of mandatory and voluntary evacuation orders across a population of 23,000 residents that live below the Thomas burn scar in coastal Santa Barbara County, and including much of the city of Montecito. However, officials estimated that just 11 percent of those in the evacuation areas actually heeded those warnings and left the area prior to the storm’s arrival.

Despite the evacuation orders and although community preparedness agencies and the NWS sent strong messages about the potential risk of damaging debris flows days in advance, did the public listen and properly understand the potential threat? What kept the vast majority of people in their homes instead of seeking safe areas from this hazard? Several factors may have contributed. Namely, people in the path of this destruction had been evacuated or impacted by the Thomas Fire just 3 weeks prior to the debris flow. Thus evacuation fatigue during the holiday season, and the lesser known hazard of post fire debris-flows all likely played a role in the limited public response to this well-advertised threat.

Montecito, CA, is well-known for its large luxury homes, lush landscapes, and movie-star residents, but it is also home to many blue collar families living in smaller dwellings all within a stone’s throw of watershed drainages from the nearby Santa Ynez Mountains. The January 9^th debris flow was not selective in its path of destruction through these Montecito neighborhoods. When a river channel became blocked or filled, the debris flow found a new path well outside of the normal drainage, which damaged many large estates along with clusters of smaller homes. The resulting fatalities from the debris flow ranged in age from the very young (2 years old) to the elderly (89 years old), and many of those impacted were concentrated in and near smaller properties, presumably occupied by bi-lingual speaking residents. Following January 9^th, several questions arose about debris flow preparedness and education messaging in languages other than English. There is a need to better understand cultural differences in decision-making and risk perception, and to discover appropriate avenues for hazard communication that reach all population groups.

Post-event social science surveys conducted among residents within the evacuation areas have revealed how people mis-interpreted evacuation orders and the perceived debris flow threat prior to the event in the Montecito area. Southern Californians are very experienced in wildfire preparedness and evacuations, but the terminology of debris flows and the potential scale of destruction from them is not well known. Numerous issues discovered from the surveys will need to be investigated to better prepare communities for future debris flows; provide adequate and timely outreach in multiple languages, develop innovative ideas to visualize intense rainfall and the differences between debris flow and flash floods, improve public understanding of evacuation orders, and establish consistent messaging between public agencies. The Montecito debris flow was an unimaginable disaster that few were prepared for following one of the largest wildfires in state history.

In addition to providing an overall synopsis of this catastrophic event and describing the Decision Support Services provided by the NWS, this presentation will review the preparations undertaken before the event, the social science findings in its aftermath, and present possible ideas on how to better ensure the public receives, understands, and takes action when facing this rare but deadly natural hazard.