EvacuationDisasters: To Flee or Not to Flee
The Montecito debris flows that occurred in January 2018 were the result of a rare confluence of two uncommonly severe events: the Thomas Fire — at that time the largest wildfire in California history — which for weeks burned through Ventura and Santa Barbara counties; and the intense winter storm that followed. Researchers say it is important to keep residents — and emergency management offices — informed about rare but potentially lethal natural events.
A new study by UC Santa Barbara researchers speaks to the importance of public awareness programs in keeping residents — and emergency management offices — informed about rare but potentially lethal natural events in their area.
The paper is published in the International Journal of Disaster Risk Reduction.
The work is part of an ongoing effort to understand and improve how communities prepare for future disasters. “There were a lot of problems because people didn’t know what to do,” said Keller. “We need to learn from that.”
The Montecito debris flows that occurred in January 2018 were the result of a rare confluence of two uncommonly severe events: the Thomas Fire — at that time the largest wildfire in California history — which for weeks burned through Ventura and Santa Barbara counties; and the intense winter storm that followed, at one point dumping half an inch of rain in a five-minute period on the newly charred mountainside. Add to that combination a topography that is prone to swift floods, as rain-swollen creeks jump their banks, creating new channels.
“All of Montecito was built on these alluvial fans,” Keller said. “The whole place.”
Residents of Montecito were made aware of the possible disaster and given an evacuation order the day before the storm’s arrival, but many chose to stay.
In surveys and interviews with hundreds of respondents, the researchers sought the residents’ reasons for choosing not to evacuate. Lack of knowledge of debris flows seems to have contributed to a false sense of security.
“From the interviews, we learned that they did not know about previous debris flows in Santa Barbara County and in Montecito, and that they didn’t know what a debris flow was,” said Goto, the lead author of the study, which is likely the first paper to dive into the physical systems of and the behaviors surrounding catastrophic debris flows. “And so, they did not understand their risk.”
Unlike wildfires — regular events for Californians — debris flows of the magnitude that occurred in Montecito are exceptionally rare, with an average recurrence interval of about 1,700 years, and a 6 percent chance of such a catastrophic event occurring in the next 100 years, according to the paper. However, said the researchers, it is important to remember that rare events based on probability do not mean they cannot occur again at shorter time periods. Smaller debris flows are common when rains follow wildfires, Keller pointed out, but they
