The 1/9 Debris Flow was triggered by a rare meteorological event following a high-intensity wildfire. The meteorological event, known as a Narrow Cold Frontal Rainband (NCFR), occurred when a narrow band of intense convection and rainfall built up along a cold front at around 1 a.m. on January 8, 2018. Moving east off the Pacific, the NCFR made initial landfall at Point Conception. As the storm progressed over land, the NCFR began to weaken and break apart, delivering heavy rains of over a dispersed area. However, as the mass of rain moved further eastward, it began to rapidly recondense, forming an atmospheric river directly over Santa Barbara and Montecito, dumping .66 inches of rain in 5 minutes.
Less than a month prior, the monstrous Thomas Fire had ravaged the mountains above Montecito, Summerland, and Carpentaria. The fire’s extremely high heat scorched the soil and caused the buildup of water-repellent ash that dramatically increased the rate of runoff carrying mud, burned trees, and large boulders down the mountain canyons.
A January 5 press conference focused on the substantial risk of high-intensity flooding. On January 7, mandatory and voluntary evacuations were issued for the Montecito foothills. The following day, law enforcement began door-to-door evacuation notifications. At approximately 3:30 a.m. on January 9, the brunt of the storm hit Montecito, Summerland, and Carpinteria, and causing millions of tons of water, rock, logs, and mud to come rushing down the mountain canyons.
Montecito was hit the hardest, its creeks becoming quickly overwhelmed and bridges clogged. The leading edges of several debris flows that rushed down a handful of major watersheds measured 30 feet deep in some areas. Entire neighborhoods were obliterated. About 100 homes were destroyed, and some 500 damaged. 23 residents died; two bodies, both children, remain unaccounted for. Many residents, some with traumatic injuries, were trapped on their roofs or within collapsed structures. Highway 101 at the Olive Mill Road overpass was flooded; both directions were shut down for two weeks.
Utilities were offline for several days, and major flooding and deposited mud and debris and downed power lines rendered many roads impassable. On January 11, Montecito was declared a Public Safety Evacuation Zone and remained off limits to the general public for two weeks as recovery crews worked to get services back online.
The 1/9 Debris Flow was the worst natural disaster in Santa Barbara County history.