Southern California Flooding and Mudslides (Jan 2018)

During the night of Tuesday January 9 extreme rainfall in Southern California created mudslides and flash-flooding in areas close to the burn scars of the December 2017 Thomas Fire. The most damage is reported in the affluent community of Montecito (pop. ~9,000), Santa Barbara County, located below the burn scar of the Thomas Fire. Officials report that 64 homes and 8 commercial properties have been destroyed, and 446 homes and 20 commercial properties damaged. Much of the damage is reported near the 300 block of Hot Springs Road. An exclusion area for rescue work between Hot Springs Road/Olive Mill Rd and Sheffield Drive/Ladera Lane has been set up in Montecito. Aerial footage shows a few residential structures destroyed by a fire attributed to a ruptured gas line. About 300 people were trapped in Montecito’s Romero Canyon due to impassable roads. A mudslide in nearby Carpinteria (pop. ~14,000) damaged a small, but unknown number of houses. In Los Angeles County, a mudslide damaged vehicles and caused minor damage to homes on Country Club Drive in Burbank (pop. ~100,000), which was affected by the La Tuna Canyon Fire in September 2017. A mudslide occurred on rural Topanga Canyon Boulevard, though only vehicle damage is reported at this time. Minor flooding created disruption in the customs area of Los Angeles International Airport. Many roads have been blocked, with about 30 miles of the US 101 highway closed at one point. This disruption is forecast to continue until Monday January 13 as crews clear the roads. About 6,000 homes and businesses are without power in the Montecito area, and disruptions to water, gas and telecommunications are forecast to last several days. Several California theme parks were closed by the rain, including Six Flags Magic Mountain in Valencia and SeaWorld in San Diego. At least 17 people have been killed in weather-related accidents. So far, no mudslides related to the Creek, Fish or Skirball fires of December 2017 have been reported, though warnings remain in place. Meteorological and Hydrological Context: Conditions for these mudslides were caused by a specific set of circumstances: a wet 2016-17 winter followed by a dry summer created extremely favourable wildfire conditions in California, leading to the record-breaking Southern California wildfires of December 2017. Since burned soil does not absorb rainwater well and is vulnerable to erosion, very heavy rainfall can create large volumes of mud-laden runoff and debris flow as has occurred here. The community of Montecito received more than 0.5 in (13 mm) rainfall in five minutes. Nearby Carpinteria measured almost 0.9 in (23 mm) in 15 minutes. Parts of the Thomas Fire burn area received 4 to 6 in (100 – 150 mm) rain in the 48 hours to the morning of Tuesday January 9 (local time). In December 2017 the Thomas Fire burned 281,000 acres and 1,063 structures in Santa Barbara and Ventura counties.

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