Environmental and Social factors that led to the October 2017 Northern California Firestorm (Invited Presentation)

A firestorm is defined as a very intense and destructive fire usually accompanied by strong wind. The term has relational roots to the rapid, obliterating destruction of areas by fire from bombing during World War II. Overnight October 8, 2017 and the early hours of October 9 saw 17 fires ignited across Northern California with the hardest hit areas in the world-famous Napa and Sonoma wine country located about 60 miles north of San Francisco. The fires spread rapidly, devouring a conservative estimate of 49,000 acres in 12 hours, and by October 14^th, nearly 220,000 acres had burned and 118,000 people were evacuated. Forty-three people perished, which is the largest loss of life in the U.S. from a collection of wildfires since the devastating 1918 Cloquet, Minnesota, fires (453 deaths). The nearly 9,000 structures destroyed included both residential and commercial property. The Tubbs Fire was the most damaging one, causing 21 deaths and destroying 5,643 structures, including businesses. It is the single most destructive wildfire in California history. Several cause-and-effect relationships between weather, fuel and topography helped create extreme fire behavior, including fire whirls, long range spotting and heat intense enough to melt vehicles. Environmental factors in place at the time of the fires include a multi-year drought that ended in May 2016, well above normal precipitation during the 2016-17 winter season and a flash drought during the preceding summer months. Contributing factors during the first 12 hours of the event include very strong and highly sheared wind flow across complex terrain, an unusually dry overnight air mass and historically dry fuels for the time of year. Several environmental and social factors led to the major loss of life and property destruction during this firestorm event. The social factors that helped accentuate the destructive outcome will also be discussed.