The Northern California 2018 extreme fire season

Both 2017 and 2018 were extreme fire years in California. While this paper has focused on Northern California in 2018, Southern California that year also saw its share of extreme fire including the Ferguson (two firefighter fatalities, 19 structures destroyed, and approximately 39,000 ha burned), Cranston, and Holy Fires. On the same day as the Camp Fire, 8 November, two large fires developed in Ventura and Los Angeles County, including the Woolsey Fire (approximately 39,000 ha burned and over 1,600 structures destroyed). Following the unusually late season December 2017 Thomas Fire in the Ventura and Santa Barbara county area, a post-fire debris flow event occurred over the burn area on 9 January resulting in 23 fatalities and 246 structures destroyed (Oakley et al. 2018). Climate, fuels, and people are the three confluent factors for California’s recent destructive wildfires. The wildland–urban interface has been growing extensively within the state during the past few decades (e.g., Radeloff et al. 2018), placing people in fire-prone areas. Climate is an enabler of wildfire by providing seasonal moisture to grow fuels, and seasonal warming and drying that increases fuel flammability. Increasing temperature trends enable longer and more extreme fire seasons. California’s annual temperatures have been increasing substantially during the past four decades and are expected to continue warming this century (California’s Fourth Climate Assessment; Bedsworth et al. 2018). Abatzoglou and Williams (2016) have shown that California (as well as all of the West) has had significantly enhanced fuel aridity due to anthropogenic increases in temperature and vapor pressure deficit over the past several decades. This can also be seen in the increasing number of days of fire weather season length based on fire danger indicators (e.g., Jolly et al. 2015). Nighttime temperature trends especially may be playing an important role in more extreme fire behavior. Research is currently underway to examine the specific relationship of this warming to nighttime fuel drying and subsequent extreme fire behavior that was observed during the California 2018 fire season. An estimated 54% of California ecosystems are fire dependent and most of the rest are fire adaptive (Pyne 2016). California has always had fire given its climate, topography, and distinctive varieties of combustible vegetation. Today it is a state of nearly 40 million people, and one in four Californians live in a “high risk” wildfire area (https://www.latimes.com/local/lanow/la-me-California-braces-for-new-wildfires-20190614-story.html; accessed 24 November 2019). California insured losses in 2018 from wildfire topped $13 billion (https://www.insurancejournal.com/news/west/2019/05/08/525930.htm; accessed 24 November 2019). The year 2018 now holds the record for the most destructive wildfire, the largest wildfire, and the costliest wildfire season in California state history. © 2020 American Meteorological Society. All rights reserved.