Extreme Fire Season in California: A Glimpse Into the Future?
California has been under drought conditions since 2012, and the drought worsened considerably in the winter of 2013/14 (e.g., Wang et al. 2014), which fueled an extreme fire season in 2014 (Hart et al. 2015). The early onset of the 2014 dry season (Supplemental Fig. S2.1) fueled an extraordinary jump in wildfires. Between 1 January and 20 September, the California Department of Forestry and Fire Protection reported thousands more fires than the five-year average (www.fire.ca.gov). In early August, a state of emergency was declared for a single wildfire that had burned 32 000 acres (http://gov.ca.gov/news.php?id=18645). This unusual fire season is expected to continue well through 2015. The connection between a warming climate and lengthened fire seasons may seem intuitive, given the general tendency toward a hot-and-dry climate scenario and an earlier snowmelt (Westerling et al. 2006). However, what is not yet fully understood is the extent to which the projected wetter climate in California towards the latter part of the 21st century (Neelin et al. 2013) could affect wildfire risk in the future; this historical drought and unusual fire season also calls attention to possible impacts from human induced climate change. Satellite merged data of burned area from the fourth generation of the Global Fire Emissions Database (GFED4; Giglio et al. 2013) was analyzed (online supplemental material). Because the GFED4 product may underestimate wildfire extent due to its limit in the minimum detectable burned area and obscuration by cloud cover, the Keetch–Byram Drought index (KBDI; Janis et al. 2002; Keetch and Byram 1968), routinely used by the United States Forest Service for monitoring fire risk, was included as well. The KBDI is computed with both the observational and simulated daily precipitation and maximum surface temperature. Observational dataset is from the North American Land Data Assimilation phase 2 (NLDAS2; Xia et al. 2012).