Spatial patterns and controls on burned area for two contrasting fire regimes in Southern California

Spatial patterns and controls on burned area for two contrasting fire regimes in Southern California N. R. Faivre, 1, † Y. Jin, 2 M. L. Goulden, 1 and J. T. Randerson 1 1 Department 2 Department of Earth System Science, University of California, Irvine, California 92697-3100 USA of Land, Air and Water Resources, University of California, Davis, California 95616-8627 USA Citation: Faivre, N. R. , Y. Jin, M. L. Goulden, and J. T. Randerson. 2016. Spatial patterns and controls on burned area for two contrasting fire regimes in Southern California. Ecosphere 7(5):e01210. 10.1002/ecs2.1210 Abstract. An improved understanding of the mechanisms that regulate wildfire risk at local to regional scales is needed for the design of effective fire and ecosystem management. We investigated the spatial distribution of burned area in Southern California during 1960–2009 using five different data-­driven meth- ods: multiple linear regression, generalized additive models (GAMs), GAMs with spatial autocorrelation, non-­linear multiplicative models, and random forest models. We used each method to separately develop burned area risk maps for Southern California’s two distinct wildfire regimes: Santa Ana (SA fires), which occur during high wind events mostly in autumn, and non-­Santa Ana fires (non-­SA fires), which occur mostly during the hot and dry Mediterranean-­climate summer. The different methods explained 38–63% of the spatial variance in burned area for SA fires and 21–48% for non-­SA fires. The two fire regimes had contrasting drivers, with Fosberg fire weather index, relative humidity, minimum temperature, and dis- tance to housing most important for SA fires, and shrub cover, road density, and distance to minor and major roads most important for non-­SA fires. Our modeling framework carries implications for the strate- gic placement of fire suppression resources, and for prevention planning in areas facing increasing human and climate pressures. Key words: biophysical drivers; fire frequency; geospatial regression models; human influence; Mediterranean ­ecosystems; Santa Ana fires; wildfire risk; wildland–urban interface. Received 22 July 2015; accepted 29 July 2015. Corresponding Editor: D. P. C. Peters. Copyright: © 2016 Faivre et al. This is an open access article under the terms of the Creative Commons Attribution ­License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. † E-mail: belotte.faivre@gmail.com I ntroduction loss and multiple fatalities (Brillinger et al. 2009, Keeley et al. 2009). Spatial and temporal variabil- ity in burned area within the region depends on ignition, meteorology, vegetation characteristics, topography, and fire suppression (Davis and Mi- chaelsen 1995, Zedler and Seiger 2000, Moritz et al. 2004). Large areas of wildland–urban inter- face further contribute to variability in burned area as a consequence of ignition probability, landscape fragmentation, and access points for suppression. Interactions between the envi- ronmental and human controls on wildfire are Southern California is prone to recurrent wild- land fire that strongly influences ecosystem pro- cesses and vegetation dynamics. Over the past 50 yr, an average of 40 large fires (>40 ha each) occurred each year, resulting in a mean burned area of 53 300 ha per yr (Jin et al. 2014). Despite considerable investment in fire suppression, fire perimeter data sets show an increasing trend in burned area since 1980 (Westerling 2006, Jin et al. 2014). These fires have caused extensive property v www.esajournals. org May 2016 v Volume 7(5) v Article e01210