Incorporating Anthropogenic Influences into Fire Probability Models: Effects of Human Activity and Climate Change on Fire Activity in California

Abstract

The costly interactions between humans and wildfires throughout California demonstrate the need to understand the relationships between them, especially in the face of a changing climate and expanding human communities. Although a number of statistical and process-based wildfire models exist for California, there is enormous uncertainty about the location and number of future fires, with previously published estimates of increases ranging from nine to fifty-three percent by the end of the century. Our goal is to assess the role of climate and anthropogenic influences on the state’s fire regimes from 1975 to 2050. We develop an empirical model that integrates estimates of biophysical indicators relevant to plant communities and anthropogenic influences at each forecast time step. Historically, we find that anthropogenic influences account for up to fifty percent of explanatory power in the model. We also find that the total area burned is likely to increase, with burned area expected to increase by 2.2 and 5.0 percent by 2050 under climatic bookends (PCM and GFDL climate models, respectively). Our two climate models show considerable agreement, but due to potential shifts in rainfall patterns, substantial uncertainty remains for the semiarid inland deserts and coastal areas of the south. Given the strength of human-related variables in some regions, however, it is clear that comprehensive projections of future fire activity should include both anthropogenic and biophysical influences. Previous findings of substantially increased numbers of fires and burned area for California may be tied to omitted variable bias from the exclusion of human influences. The omission of anthropogenic variables in our model would overstate the importance of climatic ones by at least 24%. As such, the failure to include anthropogenic effects in many models likely overstates the response of wildfire to climatic change.

Impact of anthropogenic climate change on wildfire across western US forests

“…Although numerous studies have projected changes in burned area over the twenty-first century due to ACC, we are unaware of other studies that have attempted to quantify the contribution of ACC to recent forested burned area over the western United States. The near doubling of forested burned area we attribute to ACC exceeds changes in burned area projected by some modeling efforts to occur by the mid-twentyfirst century (29,30), but is proportionally consistent with midtwenty-first century increases in burned area projected by other modeling efforts (17,(31)(32)(33).…”

Climate change vulnerability assessment of forests in the Southwest USA

“…The factors catalysing mortality in these forests are the subject of intensive current research and include physiological stress from increasingly hot droughts and secondary effects such as increased beetle outbreaks and fire frequency or intensity (e.g. Allen et al 2015;Anderegg et al 2015;Moritz et al 2014;Mann et al 2016;Asner et al 2016). This paper adds spatial predictions of the forested areas most likely to experience climatic stress to the context, which represents in situ risk.…”

Human-caused fire occurrence modelling in perspective: a review

“…Proximity to campgrounds (Pew and Larsen 2001;Gonzalez-Olabarria et al 2011;Mann et al 2016) or fishing areas (Chang et al 2013;Sitanggang et al 2013) is often related to negligent or careless fires. The relationship between HCFs and population density varies depending on the ignition cause.…”