Abstract
Climate change is anticipated to influence future wildfire activity in complicated, and potentially unexpected ways. Specifically, the probability distribution of wildfire size may change so that incidents that were historically rare become more frequent. Given that fires in the upper tails of the size distribution are associated with serious economic, public health, and environmental impacts, it is important for decision-makers to plan for these anticipated changes. However, at least two kinds of structural uncertainties hinder reliable estimation of these quantities—those associated with the future climate and those associated with the impacts. In this paper, we incorporate these structural uncertainties into projections of very-large fire (VLF)—those in the upper 95th percentile of the regional size distribution—frequencies in the Continental United States during the last half of the 21st century by using Bayesian model averaging. Under both moderate and high carbon emission scenarios, large increases in VLF frequency are predicted, with larger increases typically observed under the highest carbon emission scenarios. We also report other changes to future wildfire characteristics such as large fire frequency, seasonality, and the conditional likelihood of very-large fire events.
Highlights
Representing only a small fraction of the total number of fires, very-large fires (VLFs) are events often associated with dramatic economic, human health, and environmental risks that are unlike most other wildfires
The diversity of predictors used in the probability estimation tree (PET) was high, and the important meteorological variables varied by region, the summary statistic, and the type of fire probability
The importance of temperature metrics varied by the type of fire probability considered, with temperature metrics more commonly identified as the optimal split criterion in LF forests compared to VLF forests
Summary
Representing only a small fraction of the total number of fires, very-large fires (VLFs) are events often associated with dramatic economic, human health, and environmental risks that are unlike most other wildfires. The most salient and immediate economic impacts are suppression costs and property losses (Barrett 2018, [1]), which are often relatively large in VLFs compared to other smaller events (González-Cabán 1983 [2], Stephens et al, 2014 [3]). In addition to these direct costs, there is a suite of indirect economic impacts—such as damages from post-fire hazards, rehabilitation costs, lost tax and business revenue from community evacuations (Dale 2009 [4])—that are increasingly probable and costly in larger wildfires (Neary et al, 2003 [5], Peppin et al, 2011 [6], Beverly and Bothwell 2011 [7], Beverly et al, 2011 [8]). These include the production of environmental conditions conducive to the establishment of invasive species (Crawford et al, 2001 [14]), loss of ecosystem services (Rocca et al, 2014 [15]), and long-term modifications to forest structure (Haffey et al, 2018 [16])
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