Controls on interannual variability in lightning-caused fire activity in the western US

John T Abatzoglou,Bethany A Bradley,Jennifer K Balch,Crystal A Kolden

doi:10.1088/1748-9326/11/4/045005

Abstract

Lightning-caused wildfires account for a majority of burned area across the western United States (US), yet lightning remains among the more unpredictable spatiotemporal aspects of the fire environment and a challenge for both modeling and managing fire activity. A data synthesis of cloud-to-ground lightning strikes, climate and fire data across the western US from 1992 to 2013 was conducted to better understand geographic variability in lightning-caused wildfire and the factors that influence interannual variability in lightning-caused wildfire at regional scales. Distinct geographic variability occurred in the proportion of fires and area burned attributed to lightning, with a majority of fires in the interior western US attributed to lightning. Lightning ignition efficiency was highest across the western portion of the region due to the concomitance of peak lightning frequency and annual nadir in fuel moisture in mid-to-late summer. For most regions the number of total and dry lightning strikes exhibited strong interannual correlation with the number of lightning-caused fires, yet were a poor predictor of area burned at regional scales. Commonality in climate–fire relationships for regional annual area burned by lightning- versus human-ignited fires suggests climate conditions, rather than lightning activity, are the predominant control of interannual variability in area burned by lightning-caused fire across much of the western US.

Highlights

Lightning is a significant contributor to area burned globally, a predominant contributor to area burned in sparsely populated areas such as boreal systems (e.g., Stocks et al 2002), and accounts for nearly two-thirds of burned area in the western United States (US) (e.g., Pyne et al 1996, Stephens 2005)
Lightning was the dominant source of wildfire in most mountainous regions, and contributed to most (>98%) of the area burned within portions of these ecoprovinces, across remote areas that may be of lower priority for suppression, more difficult to access, or have abundant fuel
While our study examined these relationships at broad ecoprovince scales, the conclusions are likely scaledependent as ignitions are hypothesized to be an increasingly important factor at smaller scales while climate variability explains less variance at smaller scales (e.g., Urbieta et al 2015)

Summary

Introduction

Lightning is a significant contributor to area burned globally, a predominant contributor to area burned in sparsely populated areas such as boreal systems (e.g., Stocks et al 2002), and accounts for nearly two-thirds of burned area in the western United States (US) (e.g., Pyne et al 1996, Stephens 2005). Unlike the more slowevolving and predictable environmental contributors to wildfire potential, such as fuel accumulation or drought, the stochastic nature of lightning presents a number of challenges both to fire management seeking to predict lightning-caused fire outbreaks, as well as to researchers seeking to model future wildfire activity under anthropogenic climate change. Regional outbreaks of lightning accompanied by inconsequential precipitation (i.e., dry lightning) that reach a receptive fuel bed can result in widespread concurrent ignitions that compromise fire suppression efforts (Rorig and Ferguson 2002). Lightning-ignited fires often occur in remote areas and are a natural biophysical process, they are often suppressed due to either secondary fire impacts, such as smoke-related degradation of regional air quality (e.g., McKenzie et al 2014), or due to concerns that fire growth will eventually threaten infrastructure. The unique risks to infrastructure and ecosystems posed by lightning highlights the need to identify and understand patterns of lightning-caused wildfire

Results

Discussion

Conclusion