Lightning‐Ignited Wildfires in the Western United States: Ignition Precipitation and Associated Environmental Conditions

Abstract

Cloud‐to‐ground lightning with minimal rainfall (“dry” lightning) is a major wildfire ignition source in the western United States (WUS). Although dry lightning is commonly defined as occurring with <2.5 mm of daily‐accumulated precipitation, a rigorous quantification of precipitation amounts concurrent with lightning‐ignited wildfires (LIWs) is lacking. We combine wildfire, lightning and precipitation data sets to quantify these ignition precipitation amounts across ecoprovinces of the WUS. The median precipitation for all LIWs is 2.8 mm but varies with vegetation and fire characteristics. “Holdover” fires not detected until 2–5 days following ignition occur with significantly higher precipitation (5.1 mm) compared to fires detected promptly after ignition (2.5 mm), and with cooler and wetter environmental conditions. Further, there is substantial variation in precipitation associated with promptly‐detected (1.7–4.6 mm) and holdover (3.0–7.7 mm) fires across ecoprovinces. Consequently, the widely‐used 2.5 mm threshold does not fully capture lightning ignition risk and incorporating ecoprovince‐specific precipitation amounts would better inform WUS wildfire prediction and management.

Simulated Future Shifts in Wildfire Regimes in Moist Forests of Pacific Northwest, USA

“…Coupling vegetation change and management scenarios with fire simulation models is an important next step for future research. Additionally, we acknowledge several other interrelated environmental factors that could influence future fire regime change in unexpected ways in the future: changes in anthropogenic ignitions (Balch et al., 2017), lightning ignitions (Kalashnikov et al., 2023), microclimate conditions such as wind and solar radiation (De Frenne et al., 2021), and fire suppression and fuel treatment strategies (Pritchard et al., 2021).…”