The Role of Lightning and Environmental Conditions in Lightning-Ignited Wildfires in the Contiguous United States

Understanding how lightning interacts with environmental conditions to ignite wildfires is key to improving fire risk assessments. While previous studies have explored the role of lightning characteristics and environmental conditions in fire ignition on regional scales, a comprehensive analysis across the contiguous United States (CONUS) is lacking. This study investigates the influence of both lightning characteristics and environmental conditions on lightning-ignited wildfires from 2016 to 2020 using high-resolution lightning, precipitation, meteorological, and land cover datasets. By matching over 25,000 lightning-ignited wildfires (LIWs) to nearby lightning events, we distinguish between fire-initiating (FL) and non-fire lightning (NFL) and analyze key variables including lightning peak current, flash multiplicity, precipitation, fuel moisture, vapor pressure deficit, and vegetation type. Results show that fire lightning tends to have lower multiplicity and slightly higher peak current, and occurs under drier atmospheric and fuel moisture environments. Precipitation accumulated over 1 h and 24 h prior to LIWs shows the largest effect-size difference between FL and NFL, followed by fuel moisture and energy release component. Among vegetation types, evergreen needleleaf forests and grasslands show the highest relative ignition efficiency. Regional analysis across National Climate Assessment regions reveals notable variation in the relative importance of these factors, with eastern regions showing stronger sensitivity to precipitation and fuel moisture compared to western regions. We also find that holdover fires, discovered more than 24 h after ignition, occur under wetter conditions compared to promptly detected fires. These findings highlight the dominant role of environmental conditions in lightning fire ignition and emphasize the need for region-specific fire management strategies.