Spatial, Temporal and Electrical Characteristics of Lightning in Reported Lightning-Initiated Wildfire Events

Abstract

Analysis was performed to determine whether a lightning flash could be associated with every reported lightning-initiated wildfire that grew to at least 4 km2. In total, 905 lightning-initiated wildfires within the Continental United States (CONUS) between 2012 and 2015 were analyzed. Fixed and fire radius search methods showed that 81–88% of wildfires had a corresponding lightning flash within a 14 day period prior to the report date. The two methods showed that 52–60% of lightning-initiated wildfires were reported on the same day as the closest lightning flash. The fire radius method indicated the most promising spatial results, where the median distance between the closest lightning and the wildfire start location was 0.83 km, followed by a 75th percentile of 1.6 km and a 95th percentile of 5.86 km. Ninety percent of the closest lightning flashes to wildfires were negative polarity. Maximum flash densities were less than 0.41 flashes km2 for the 24 h period at the fire start location. The majority of lightning-initiated holdover events were observed in the Western CONUS, with a peak density in north-central Idaho. A twelve day holdover event in New Mexico was also discussed, outlining the opportunities and limitations of using lightning data to characterize wildfires.

Flash Characteristics and Precipitation Metrics of Western U.S. Lightning-Initiated Wildfires from 2017

“…Of these 122 events, 25 were excluded due to the inability to find either a flash or stroke that caused the fire within 2 km of the fire start location and 10 days from the report date. These exclusions may be due to the lightning occurring outside of the 2 km radius used to associate lightning to the wildfire, an incorrect classification of the cause of initiation (human instead of lightning-initiated), or they may be long duration holdover events that are beyond the 10 days used in this study as shown in the previous study by Schultz et al [12]. In reference to NLDN data, the 95th percentile lightning distance is a 5 km median error, with the 75th percentile being~1.6 km [42].…”

“…A backward search from the reported event time was performed in this area to determine the closest lightning flash within 2 km of the start location, similar to the study by Nauslar [39]. This search of lightning data extended back as far as 10 days because 48% of LIWs have been observed to be holdover events [12] that occur when fuels ignited by lightning smolder for days or even weeks before they intensify into a detectable fire [15,22].…”

“…Thus, +CG flashes are thought to be responsible for most natural wildfires [3,6,10,11]. However, recent research indicates that 90% of lightning-initiated wildfires between 2012 and 2015 were ignited by -CG flashes [12].…”

Examining the Sustainability of Tropical Island Forests: Advances and Challenges in Measurement, Monitoring, and Reporting in the U.S. Caribbean and Pacific

“…Forest land clearance was a widespread and significant disturbance during colonization of many of the islands, as discussed above, and continues to occur, albeit on a greatly reduced scale, mostly for development [32][33][34]38,[43][44][45][46]. Fire occurs naturally on islands with active volcanoes, but fire from lightning strikes is rare [91,92]. Apart from lava ignitions, most fire affecting the islands' forests is anthropogenic and has increased since human settlement and subsequent population expansion, particularly in the western Pacific, where it occurs in non-native and novel grasslands and along forest edges, and in dry areas of Hawaii and of southern and western Puerto Rico [91,92].…”

“…Fire occurs naturally on islands with active volcanoes, but fire from lightning strikes is rare [91,92]. Apart from lava ignitions, most fire affecting the islands' forests is anthropogenic and has increased since human settlement and subsequent population expansion, particularly in the western Pacific, where it occurs in non-native and novel grasslands and along forest edges, and in dry areas of Hawaii and of southern and western Puerto Rico [91,92]. Storms, including hurricanes (in the Caribbean) and typhoons (west of the international dateline) are a regular phenomenon in the tropics and range in their strength and frequency and in their effects on the islands' forests from one point or period of time to another.…”