Characterisation of thunderstorms that caused lightning-ignited wildfires

Abstract

This work studies the characteristics of thunderstorms that cause lightning-caused wildfires in Catalonia, north-east Iberian Peninsula, using lightning and weather radar data. Although thunderstorms produce ~57 000 cloud-to-ground (CG) flashes yearly in Catalonia, only 1 in 1000 end up as a flaming wildfire. Characterisation of thunderstorms that ignite wildland fires can help fire weather forecasters identify regions of increased ignition potential. Lightning data and radar products like maximum reflectivity, echo tops heights and equivalent liquid content were obtained over a 7-year period. Characteristics of thunderstorms that ignite wildfires are examined including storm motion, duration, morphology and intensity. It was found that most probable ignition candidates are lightning associated with cellular thunderstorms and non-linear systems. Radar reflectivity values for lightning that ignites wildfires were found to be below average, these morphological types favouring the occurrence of lightning outside regions of high reflectivity, where precipitation reaching the ground is low or non-existent. Thunderstorms that ignite wildfires are typically of low intensity, with a CG flash rate below average. Most ignitions occur during the maturity phase when the CG flash rate is the highest. A better scientific understanding of the thunderstorms that cause lightning wildfires will help improve early firefighting response.