The rainfall factor in lightning-ignited wildfires in Catalonia

Wildland fires originated by lightning in Catalonia (NE Spain) are systematically examined through the use of lightning and precipitation data. The region of study, with a Mediterranean climate, is prone to summer wildfires. Despite being mainly anthropogenic, lightning-ignited fires (10%) are relevant as they can trigger large fires. Given that the lightning efficiency in Catalonia is of 1/1400 fires per lightning, the ability to identify potential ignition candidates among the whole lightning population would be of great value to forest protection agencies. Literature reveals that lightning characteristics such as polarity or multiplicity has proven to be of limited value as predictors. Therefore, another approach is necessary to set a probability of wildfire ignition to each lightning. In this regard, the aim of this study was to explore the relationship between lightning-ignited wildfires and precipitation, as lightning-ignited wildfires in the region are often attributed to 'dry' lightning (lightning accompanied with little or no precipitation). Results revealed that 25% of the lightning strokes related to wildfire ignitions had no associated precipitation at all, 40% had less than 2 mm of precipitation and 90% had less than 10 mm. Results also revealed that holdover fires (ignitions with delayed arrivals) are rare in the region. Finally, results suggest that there is no apparent link between the amount of precipitation and the holdover duration, indicating that the survival phase of lightning-ignitions is mainly driven by the daily cycle of solar heating. All in all, adding information on the precipitation associated to each lightning may help focusing attention on a reduced sample of strokes and provide fire managers with valuable information about potential lightning-caused wildfires.