Characteristics of lightning related to wildfire ignitions in Catalonia

Abstract

What are the characteristics of lightning that influence the probability that an individual stroke will ignite a wildfire? It is generally accepted that long continuing current following some return strokes is the cause of ignition in forest fuels. However, because these low-level currents are not detectable with operative Lightning Location Systems, other lightning characteristics correlating with its occurrence have been proposed and used to estimate ignition probability. These variables are typically: flash multiplicity, stroke polarity, stroke peak current and flash interstroke interval. The region of Catalonia is prone to forest fires, and to set a probability of ignition to each cloud-to-ground flash could be useful in wildfire management. A set of more than 500 lightning-ignited wildfires that occurred in Catalonia between 2004 and 2009 was analyzed, in order to find which flash/stroke characteristics are related to ignition. Lightning activity was gathered by the Lightning Location System of the Meteorological Service of Catalonia. Lightning related to these wildfires were selected from the lightning database using a proximity index. The statistical analysis has shown that the sample of lightning causing ignition does not present any characteristic that differentiates it from the overall population. Polarity percents, multiplicity and peak current frequency distributions in the lightning causing ignition set are similar to the climatological ones. Besides this analysis, a high-speed video field campaign of natural lightning recordings was conducted, to obtain new insight into the characteristics of lightning bearing a continuing current. Video analysis has shown that almost each kind of cloud‐to‐ground (CG) flash (negative, positive, single or multiple stroke) can have a continuing current component. Only negative strokes with peak currents above 20 kA were not followed by long continuing current. These results are similar to studies carried out in other regions.