Abstract
Spatial relationships between lightning-induced forest fires and topography, vegetation, climate and lightning characteristics were analyzed in the province of León (NW Spain). The study was based on reported lightning-induced forest fires in the period 2002-2007. A statistical model based on logistic regression was developed to estimate the probability of occurrence of a lightning-induced fire in a 3 x 3 km grid. The importance of accurate location of the ignition point was also investigated in order to evaluate the sensitivity of the model developed to uncertainty of the location. The model developed with accurate ignition point data showed a better predictive ability than the model constructed with all the ignition points available. The former model was therefore selected for long-term prediction of the occurrence of lightning-induced fires in the province. According to this model, the probability of a forest stand being affected by lightning-induced fire increased with decreasing altitude, and when there was a high proportion of coniferous species in the stand, a high percentage of lightning strikes in forest areas and a high number of dry storm days in the area. Although the model has not been validated, the results can be considered spatially robust because it shows good classification ability and the predicted spatial probability distribution is consistent with the observed historical fire records. The model will be useful in the spatially explicit assessment of fire risk, the planning and coordination of regional efforts to identify areas at greatest risk, and in designing long-term wildfire management strategies.
Highlights
Fire is the most serious threat to Spanish forests
The efficiency of individual lightning strikes in igniting a forest fire is affected by variation in lightning properties such as quantity, polarity and intensity; moisture properties of forest fuel resulting from recent weather conditions including precipitation, temperature and humidity; topographic variables that may affect the above-mentioned variables (e.g. Díaz-Ávalos et al, 2001), and rates of combustion, which vary with type of fuel
The particular period (2002-2007) was selected because: (i) 2002 was the first year that some wildfire ignition points were recorded in the province; (ii) it enables the assumption that land cover does not differ from that in 2003, the year for which land cover data was available for the present study; (iii) flash detection efficiency has improved greatly in Spain in recent years since the detection network began to operate in 1992
Summary
Lightning is the major natural cause of forest fire ignition in Spain and throughout the world (Pyne et al, 1996), and is the main overall cause of ignition in some areas, such as boreal forest. Human-induced fires are predominant in countries around the Mediterranean Basin and in other similar areas around the world (Vázquez and Moreno, 1998), and because of the importance of such fires in the current forest fire regimes of these countries, little attention has been given to lightning-induced fires. Lightning-ignited fires may burn larger areas of forest than human-induced fires because of their remoteness and aggregation in time and space (Podur et al, 2003). The relative importance of all these variables varies with the scale considered, and it is unrealistic to present a general model for large scales, making it advisable to develop models at local or regional scales (Pacheco et al, 2009)
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