BC Wildfire PSTA Lightning Fire Density

Provincial Strategic Threat Analysis (PSTA) is designed to consistently assess and map potential wildfire threats to values across the landscape (including communities, infrastructure and natural resources) and to integrate different aspects of wildfire hazard and risk.

The lightning caused fire density layer was analyzed using lightning caused fires with final sizes greater than 4.0 ha for the last 67 years (1950-2016). These were given a weight of one (1) in the analysis, while large fires (> 500 ha) were given a weight of 5, in order to reflect the much greater cost and damage usually associated with larger fires. A kernel density analysis was conducted to represent the historic fire data as a seamless surface representing fire occurrence across the province; a 10 km search radius was chosen, and the pixel size was 50 m. The ArcGIS kernel density function fits a smooth surface to a spatial point frequency dataset, representing actual fire origin points as random samples from a smooth probability surface. The analysis search radius was 10 kilometers and this distance was reflected in the mapped output classes; thus, the fire density at any point on the landscape is a modeled probability value reflecting the number of historic fires found within a radius of 10 kilometers, or within a 314 km2 circle around the point of interest. Note that this is different from a simple point density, and the values in the fire density layer classes do not represent the exact numbers of historic fires within the search radius; closer and more clustered fires are weighted higher within that circle, and this can result in significantly higher values than may be expected compared with a simple point search.The output values therefore represent a modeled probability approximately representing the number of nearby fires (4 ha and greater, treating 500+ ha fires as 5 individual events) since 1950. Using this as an input to the Wildfire Threat Analysis layer is based on the premise that areas that were prone to multiple larger fires in the past are likely prone to larger fires in the present and near future. Final class limits are based on the weighting scheme described above: fires from 0 to 4 ha (not counted, weight of 0); fires from 4.001 to 500 ha (weight of 1); fires 500.001 ha or larger (weight of 5). Units are approximate weighted fire frequency within a 10 km radius, 1950-2016. Water bodies were overlaid on the raster and assigned their own class, -1.