Fire-climate history and landscape patterns of high burn severity areas on the California southern and central coast

Abstract

There is mounting evidence that fire size and severity have been growing on the central and southern California coastal landscape over the past several decades. Landsat satellite data was analyzed for the 20 largest fires on the Central California coast since 1984 to determine the relationships between climate/weather conditions at the time of ignition and the size of high burn severity (HBS) areas. The study also examined the relationship between area burned and landscape patterns of HBS coverage, including patch size, edge complexity, perimeter-to-area ratio, and aggregation metrics. Results showed that climate conditions at the time of ignitions have been significant controllers of the total area of HBS and the complexity of HBS patches on the fire landscape. As maximum air temperatures for the month of ignition approached 40o C, the percentage of HBS to total area burned frequently exceeded 20%. The percentage of HBS to total area burned also exceed 20% when the precipitation total recorded during the previous 12 months was less than 25% of the annual average precipitation. Landscape analysis results showed that, as the total area burned in fires on the Central California coast grows, the edge lengths and areas of HBS patches also grows at a rapid rate. At the same time, the perimeter-to-area ratio of HBS patches decreases gradually and the HBS patches become more aggregated as total burned area grows.