Identifying geographical patterns of wildfire orientation: A watershed-based analysis

We searched for geographical patterns in the orientation of wildfires, using watersheds as spatial support for the analysis. An 1975–2005 annual fire atlas of mainland Portugal was used to compute the orientation of fire perimeters and watersheds, using principal component analysis. Circular statistics were employed to test for the existence of a preferred, as opposed to random, mean fire orientation in each watershed, and to search for evidence of orographic channelling of fire by comparing fire orientation and watershed orientation. We also tested for differences in fire orientation patterns under conditions of mild versus severe fire weather. Our findings show that in the 31 year period of the study, 84% of the overall area burned is accounted for by watersheds where fires display preferential orientation. Twelve of 102 watersheds display evidence of alignment between fire and watershed orientation and we found no distinction in fire orientation as response to fire weather. The spatial arrangement of watersheds where fires present similar orientation suggests wind as a major driver of the broader patterns found in this study. Results from this analysis ought to be relevant for supporting the delineation of landscape-scale fuelbreaks.

► We computed wildfire orientation for all fires in Portugal from 1975 to 2005.
► At watershed level, we assessed the existence of a preferred fire orientation.
► We found that 84% of the burned area shows preferential geographical orientation.
► Spatial pattern of preferred orientation suggests synoptic wind as key driver.