Spatial stratification of wildfire drivers towards enhanced definition of large-fire regime zoning and fire seasons

The area affected by wildfires is experiencing an overall decrease in the Mediterranean European region. However, there is no clear trend associated to the incidence of large fire events, which continue to pose an important threat to assets-at-risk, while debates on control by meteorological or fuel drivers are ongoing. Understanding the underlying spatial and temporal patterns of large-fire drivers is of critical importance for a more efficient and science-based management, and specifically for improving wildfire season definition and informing fuel management. Taking advantage of the reliable wildfire data available in Spain, we analyzed large fires (>100 ha) in the period 2010-2015 to outline homogenous spatial-temporal regions in terms of the influence of the main drivers of large-fire activity: temperature, wind speed, slope, distance to populated places and roads, and proximity to agricultural lands. We combined Geographically Weighted Logit Regression (GWLR) models to parameterize the marginal influence of the drivers, with optimized hierarchical clustering to define uniform regions in terms of the underlying driving factors. These regions were subsequently analyzed for monthly distribution of fire occurrence and associated fuel models. We identified four different zones in terms of drivers' features, capturing dissimilar intra-annual patterns of fire activity and affected fuels: one covering the Mediterranean and two along the northern coast, and a fourth aggregation in the hinterlands that seems to act as transition area. The Mediterranean and hinterland were linked to weather-related summer ignitions, late and early summer respectively. The northern cluster gathers most winter fires starting in remote locations under steep slopes and strong wind conditions. The northwestern cluster accounts for most of the fire activity in Spain, related to complex relief and shrub-type fuels.