Fire regime dynamics in mainland Spain. Part 1: Drivers of change

Fire regimes are evolving worldwide driven by socioeconomic and environmental changes. Understanding the forces behind fire regime dynamics is essential to achieve effective wildfire management and policymaking. The current research belongs to a series of two manuscripts aimed at describing spatial-temporal dynamics of fire regime and its drivers in mainland Spain. In this work, we identified the main transitional pathways of fire regime zones between past (1974-1994) and current (1995-2015) conditions to identify the influence of the main wildfire drivers (demographic potential, climate trends, forest interfaces and topography). Our methodology combined Principal Component Analysis and Ward's hierarchical clustering to identify and spatialize homogenous regions of fire regime on the basis of the main fire regime features: number of fires, burned area, burnt area from lightning-caused fires, area affected by large fires (>100 ha) and seasonality. This procedure was replicated in current and past conditions to extract the most frequent combinations of fire regime typologies, eventually leading to a set of binary response variables (change versus persistence of fire regime). Finally, Random Forest regression was applied to estimate the explanatory performance of fire regime drivers for each transition path. Our results point to an overall decline in fire activity over most of the Spanish territory. The hinterlands and Mediterranean coast experienced the greatest decrease in fire activity. In contrast, winter activity has progressed in the North-western region. According to Random Forest outputs, demographic potential highlights as the main driver of fire regime change (both regressive and progressive), followed by climate dynamics (temperature and rainfall trends) and topographic features. In turn, Wildland-Agricultural Interface (WAI) and Wildland-Urban Interface (WUI) were also behind several noticeable trajectories as is the case of winter fire progression (WAI) or moderate increase in fire incidence linked to human-caused fires (WUI). (C) 2019 Elsevier B.V. All rights reserved.