Reassessing wildfire susceptibility and hazard for mainland Portugal

Abstract

Recent large wildfires have caused serious environmental and social impacts in different areas of the world, such as Portugal, Greece and Australia. Sociodemographic changes in rural areas and climate change issues create unprecedented and challenging circumstances that call for an adjustment of fire management strategies and planning tools. In this research, we revise the procedure to assess wildfire susceptibility and hazard for mainland Portugal in a structural perspective. Based on a dataset of burned areas covering 44 years and a set of predisposing factors related to topography and landcover, we tested several susceptibility models using the Likelihood Ratio method, to calculate favourability scores. Landcover classes were analysed using national detailed sources and considering different timeframes. Hazard levels were obtained by combining the susceptibility model with the best accuracy and the probability to burn estimated from fire history (1975–2018). The resulting hazard values were classified in 5 levels based on the breaks of the success curve, instead of quantiles as in previous maps, to ensure territorial continuity at different spatial scales. The results show where the combination of terrain features is more favorable to fire propagation. The higher favourability scores were found for shrubland-type vegetation, whereas agricultural areas, cork and holm forests show lower scores. Eucalyptus and maritime pine forests show similar intermediate scores and have increased since 2007. The two highest hazard classes classify correctly 90% of the burned area over 44 years, demonstrating the high accuracy of the model. If integrated in spatial planning instruments, in conjunction with municipal plans, the two most hazardous classes may hinder the expansion of built-up areas. About 2% of the municipalities have more than 90% of their territory classified as hazardous, whereas 32% of the municipalities have, instead, less than 10% of hazardous area. These structural maps are a useful baseline for a long-term approach and can be complemented by estimations regarding the behavior and severity of wildfires, which should be further explored.