The influence of climate, population density, tree species and land cover on fire pattern in mainland Portugal

Abstract: Forest fires in mainland Portugal are becoming more extreme, resulting in increasingly larger burnt areas and tragic human fatalities, as was shown by the 2017 fires. Research shows that there are many natural factors contributing to such fire vulnerability conditions, such as climate, fuel continuity, forest structure, tree species types, amongst others, that are intertwined with anthropic factors than can intensity the fire vulnerability. This study focusses on the investigation of how some of these factors (namely Fire Weather Index, population density, tree species and land cover) influence forest fire resulting burnt area between the years of 1980 to 2019. Supported by other similar studies focusing on the impact of given variables on forest fire burnt area, a GIS grid-based analysis was made for the burnt area for mainland Portugal, for the period of study, where a variety of statistical techniques were applied to understand its relation (from more basic correlation between variables, to a characteristic fire size (CFS) applied to distinct variables). This research showed that Eucalyptus globulus is related with bigger burnt areas, as well as leading to bigger CFS, when compared with Pinus pinaster and Quercus suber; agro-forested land cover areas seem to be less fire prone than forested land cover areas; Fire Weather Index (FWI) has an important impact on the CFS, and decadal CFS has dramatically increased since 1980 to 2019. The results suggest that forest management in agro-forested areas dramatically reduces both the total burnt area as well as the CFS. There is a strong correlation between these areas and the presence of Quercus suber, which may indicate that this combination is less vulnerable to fire.