A multi-hazard map-based wildfires and gully erosion in a Mediterranean mountain environment

One region may suffer from more than one natural hazard. Wildfires and gully erosion are common in a Mediterranean mountain environment, as well as in the Portuguese mountains. In this context, integrated assessments of multi-hazards, especially related with wildfires and gully erosion are needed for more efficient land management. The main aim of this study is producing a multi-hazard map that helps the planners to identify priority action areas to implement hazard mitigation and disaster management measures. The study area is located in the Alva river basin, in the mountainous area of central Portugal, which is frequently affected by wildfires and also by gully erosion. The follow objectives were performed to achieve the main aim: i) to draw up a wildfire hazard map for the studied area; ii) to identify, map and characterise the areas affected by gully erosion; iii) to analyse the main geo-environmental factors that control gully distribution based on frequency ratio (FR) model and Maximum Entropy (MaxEnt) method; iv) to draw up a gully erosion hazard maps based on FR and MaxEnt method and assess the accuracy of the two models; v) produce a multi-hazard map where priority areas for intervention are identified, both in terms of wildfires and gully erosion. The wildfire hazard map was based on the methodology of the Institute for Nature Conservation and Forests (ICNF) (ICNF (2020). Metodologia para a produção da Carta de Perigosidade de Incêndio Rural de cariz estrutural. Relatório definitivo, Lisboa, p. 7.). Gully erosion inventory map was prepared using orthophoto maps and a total of 38 gullies were identified. The hazard maps of gully erosion were developed by applying FR and MaxEnt methods considering a set of 13 geo-environmental factors (such as altitude, slope, curvature, aspect, flow accumulation, terrain ruggedness index, land use, road distance, and burn severity). The overall success rate of AUC of 68.7 and 70.4% were obtained for FR and MaxEnt model, respectively. Finally, the wildfire hazard map and the gully hazard map were used to produce the multi-hazard map (MHM). The MHM places around 36% of the study area in areas of moderate hazard, while more than half of the study area is in areas of high and very high hazard. This confirms the high hazard to wildfires and the favourable conditions for gully erosion. The results show the importance and usefulness of using multi-risk methodologies, in particular the combination of the GHM (gully hazard map) and WHM (wildfire hazard map) for more effective soil conservation management in areas affected by wildfires.