Abstract ID: 3.12999 | Accepted as Poster | Requested as: Talk | TBA | TBA

The management of torrential areas extends beyond the regulation of riverbeds and erosion hotspots; it encompasses the management of the entire catchment area, with spatial planning playing an important role. As the upper reaches of Slovenian torrential catchments are predominantly forested, close-to-nature forest management is of utmost importance to minimise torrential and erosion risks and reduce vulnerability to water-induced hazards. The strategic development and management of forest stands in torrential areas to improve and optimise their protective effect is essential for reducing flood damage throughout the Alps. Close-to-nature forest management in Slovenia is a best practice example for the implementation of a nature-based solution (NBS) for disaster risk reduction (DRR). There is limited knowledge on the protective effect of forests in torrential area for reducing cascading landslide risks during extreme rainfall events. The main objective of our study is to analyse the protective effect of forests on landslide occurrence by comparing landslides in forested and agricultural land. This study presents results based on remote sensing data collected before and after the extreme rainfall in August 2023. The analysis included 718 landslides, of which 260 occurred in forests, 182 on agricultural land and 276 landslides that occurred both land uses. The analyses reveal that forests play a crucial role in reducing the negative cascading effects associated with triggering landslides and mass movements in areas with torrential water formation, concentration and runoff. Due to the protective effect of forests and targeted forest management, the average density of (shallow) landslides in forests (22.4 km-2) is lower than in agricultural land, e.g. pastures and meadows (33.2 km-2). Landslides in forest areas occur on steeper slopes than landslides in agricultural areas; the average slope of landslides in forest and agricultural areas was 33.5° and 23.7°, respectively. Landslides in agricultural land move further; the average L/H ratio (length to distance ratio) for landslides in agricultural and forest areas was 2.6 and 1.6, respectively. Our research also confirms that forests significantly reduce the inflow of sediment and debris during torrential floods. This is further evidence of the protective effect of forests in torrential areas in reducing the overall flood risk.