Assessing the Temporal Changes in Alpine Hillslopes Prone to Erosion

Steep mountain hillslopes are severely affected by natural hazards such as landslides and soil erosion. This study aimed to i) assess the temporal changes of degraded hillslopes over a decade interval (2012-2023) in the upper Cordevole catchment (eastern Italian Alps), and ii) investigate the development of hillslope erosion (rill formations) in an experimental hillslope located in a sub-catchment of the upper Cordevole. High resolution orthophoto images were used to analyze erosion-prone hillslopes change dynamics through a supervised classification using a random forest algorithm. In addition, photogrammetric data collected by an Unmanned Aerial Vehicle were used to reconstruct high-resolution Digital Surface Models (DSMs) of the experimental hillslope and determine the spatial eroded depth of the soil. In addition, monthly pictures acquired from June 2023 to May 2024 were used to investigate rill formation on the same hillslope. Past trends in the catchment show erosion-prone area expansion of ~31 ha/yr for slopes between 18° and 50°. During 2015-2023, the eroded hillslope Area 1 and Area 2 increased by 15% and 14%, with annual rates of change of 13 m2/yr and 6.5 m2/yr, respectively. The DSM analysis (comparison between August 2023 and April 2024) shows that the average depth of the soil removed along the rill networks was estimated as 5.2 cm (Area 1) and 2.9 cm (Area 2). These dynamics of erosion prone expansion on Italian Alps highlight the need for continuous monitoring of soil erosion and the implementation of mitigation strategies aiming at a restoration of vegetation on eroded hillslopes.