Monitoring the temporal evolution of a Sicilian badland area by unmanned aerial vehicles

Badlands are extremely fragmented landforms characterized by soil erosion processes at a short-time scale. In this paper, the annual evolution of hillslope morphological characteristics and erosion/deposition processes in a Sicilian badland area, surveyed on May 2021 and April 2022 by Unmanned Aerial Vehicles (UAVs), was investigated. Three-dimensional (3D) and planimetric (2D) approaches were applied to determine the badland morphometric characteristics. UAV surveys and photogrammetric 3D-model generation allowed for obtaining the digital terrain model and identifying the badland unit. The convergence index method was applied to evaluate the drainage network and its variation due to the erosion processes. The analysis highlighted a decrease of the morphometric indexes with increasing slope, which can be explained by the fact that the drainage network tends to be less tortuous and branched as slopes become steeper. The geomorphic change analysis showed that the soil erosion is evenly distributed along the badland slopes, while it is negligible along the drainage networks. The geomorphic changes due to slope collapses and soil erosion and deposition phenomena lead to a modification of the morphological characteristics of the badland unit, sub-units and the corresponding drainage networks. The results confirmed that badlands are intense erosion spots, with soil loss (approximately 348 t ha⁻¹ y⁻¹) much higher than the soil loss tolerance. Finally, the morphometric indexes were positively related to the sediment yield values, suggesting that in more extended and branched drainage networks sediment transport is more efficient.