Large-area analysis of soil erosion and landslides induced by rainfall: A case of unsaturated shallow deposits

Unsaturated shallow soil deposits may be affected by either superficial soil erosion or shallow landslides in adjacent or overlapping source areas and in different seasons when a different soil suction exists. The triggering analysis of both these processes is a relevant issue for the hazard analysis while the literature mostly provides specific approaches for erosion or for landslides. The paper proposes a large-area analysis for a case study of Southern Italy, consisting of unsaturated shallow deposits of loose pyroclastic (air-fall) volcanic soils that have been repeatedly affected by erosion and landslides in special seasons. For a past catastrophic event, the simulated source areas of shallow landslides are smaller than those observed in the field while the simulated eroded areas with thickness greater than 5 cm are comparable with the in-situ evidences, if the analysis takes into account high rainfall intensity and a spatially variable soil cover use. More in general, the results of the paper are consistent with the previous literature and also provide a methodological contribution about the application of distinct tools over large area. The added value is that the paper shows how the combination of distinct large-area analyses may help with understanding the dominant slope instability mechanisms. Only once this goal is fully achieved, can specific physically-based analyses be confidently performed at detailed scales and for smaller specific areas.