## 2 The Stage-Wise Methodology for the GHM Characterization of the Landslide Mechanisms
For the Pisciolo case study, the slope-atmosphere-vegetation interaction was simulated, first through hydraulic (H) uncoupled FEM modelling (Figure 9, [40,61]), inputting net rainfall rates at the top boundary of the slope model, calculated as the difference of the total rainfall rate and the evapo-transpiration rate estimated by means of the FAO-Penman-Monteith method [62]. This hydraulic modelling, combined with the limit equilibrium analyses (Stage II), confirmed that seasonal slope-vegetation-atmosphere interaction lead to F = 1 by the end of winter/early spring in bodies deeper than 3 m [63,64,65,63]. At the same time, the analyses showed that the stability of landslide  
Figure 7: Geomorphological map (**a**) and section (**b**) of the Tolve slope (adapted from [60]); Key. Soil complexes: yellow sands (**A**), remoulded clays (**B**), sub-Apennine Clays (**C**), weathered clays (**D**). bodies shallower than 1-2 m is connected to the intensity and duration of single rainfall events, or to their short-term sequences from mid-autumn to mid-spring ([61]; Figure 9). The research results, therefore, highlight the variability with depth of climatic variables, which the landslide body stability relates to in clay slopes similar to the Pisciolo slope. [PERSON] [66], [PERSON] [64] and [PERSON] [67] also reported the results of stage III analyses of the Pisciolo slope, carried out using fully coupled hydro-mechanical (HM) FEM modelling of the slope-vegetation-atmosphere interactions. [PERSON] and [PERSON] [67] reported two-dimensional coupled HM numerical analyses of the slope-vegetation-atmosphere interaction, but assumed the slope to be homogeneous and checked the influence of the model initialization procedure on the prediction of the slope-vegetation-atmosphere interaction. The authors concluded that only when the slope model initialization accounted for the slope loading history, including that determined by the excavation of the river valley and the consequent formation of the slope, could the numerical analyses predict that even a homogeneous slope formed by an elasto-plastic, non hardening clay may become location of a climate driven landslide. For the Tolve slope, [PERSON] et al. [60; 41] diagnosed the landslide mechanism determined through a small size excavation at the slope toe using a stage-wise methodology. Temporal geomorphological analyses [68] allowed them to recognize that the slope is part of a large paleo-landslide basin, having its original toe at the Castagno River, at the foot of the valley (Figure 7). Given the study of the slope stratigraphy, showing that the slope is mainly formed from sub-Apennine stiff clays, and the monitoring of the deep displacements (through inclinometers) and of the piezometric head, the authors recognized that the current landslide largely represents a reactivation of sliding, rather than the effect of a first failure process. In this slope, the first failure of the clays took place after excavation only in a limited region, where a new shear band developed, linking the bottom of the excavation with the pre-existing shear band at depth. Given this phenomenological interpretation of the landslide mechanism achieved through stage I studies, both the stage II and III analyses confirmed how a small excavation along the longitudinal axis of a paleo-landslide body can to trigger the delayed reactivation of large portions of part of this body, due to the new yielding of the slope clay triggered by the excavation, which starts at the floor and develops progressively over time until the original shear band lying at depth is reached. As a consequence, the new landslide activity is characterized by mass movements whose size and direction differ from those of pre-existing landslides. A stage III FEM analysis of the slope processes predicted the reactivation of sliding at Tolve after the completion of consolidation pos-excavation once a pre-existing shear band, which includes clay weaker than the undisturbed stiff clay, is implemented in the model [60; 41].