Abstract. In the framework of landslide risk management, it appears relevant to assess, both in space and in time, the triggering of rainfall-induced shallow landslides, in order to prevent damages due to these kind of disasters. In this context, the use of real-time landslide early warning systems has been attracting more and more attention from the scientific community. This paper deals with the application, on a regional scale, of two physically-based stability models: SLIP (Shallow Landslides Instability Prediction) and TRIGRS (Transient Rainfall Infiltration and Grid-based Regional Slope-stability analysis). A back analysis of some recent case-histories of soil slips which occurred in the territory of the central Emilian Apennine, Emilia Romagna Region (Northern Italy) is carried out and the main results are shown. The study area is described from geological and climatic viewpoints. The acquisition of geospatial information regarding the topography, the soil properties and the local landslide inventory is also explained.The paper outlines the main features of the SLIP model and the basic assumptions of TRIGRS. Particular attention is devoted to the discussion of the input data, which have been stored and managed through a Geographic Information System (GIS) platform. Results of the SLIP model on a regional scale, over a one year time interval, are finally presented. The results predicted by the SLIP model are analysed both in terms of safety factor (F s ) maps, corresponding to particular rainfall events, and in terms of time-varying percentage of unstable areas over the considered time interval. The paper compares observed landslide localizations with those predicted by the SLIP model. A further quantitative comparison between SLIP and TRIGRS, both applied to the Correspondence to: R. Valentino (roberto.valentino@unipr.it) most important event occurred during the analysed period, is presented. The limits of the SLIP model, mainly due to some restrictions of simplifying the physically based relationships, are analysed in detail. Although an improvement, in terms of spatial accuracy, is needed, thanks to the fast calculation and the satisfactory temporal prediction of landslides, the SLIP model applied on the study area shows certain potential as a landslides forecasting tool on a regional scale.

The article relates the main findings of a recent investigation aimed at modeling the triggering of shallow landslides. A simplified model for assessing the safety factor of potentially unstable slopes, directly related with rainfall trends, was developed. Based on the geometric characteristics of the slope, the geotechnical properties, and strength parameters of the soil, the model makes it possible to define a safety factor of a slope as a function of time. The model is based on the limit equilibrium method and takes into account the seepage of underground water. The safety factor is, in turn, related to the seasonal rainfall. The model was applied on a local scale to some historical cases which had occurred recently in Northern Italy. The paper shows how the results of the application of the model on a local scale achieve a good agreement between the instability condition and the real date of each considered event.

On April 10-11, 2005, the Emilia Romagna Apennine was affected by an intense rainfall event that triggered dozens of soil slips in the Province of Reggio Emilia. These shallow landslides occurred mainly on slopes of cultivated lands, often blocking roads, causing damages to crops and economic loss. Based on the analysis of an inventory of aerial photographs, it was possible to locate 45 sites where soil slips have occurred. In this paper, the area of study is described from a geological and climatic point of view. The authors analyze both the predisposing factors, related to the morphology of the territory, and the phenomena triggering factors, related to the rain trend. Once the geometrical features and characteristics of the soil slopes were available, a physically based triggering model, recently developed by the authors, was locally applied at each site. The model, which is based on the limit equilibrium method and on the hypothesis of infinite slope, is briefly described. It assumes a partial saturation condition of the soil and provides the safety factor of each slope as a function of time-variable rainfall intensity. The choice of the input parameters of the model is explained in detail. It is underlined, in particular, how the only parameter that has been determined through a procedure of back analysis, i.e., the discharge capability, is comparable to the typical permeability values obtained through field measurements by other authors, for similar kinds of soils and conditions. In this article, the results of the application of our model to the study areas, within a three-year time frame, are presented. Furthermore, on the basis of the analysis carried out, some observations on the operating mode of the model are carried out and its ability to predict a phenomenon triggering is evaluated.

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