C. Vennari

Catalogue of Rainfall Events with Shallow Landslides and New Rainfall Thresholds in Italy

In Italy, rainfall-induced shallow landslides are frequent and harmful phenomena. The prediction of their occurrence is of social significance for civil protection purposes. For the operational prediction of rainfall-induced shallow landslides empirical rainfall thresholds based on the statistical analysis of past rainfall conditions that triggered slope failures are commonly used. The paper describes a catalogue of 1981 rainfall events, which caused 2408 shallow landslides in Italy in the period 1996–2012. Information on rainfall-induced landslides was collected searching chiefly online newspaper archives, blogs, and fire brigade reports. For each documented failure, we reconstructed the triggering rainfall conditions (rainfall duration D and cumulated rainfall E) using national and regional rain gauge networks. We analysed the rainfall conditions to determine new ED rainfall thresholds for Italy. The calculated thresholds can be implemented in a landslide forecasting system to mitigate landslide hazard and risk.

Rainfall Thresholds for Possible Occurrence of Shallow Landslides and Debris Flows in Italy

In mountain regions worldwide, rainfall-induced landslides and associated debris flows erode slopes, scour channels, and contribute to the formation of alluvial fans that may harm humans and destroy buildings. Rainfall-induced slope failures are frequent and widespread in Italy, where individual rainfall events can result in single or multiple slope failures in small areas or in very large regions. Most of the harmful failures were rainfall-induced, and several were shallow slides or debris flows. In the 60-year period 1950–2009, casualties due to landslides were at least 6,349, an average of 16 harmful events per annum. The large number of harmful events indicates the considerable risk posed by rainfall-induced shallow landslides and debris flows to the population of Italy (Guzzetti et al. 2005a; Salvati et al. 2010).

The “Piano dell’Acqua” sinkholes (San Basile, Northern Calabria, Italy)

The occurrence of sinkholes not directly related to karst has been determined in several areas worldwide in recent years. These phenomena may be particularly dangerous to humans and infrastructure due to their subtle origin and need to be carefully examined. In this work, we describe five sinkholes recently identified in a hilly setting of Southern Italy characterized by Pliocene conglomerate and sand, and variously dislocated by tectonic structures. The sinkholes were examined by different methods (interpretation of multi-temporal aerial photos, geological, geomorphological and geophysical surveys). An historical analysis was performed to collect and critically evaluate information regarding the age of the phenomena. Based on this information, it can be conjectured that two of the five sinkholes developed during the 2000–2001 winter; two of the remaining probably originated during the 70s; the last one opened sometime between February 2001 and November 2007. Based on such chronology, attempts have been performed to identify the likely triggers, through hydrological and seismic analyses. In both cases, no immediate correlation could be found. The origin of the studied phenomena remains uncertain, and may be related to sub-cutaneous erosion, in an area that is renowned to be rich in groundwater. Local changes in the water table, related to climate and/or man-induced activities, may have triggered the development of the cover suffusion-type sinkholes. The present work highlights the potential for this type of phenomena to occur in geological settings without the direct presence of soluble rocks at the surface, a condition quite common in Southern Italy, and the need to carry out further studies in order to better comprehend their mechanisms of origin and successive evolution, and to properly evaluate the related hazard.

Data collection for reconstructing empirical rainfall thresholds for shallow landslides: challenges and improvements in the Daunia Sub-Apennine (Southern Italy)

Il presente lavoro illustra i risultati ottenuti nella raccolta di informazioni relative ad eventi franosi pluvio-indotti, utili ad una successiva definizione di soglie pluviometriche preliminari per il possibile innesco di frane superficiali nellarea del Sub-Appennino Dauno (Puglia settentrionale). Lattivita di raccolta dati e stata realizzata in collaborazione tra lIstituto di Ricerca per la Protezione Idrogeologica (CNR-IRPI) e il Centro Funzionale Decentrato del Servizio Protezione Civile della Regione Puglia.Nel presente contributo verranno messe in evidenza le difficolta nella creazione del catalogo delle frane pluvio-indotte nel Sub-Appennino Dauno, e si presenteranno gli aggiornamenti sulla banca-dati sinora disponibile, utile al fine di definire una soglia di pioggia che, se raggiunta o superata, puo causare linnesco di frane.La ricostruzione di una soglia pluviometrica per linnesco di fenomeni franosi e la sua integrazione in un sistema dallertamento nazionale puo essere molto utile a fini operativi, ed e pertanto uno degli obiettivi primari da raggiungere per una ottimale gestione del territorio in riferimento a eventi di dissesto idrogeologico.