Metodologie di analisi e definizione di soglie di eventi pluviometrici che hanno innescato colate rapide e frane superficiali in un'area dell'arco alpino nord-orientale

Debris flows and shallow landslides, due to the high velocity, in recent decades have caused the most damage in Italy both in terms of casualties that economic losses. The triggering is in almost all cases related to intense rainfall events. For these types of landslides one of the main risk mitigation measures is the adoption of early warning systems based on rainfall thresholds that identify the critical amount of precipitation for landslide initiation. The aim of this research is the development of objective, repeatable and exportable methodologies for the identification, analysis and characterization of rainfall events responsible for the triggering of shallow landslides and debris flows and the definition of empirical rainfall thresholds. The study area is the province of Trento (6,208 km2), located in the north-eastern Alps, and characterized by complex orography, with 70% of the area at an altitude above 1,000 m. 260 debris flows and shallow landslides with known date of occurrence in the study area have been extracted from the Italian Landslide Inventory (Progetto IFFI) and descriptive statistical analysis related to the main landslide controlling factors have been performed in order to assess the representativeness of the sample with known date of activation respect to the total debris flows and shallow landslides of Trento province. An objective and rigorous statistical methodology has been defined for the identification of the beginning of the triggering event based on the critical duration, that is the minimum dry period duration separating two stochastically independent rainy periods. The critical duration has been calculated for each rain gauge of the study area and its variability during the months of the year has been analysed. An analysis of the rainfall spatial variability in a neighbourhood of the landslide detachment zone has been then carried out through the examination of the Monte Macaion radar maps during some summer convective events, the comparison of rainfall records of rain gauges located in a 10 km buffer around the landslide, and the calculation of the Pearson's correlation coefficient between pairs of neighbouring rain gauges. An automatic procedure for the identification and characterization of the triggering rainfall event has been developed, which provides in output the event duration, cumulated rainfall and average intensity, the maximum rainfall height for fixed durations (from 5 minutes to 96 hours), the cumulated antecedent rainfall (from 1 to 30 antecedent days), the maximum return period of the event, the duration, rainfall amount and intensity associated with the maximum return period. The following rainfall thresholds have been then calibrated with the frequentist approach: cumulated event rainfall-duration (E-D) and average intensity-duration (I-D), which represent the rainfall event in its entirety, and rainfall amount-duration and intensity-duration associated with the event maximum return period (ETR-DTR and ITR-DTR), which consider the most critical portion of the event therefore responsible for the landslide triggering. In the absence of information about the landslide time of activation, the end of the triggering event has been identified using two criteria: the rainfall peak intensity and the last registration of the day. The relationship between rainfall thresholds and some environmental landslide controlling factors (i.e. lithology, land use and elevation) has been analysed and finally the contribution of antecedent rainfall has been evaluated. The main outcomes of the research are: the good applicability of the methodology adopted for the objective identification of the beginning of the triggering event, the low representativeness during convective summer events of the rainfall information recorded at the nearest rain gauge with respect to the precipitation over the landslide source area, the influence of the two criteria for the identification of the end of the event on the thresholds coefficients

Metodologie di analisi e definizione di soglie di eventi pluviometrici che hanno innescato colate rapide e frane superficiali in un'area dell'arco alpino nord-orientale

Debris flows and shallow landslides, due to the high velocity, in recent decades have caused the most damage in Italy both in terms of casualties that economic losses. The triggering is in almost all cases related to intense rainfall events. For these types of landslides one of the main risk mitigation measures is the adoption of early warning systems based on rainfall thresholds that identify the critical amount of precipitation for landslide initiation. The aim of this research is the development of objective, repeatable and exportable methodologies for the identification, analysis and characterization of rainfall events responsible for the triggering of shallow landslides and debris flows and the definition of empirical rainfall thresholds. The study area is the province of Trento (6,208 km2), located in the north-eastern Alps, and characterized by complex orography, with 70% of the area at an altitude above 1,000 m. 260 debris flows and shallow landslides with known date of occurrence in the study area have been extracted from the Italian Landslide Inventory (Progetto IFFI) and descriptive statistical analysis related to the main landslide controlling factors have been performed in order to assess the representativeness of the sample with known date of activation respect to the total debris flows and shallow landslides of Trento province. An objective and rigorous statistical methodology has been defined for the identification of the beginning of the triggering event based on the critical duration, that is the minimum dry period duration separating two stochastically independent rainy periods. The critical duration has been calculated for each rain gauge of the study area and its variability during the months of the year has been analysed. An analysis of the rainfall spatial variability in a neighbourhood of the landslide detachment zone has been then carried out through the examination of the Monte Macaion radar maps during some summer convective events, the comparison of rainfall records of rain gauges located in a 10 km buffer around the landslide, and the calculation of the Pearson's correlation coefficient between pairs of neighbouring rain gauges. An automatic procedure for the identification and characterization of the triggering rainfall event has been developed, which provides in output the event duration, cumulated rainfall and average intensity, the maximum rainfall height for fixed durations (from 5 minutes to 96 hours), the cumulated antecedent rainfall (from 1 to 30 antecedent days), the maximum return period of the event, the duration, rainfall amount and intensity associated with the maximum return period. The following rainfall thresholds have been then calibrated with the frequentist approach: cumulated event rainfall-duration (E-D) and average intensity-duration (I-D), which represent the rainfall event in its entirety, and rainfall amount-duration and intensity-duration associated with the event maximum return period (ETR-DTR and ITR-DTR), which consider the most critical portion of the event therefore responsible for the landslide triggering. In the absence of information about the landslide time of activation, the end of the triggering event has been identified using two criteria: the rainfall peak intensity and the last registration of the day. The relationship between rainfall thresholds and some environmental landslide controlling factors (i.e. lithology, land use and elevation) has been analysed and finally the contribution of antecedent rainfall has been evaluated. The main outcomes of the research are: the good applicability of the methodology adopted for the objective identification of the beginning of the triggering event, the low representativeness during convective summer events of the rainfall information recorded at the nearest rain gauge with respect to the precipitation over the landslide source area, the influence of the two criteria for the identification of the end of the event on the thresholds coefficients

Probabilistic landslide ensemble prediction systems: lessons to be learned from hydrology

Landslide forecasting and early warning has a long tradition in landslide research and is primarily carried out based on empirical and statistical approaches, e.g., landslide-triggering rainfall thresholds. In the last decade, flood forecasting started the operational mode of so-called ensemble prediction systems following the success of the use of ensembles for weather forecasting. These probabilistic approaches acknowledge the presence of unavoidable variability and uncertainty when larger areas are considered and explicitly introduce them into the model results. Now that highly detailed numerical weather predictions and high-performance computing are becoming more common, physically based landslide forecasting for larger areas is becoming feasible, and the landslide research community could benefit from the experiences that have been reported from flood forecasting using ensemble predictions. This paper reviews and summarizes concepts of ensemble prediction in hydrology and discusses how these could facilitate improved landslide forecasting. In addition, a prototype landslide forecasting system utilizing the physically based TRIGRS (Transient Rainfall Infiltration and Grid-Based Regional Slope-Stability) model is presented to highlight how such forecasting systems could be implemented. The paper concludes with a discussion of challenges related to parameter variability and uncertainty, calibration and validation, and computational concerns.</p

Assessment of landslide susceptibility in Structurally Complex Formations by integration of different A-DInSAR techniques

Instability events are recurring phenomena in Southern Italy due to its geological history and tectonic-geomorphological evolution leading to the occurrence of several formations identified as Structurally Complex Formations (SCFs; Esu, 1977) in a territory mainly composed of densely populated areas also in mountainous and hilly regions. SCFs are clay-dominant terrains that, usually, give origin from very-slow to extremely-slow phenomena (Cruden and Varnes, 1996) with a long evolutionary history made up of multiple reactivations that makes difficult their identification, monitoring and susceptibility evaluation. The study has been carried out from point-wise (Bisaccia, Costa della Gaveta and Nerano cases) to wide areas (Palermo province case) where crops out SCFs as the Termini sandstones Formation (CARG, 2011), the Varicoloured Clays of Calaggio Formation (Ciaranfi et al., 1973), the Varicoloured Clays Unit (Mattioni et al., 2006) the Sicilide Unit (Vitale and Ciarcia, 2013 and references therein), the Numidian Flysch (Johansson et al., 1998) and the Corleone Calcarenites (Catalano R. et al., 2002). The aim of this thesis is to produce updated Landslide Inventory Maps and, whenever possible, Landslide Susceptibility Maps following a new approach during the landslide mapping and landslide monitoring stages. The Landslide Inventory Maps have taken into account the combination of geological, geomorphological, and stereoscopic surveys, as well as engineering geological investigations, namely conventional techniques. In addition innovative Advanced-Differential Interferometry Synthetic Aperture Radar (A-DInSAR) techniques have been used: the Coherent Pixels Technique – CPT (Mora et al., 2003; Blanco et al., 2008), the Intermittent Small BAseline Subset – ISBAS (Sowter et al., 2013) and the Ground-Based Synthetic Aperture Radar. Finally, the Weight of Evidence method (van Westen, 1993) has been chosen to generate the Landslide Susceptibility Maps only for the point-wise studies. In the case of Nerano (Province of Naples), the ISBAS analysis on ENVISAT images (for the period 2003-2010) has been carried out and compared with inclinometric and rainfall data. These have revealed several reactivations of a rotational slide + earth flow (Cruden and Varnes, 1996) that involves reworked clay olistostromes and limestone olistoliths inside the Termini sandstones Formation; even in recent years the landslide, despite many engineering works, has given evidence of a continuing activity. The results highlight a very slow movement in the detachment zone (<1 mm/yr), which assumes slightly higher values in the accumulation area (5 mm/yr). The Landslide Susceptibility Map confirms the high levels in the flow track and the accumulation area. In Bisaccia (Province of Avellino), a conglomeratic slab undergoes a Deep Seated Gravitational Slope Deformation (DSGSD; Pasuto and Soldati, 2013 and references therein) due to the bedrock consolidation, made of the Varicoloured Clays of Calaggio Formation. Here the CPT processing on ENVISAT images (covering the period between 2002 and 2010), displays a vertical displacement for the town center, suffering a progressively increasing velocity from the southern (4.2 mm/yr) to the northern (15.5 mm/yr) portion of the slab that localizes four different sectors. The pattern is confirmed from the building damage map. The landslides susceptibility reaches the highest values in the adjacent valleys and at the edges of each sector. Multiple datasets have been employed for the Costa della Gaveta case-study (Province of Potenza), these encompass: ENVISAT, TerraSAR-X and COSMO-SkyMed constellations together with Ground Based Synthetic Aperture Radar (GBSAR). The A-DInSAR data have been compared with stereoscopic analysis and the available rainfall and inclinometric data. The analysis allows for the identification of 16 landslides (complexes and earth flows; Cruden and Varnes, 1996) developed in the Varicoloured Clays Unit that show, according to all the existing instruments, velocities between 1.5 and 30 mm/yr. The western side of Costa della Gaveta slope is the portion which suffers the highest landslides susceptibility levels. In the Province of Palermo (northwestern Sicily) information deriving from A-DInSAR processing, specifically the ISBAS technique, have been focused on three subareas (Piana degli Albanesi, Marineo and Ventimiglia di Sicilia) for a total extension of 182 Km2 where standard A-DInSAR algorithms showed limitations due to the widespread presence of densely vegetated areas. The radar-detected landslides have been validated through field geomorphological mapping and stereoscopic analysis proving to be highly consistent especially with slow phenomena. The outcome has allowed to confirm 152 preexisting landslides, to detect 81 new events and to change 133 previously mapped landslides, modifying their typology, boundary and/or state of activity. The study demonstrates how a better knowledge of landslide development and their cause-effect mechanisms provided by new Earth Observation techniques is useful for Landslide Inventory and Susceptibility Maps. The research project has been carried out at the University of Naples "Federico II", including nine months (September 2013 – May 2014) spent in the United Kingdom, at the British Geological Survey under the supervision of Dr. Francesca Cigna and Dr. Jordan Colm and at the University of Nottingham (Department of Civil Engineering), under the supervision of Dr. Andrew Sowter where the ISBAS technique has been recently developed

Performance analysis of landslide early warning systems at regional scale

2014 - 2015Landslide early warning systems are non-structural risk mitigation strategies aiming at dealing with intolerably high probabilities of landslide occurrence by reducing risk through the reduction of the exposed elements. The majority of landslide early warning systems deal with rainfall-induced landslides. The systems can be classified, as a function of the scale of analysis, into: “local” and “regional” systems. Several differences exists among these two different types of warning systems, such as: the actors involved in the process, the monitoring tools, the variables selected to define triggering thresholds, the way the warnings are issued and spread to the public. This work exclusively deals with regional landslide early warning systems (ReLEWSs). These systems are used to assess the probability of occurrence of landslides over appropriately-defined homogeneous alert zones of relevant extension, typically through the prediction and monitoring of meteorological variables, in order to give generalized warnings to administrators and the population. At first, a detailed review of the structure and the functioning of these systems is presented. The information has been gathered mainly from the literature, with the exception of the regional system operating in Campania region, Italy, the municipal system of Rio de Janeiro, Brazil, and the national Norwegian landslide early warning system. The functioning and the structure of the latter two systems have been analyzed in greater depth thanks to research periods spent, respectively, at the GEO-Rio foundation in Rio de Janeiro and at The Norwegian Water Resources and Energy Directorate (NVE) in Oslo. In literature, several authors provided a general description of the structure of a landslide early warning system. Starting from the analysis of these contributions, an original scheme and the main components of such systems for rainfall-induced landslides forecast is proposed. The scheme is based on a clear distinction among the following components: correlation laws, decisional algorithm and warning management. Subsequently, the functioning of the reviewed ReLEWSs has been described according to these components, with a special attention on how the performance of the various warning models was assessed. It is straightforward that a periodical assessment of the technical performance of a landslide early warning system, in terms of evaluation of the warning issued in relation to the landslides occurred, is a required task in order to continuously keep the system reliable. Nevertheless, no standard requirements exist for assessing the performance of regional warning models (ReWaMs) and, typically, this is evaluated by computing the joint frequency distribution of landslides and warnings, both considered as dichotomous variables. Herein, an original methodology to assess the performance of ReWaMs, called the “Event, Duration Matrix, Performance” (EDuMaP) method, is proposed. The performance is evaluated taking into account: the possible occurrence of multiple landslides in the warning zone; the duration of the warnings in relation to the time of occurrence of the landslides; the warning level issued in relation to the landslide spatial density in the warning zone; the relative importance system managers attribute to different types of errors. The applicability of EDuMaP method is tested considering three different ReLEWSs: the municipal early warning system operating in Rio de Janeiro (Brazil); the Norwegian landslide early warning system; the landslide early warning system for hydro-geological risk management of the Campania region, Italy. The main differences among these systems are discussed in great detail, mainly dealing with the functioning and the databases available for the three case studies. The LEWS operational in Rio de Janeiro is employed to issue a certain level of warning in four warning zones in which the municipality is divided. The warnings can be issued at any time during the day if the monitored rainfall exceeds pre-identified thresholds. The Norwegian landslide early warning system is employed to issue daily warnings adopting variable warning zones. In the LEWS of the Campania region each municipality has a reference rain gauge for which three different rainfall threshold are specified for the activation of 3 warning levels. The EDuMaP method was successfully employed to assess the performance for all these case studies, thus underlying the wide applicability of the method, which can be easily adopted to evaluate the performance of any regional landslide early warning systems for which landslides and warnings data are available. For the three case studies, sensitivity analyses are also conducted by varying some of the input parameters of the EDuMaP method. The results of these analyses indicate that the input parameters most affecting the performance of the warning models are: i) the landslide density criterion used to differentiate among the classes of landslide events; ii) the database on landslides considered in the simulations; iii) the time set xvii as the minimum time interval between landslide events; iv) the area of analysis; v) the time frame of the analysis. In conclusion, the analyses prove the applicability of the EDuMaP method in evaluating the performance of real case studies related to ReLWaMs characterized by different decisional algorithms, components and input parameters. The method can also be used as an effective tool to calibrate a warning model by back-analysing landslide and warning data in test area with the aim of defining the set of warning criteria which maximises the model performance. [edited by author]XIV n.s

Progress in Landslide Research and Technology, Volume 1 Issue 1, 2022

This open access book provides an overview of the progress in landslide research and technology and is part of a book series of the International Consortium on Landslides (ICL). The book provides a common platform for the publication of recent progress in landslide research and technology for practical applications and the benefit for the society contributing to the Kyoto Landslide Commitment 2020, which is expected to continue up to 2030 and even beyond to globally promote the understanding and reduction of landslide disaster risk, as well as to address the 2030 Agenda Sustainable Development Goals

Landslide analysis and early warning

In jüngerer Vergangenheit aufgetretene gravitative Massenbewegungen verdeutlichen die Notwendigkeit die Vorhersagemöglichkeiten von und die Frühwarnung vor gravitativen Massenbewegungen zu verbessern, um die damit verbundenen Risiken zu reduzieren und Menschenleben zu schützen. Die vorliegende Arbeit beschäftigt sich mit lokalen und regionalen Analysen der auslösenden Bedingungen gravitativer Massenbewegungen an der Schwäbischen Alb, und der Entwicklung von Frühwarnsystem Prototypen. Im lokalen Untersuchungsgebiet wurde ein extensives hydrologisches und Hangbewegungsmonitoringsystem auf einem saisonal reaktivierten Hangrutschungskörper in Lichtenstein-Unterhausen installiert. Basierend auf der Analyse von Monitoringdaten wurde der Einfluss von Niederschlag und Schneeschmelze auf die Grundwasserbedingungen und die Initiierung von Hangbewegungen untersucht. Das kombinierte Hydrologie und Stabilitätsmodell CHASM wurde verwendet, um Hangbereiche auszuweisen, für die ein Versagen wahrscheinlich ist, und die Auswirkungen einer Vielzahl von Einflussfaktoren auf die Hangstabilität zu simulieren. Auf den Ergebnissen aufbauend wurden zwei Internet-basierte Anwendungen entwickelt. Die erste Applikation stellt ein technisches Frühwarnsystem dar, in dem die Hangstabilität unter Verwendung von gemessenem Niederschlag, hydrologischen Monitoringdaten und Wettervorhersagen fortlaufend simuliert wird. Die zweite Anwendung dient der Entscheidungsunterstützung und erlaubt eine schnelle Berechnung der Hangstabilität für frei wählbare Profile. Auf der regionalen Ebene wurden verfügbare Inventare gravitativer Massenbewegungen analysiert und hinsichtlich einer Bewertung von Niederschlagsschwellenwerte anderer Studien ausgewertet. Adäquate gravitative Massenbewegungen wurden ausgewählt und deren auslösende Niederschlags- und Schneeschmelzekonditionen mit Intensität-Dauer und kumulativen Schwellenwerten verglichen. Aufbauend auf den Ergebnissen wurde ein regionales Frühwarnsystem für gravitative Massenbewegungen entwickelt und als Internet-basiertes Anwendung implementiert. Die entwickelten lokalen und regionalen Frühwarnsysteme sind Teil einer holistischen und integrativen Frühwarnkette, welche durch das ILEWS Project implementiert wurde, und können auch auf andere von gravitativen Massenbewegungen betroffene Gebiete übertragen werden.Recent landslide events demonstrate the need to improve landslide forecasting and early warning capabilities in order to reduce related risks and protect human lives. In this thesis, local and regional investigations were carried out to analyse landslide characteristics in the Swabian Alb region, and to develop prototypic landslide early warning systems. In the local study area, an extensive hydrological and slope movement monitoring system was installed on a seasonally reactivated landslide body located in Lichtenstein-Unterhausen. Monitoring data was analysed to assess the influence of rainfall and snow-melt on groundwater conditions, and the initiation of slope movements. The coupled hydrology-slope stability model CHASM was applied to detect areas most prone to slope failures, and to simulate slope stability using a variety of input data. Subsequently, CHASM was refined and two web-based applications were developed: a technical early warning system to constantly simulate slope stability integrating rainfall measurements, hydrological monitoring data and weather forecasts; and a decision-support system allowing for quick calculation of stability for freely selectable slope profiles. On the regional scale, available landslide inventory data were analysed for their use in evaluation of rainfall thresholds proposed in other studies. Adequate landslide events were selected and their triggering rainfall and snow-melting conditions were compared to intensity-duration and cumulative thresholds. Based on the results, a regional landslide early warning system was developed and implemented as a web-based application. Both, the local and the regional landslide early warning systems are part of a holistic and integrative early warning chain developed by the ILEWS project, and could easily be transferred to other landslide prone areas