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

A first step towards a IoT-based local early warning system for an unsaturated slope in Norway

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Assessing potential building damage caused by leakage to urban tunnels

Building damage is a major risk for urban tunnelling. In areas with soft soil conditions, water ingress to bedrock tunnels can cause significant pore pressure reduction, consolidation settle-ments and damage to nearby buildings and infrastructure. In Norway, guidelines to determine leakage limits are based on a national database, containing data on water ingress, pore pressure reduction and influence zone. To support future projects, the database has been implemented into an ArcGIS-tool and merged with the Ground Impact and Building Vulnerability (GIBV) method to assess potential building damage at early project stages. This paper presents the adopted methodology and shows its application for a new subway tunnel in Oslo, Norway.Assessing potential building damage caused by leakage to urban tunnelsacceptedVersio

Landslide risk reduction through close partnership between research, industry, and public entities in Norway: Pilots and case studies

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A monitored unsaturated slope in Norway: Eidsvoll case study

In steep unsaturated slopes, the unsaturated region has a crucial role in maintaining the slope stability. In this work, the hydrological behaviour of a natural unsaturated slope located adjacent to a railway track in Eastern Norway has been modelled. Due to its steep inclination, the slope is monitored, and its stability is kept under frequent observation. The commercial software GeoStudio was used to create and calibrate a model able to replicate the in-situ monitored soil water content conditions. Six simulations were carried out by changing the initial and boundary climate conditions of the slope. The simulations conducted were divided into two main series: one with an initial calibration of the VWC profile (C), and another with no calibration (NC). For each of them, three different surface boundary conditions were applied: i) only precipitation, ii) precipitation and atmospheric conditions, iii) precipitation, atmospheric conditions and vegetation, according to the Penman-Monteith equation for evapotranspiration. The simulations have been validated though the use of Taylor diagrams that graphically summarize how closely a pattern (or a set of patterns) matches observations. The results show that including an initial calibration, climate conditions and vegetation, is crucial to best model the response of an unsaturated slope in Norway. The effectiveness of the best simulation in back-calculating soil water content, was tested for 3 different time periods: 3-month, 6-month, 1-year. The results show that the hydrological model can adequately represent the real monitored conditions up to a 6-month period, afterward a recalibration is needed. In addition, a coupled seepage and slope stability analysis for the 6-month period has been carried out. The calculated FS varies up to 18% depending on the complexity of the boundary conditions used in the model. The findings of this work can be seen as a preliminary step towards a real-time slope stability analysis and local landslide early warning system (Lo-LEWS).publishedVersio

Preface: Landslide early warning systems: monitoring systems, rainfall thresholds, warning models, performance evaluation and risk perception

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Leveranse 5.2. Delprosjekt 5 – Risiko

Hensikten med verktøyet er å systematisk identifisere og vurdere risiko for uønskede hendelser. Risikomatrisen som genereres kan danne grunnlag for valg av anleggsmetoder og behov for avbøtende tiltak. Risikovurderingen vil også være mulig å oppdatere i ulike prosjektfaser og vil være nyttig ved kommunikasjon av risiko blant prosjektets ulike aktører