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- Landslide susceptibility assessment using different rainfall event-based landslide inventories: advantages and limitationsPublication . Oliveira, Sérgio; Zêzere, José; Garcia, Ricardo; Pereira, Susana; Vaz, Teresa; Melo, RaquelThe present work aims to evaluate potential sources of uncertainty associated with rainfalltriggered event-based landslide inventories within the framework of landslide susceptibility assessment. Therefore, this study addresses the following questions: (i) How representative is an event-based landslide inventory map of the total landslide activity and distribution in a study area?; (ii) How reliable is an event-based landslide susceptibility map?; (iii) How appropriate is an event-based landslide inventory map for independently validating a landslide susceptibility map? To address these questions, two independent and contrasting rainfall event-based landslide inventories were used, together with a historical landslide inventory, to assess landslide susceptibility for diferent types of landslides in a study area located north of Lisbon, Portugal. The results revealed the following fndings: (i) contrasting rainfall critical conditions for failure can trigger similar landslide types, although they may vary in size and be spatially constrained by diferent predisposing conditions, particularly lithology and soil type; (ii) landslide susceptibility models using event-based landslide inventories are not reliable in the study area, regardless of the landslide inventory map used for training and validation; and (iii) complementary sources of uncertainty results from using incomplete historical landslide inventories to assess landslide susceptibility and non-totally independent landslide inventories for modeling validation. The present study enhances the understanding of regional landslide susceptibility patterns based on contrasting rainfall-trigger conditions, providing valuable information to minimize exposure; to design regional landslide early warning systems for specifc rainfall-trigger landslide events; and to improve the response and preparedness of civil protection services.
- Integration of landslide susceptibility maps for land use planning and civil protection emergency managementPublication . Oliveira, Sérgio; Zêzere, José; Guillard, Clemence; Garcia, Ricardo A C; Pereira, SusanaLandslides are one of the most relevant geomorphological hazards in Portugal, by the high levels of people affected, destruction of assets and disruption of economic and social activities. Regarding the Portuguese territorial land use planning and emergency management, regulation, practice, prevention and risk management have been promoted in different ways. In Portugal, the areas susceptible to landslides are included in the 'National Ecological Reserve', which is a public utility restriction legal figure that rules the land use planning at the municipal level. In addition, the Municipal Emergency Plans include landslide susceptibility maps that are combined with the map of the exposed elements, allowing the assessment of exposure to landslides. This study is applied to the Loures municipality located to the north of Lisbon. In this municipality 621 landslides registered in a landslide inventory (rotational slides, deep-seated translational slides and shallow translational slides) that affected 1,469,577 m2 (0.87 %) of the Loures territory. The final landslide susceptibility map shows that in Loures municipality 1,347 ha are associated to a Very high landslide susceptibility and 2,372 ha to High landslide susceptibility, which corresponds both to 22.1 % of the entire municipality, and constitutes the larger fraction of the National Ecological Reserve, related to landslides. These areas do not present geomorphological and geotechnical suitability for building structures or infrastructures. From the civil protection and emergency management point of views 34 classes of exposed elements were identified in the municipality, with point, linear and polygonal representations. The elements at risk located in the Very High or High landslide susceptibility classes were summarized and correspond to: high voltage poles; wind turbines; transmission/reception antennas; industrial areas; water tanks; silo; gas station/tank; service area; buildings of educational institutions; worship buildings; buildings of electricity facilities; regular buildings; gas pipeline; motorways; national roads; and municipal roads.
- Padrão de deformação de movimentos de vertente em áreas periurbanasPublication . Oliveira, Sérgio; Zêzere, José; Garcia, Ricardo A C; Pereira, SusanaThe occurrence of landslides triggered by intense or long-lasting rainfall events in the region north of Lisbon has produced considerable material losses related with the partial or full destruction of infrastructures, in particularly roads and buildings. This problem becomes more relevant in the peri-urban areas as it is the case of the Grande da Pipa River basin that registered a potential growth resulting from the proximity of the Lisbon city. As an exploratory approach, this study allowed to evaluate the damage pattern in buildings and roads as consequence of landslides occurrence. To achieve that goal the following topics were considered: the resistance of the exposed element, the intensity of the landslide, and the spatial relationship between the exposed element and the different sectors of the landslide that affect it. For buildings the lack of data did not allow to define any deformation pattern. In the case of roads three different deformation patterns can be inferred by the way roads relate with the landslide sector which originates the damage. When the landslide rupture surface is located above the road the damage level registered was negligible. When the road is located within the landslide area the degree of loss registered increased (slight loss or significant). When the road is affected by a landslide scarp or landslide flank, variable degrees of loss were observed which appear to be dependent on the vertical steps existing in the landslide scarp or flanks.
- On the Physical Vulnerability of Buildings Exposed to Landslide Hazards in the Lisbon Metropolitan AreaPublication . Cardoso, Ana; Pereira, Susana; Ferreira, Tiago Miguel; Zêzere, José; Melo, Raquel; Vaz, Teresa; Oliveira, Sérgio; Garcia, Ricardo; Santos, Pedro Pinto; Reis, EusébioThis study assesses the physical vulnerability of buildings (PVB) in the Lisbon Metropolitan Area (LMA) exposed to landslides triggered by both rainfall and earthquakes. Firstly, a statistical model (Information Value), validated with a ROC curve, was adopted to assess susceptibility to landslides caused by rainfall. Secondly, an Analytic Hierarchy Process was adopted to assess the susceptibility to landslides caused by earthquakes. In this case, the model was validated with an inventory of historical landslides in the LMA. The vulnerability assessment included all residential buildings surveyed in the 2011 Census, considering a set of vulnerability parameters, namely: the presence of reinforced structure, number of floors, conservation status, and need for repairs in the structure and finishes. These parameters, and their respective weights, were based on expert opinion and literature. Through this analysis, it was possible to identify meaningful regional interactions between the earthquake and rainfall-triggered landslides, leading to complex damage scenarios for residential buildings. It was also possible to identify risk hotspots and potential risk adaptation and mitigation measures.
- Assessment of buildings exposure and potential losses to landslides based on census dataPublication . Oliveira, Sérgio; Melo, Raquel; Alves, Carlos; Rocha, Jorge; Garcia, Ricardo; Tavares, Alexandre; Zêzere, José; Pereira, Susana; Santos, Pedro Pinto; Morgado, Paulo; Marques Da Costa, NunoLandslides, like any natural hazardous process, do not generate risk until some type of interaction with human settlements or activities occur. Consequently, the landslide susceptibility assessment and the quantification of the exposure and potential losses of structures and infrastructures is crucial for informing emergency and spatial planning in areas prone to geomorphological hazards. Thus, the major aim of this work is to identify the current and future buildings’ exposure to landslides, in order to get useful information to support decision planners. The current spatial distribution of buildings and future exposure trends will be assessed based on the Portuguese Census data, which will be used as ancillary information to derive the number and type of buildings at the basic census polygonal unit. The future buildings’ exposure will be determined from a cellular automata simulation model. Four types of buildings are considered: E1 – light structures of wood or metal; E2 – buildings of adobe, rammed earth or loose stone walls; E3 - buildings with brick or stone masonry walls; and E4 - buildings of masonry walls confined with reinforced concrete. The evaluation of buildings’ exposure is made for two landslide event scenarios: one for shallow soil slips (with rupture surfaces depth < 1.5 m) and another one for deep-seated slides (with rupture surfaces depth > 1.5 m). The landslide susceptibility/hazard hotspots for both scenarios are assessed in a study area corresponding to four municipalities located in the northern sector of the Lisbon Metropolitan Area, Portugal. The landslide susceptibility models are based on a bivariate statistical method (Information Value) and on a dataset of eight independent variables assumed as predisposing factors for the occurrence of landslides: lithology, slope, curvature, aspect, slope/contribution area ratio, topographic position index (TPI), soil type and land use. The validation procedures include the computation of ROC curves and the calculation of AUROC. Landslide susceptibility and buildings’ exposure are presented as probabilities at the basic census unit scale. Results combine the probability of occurrence of a landslide with the probability of having a building of a certain type potentially affected by a landslide, for the two landslide event scenarios. Finally, potential losses on buildings are assessed from exposure and damage on buildings caused by landslides in the past.