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- A landslide risk index for municipal land use planning in PortugalPublication . Pereira, Susana; dos Santos, Pedro; Zêzere, José; Tavares, A. O.; Garcia, R.A.C.; Oliveira, S.In Portugal landslides caused 237 fatalities and >1600 displaced people in the period 1865-2015. Spatial distribution and temporal patterns of slope instability can be related with a complex set of natural and human factors responsible for generating damages. It is essential to develop new methodologies to synthetize risk dimensions to contribute to the landslide risk management at the municipal level. This work proposed a municipal landslide risk index (LRI) considering three risk dimensions: hazard, exposure and physical vulnerability of buildings. The hazard dimension includes the landslide susceptibility performed at the national scale, the probability of weather types associated with landslides and an extreme precipitation susceptibility index. The exposure dimension considered the population density and the number of buildings, whereas the average physical vulnerability of the buildings was computed using four statistical variables from the official census: (i) construction technique and construction materials; (ii) reinforced structure; (iii) number of floors; and (iv) conservation status. Each variable includes different classes that were empirically weighted. After evaluating the three risk dimensions and the LRI, a cluster analysis was performed in order to identify the most important landslide risk drivers in each municipality. Exposure is the main driving force of LRI in the metropolitan areas of Lisbon and Porto, while the hazard is more relevant in the NW municipalities and the physical vulnerability is the major driving force in the south of the country. This methodological approach contributes to a comprehensive and synthetized knowledge about the landslide risk driving forces within the 278 Portuguese municipalities. In addition, it contributes to the diversification and context-oriented strategies of landslide risk management that still lacks in most of the national-level risk governance processes. Finally, this methodology can be generalized to other geographical contexts, improving the risk management, land use planning and the disaster risk reduction.
- Assessing sea level rise exposure and social vulnerability scenarios for sustainable land use planningPublication . Trindade, Jorge; Zêzere, José; Reis, Eusébio; Rocha, Jorge; Santos, Pedro Pinto; Garcia, Ricardo; Oliveira, Sérgio; Pereira, SusanaThe climate change scenarios, with sea level rise and increased frequency of extreme hydro- meteorological events, associated with the growing pressure on the coastal zone, highlight the need to improve the ability to predict risk factors under future scenarios and assess impacts in these territories at global and national level. Starting from the current scenario, the High Waters research project intends to contribute to the definition of a roadmap of adaptation and mitigation measures for coastal risks in the medium and long term. Taking 2040, 2070 and 2100 as time stamps it aims at analysing the future hazard, exposure and vulnerability over Portuguese coastal areas. The project aims also to elaborate municipal risk profiles to support proposals of management strategies for coastal zones, using various methods, including fieldwork, statistical and remote sensing data processing and application of machine learning techniques.
- A comprehensive approach to understanding flood risk drivers at the municipal levelPublication . Santos, Pedro Pinto; Pereira, Susana; Zêzere, José; Tavares, Alexandre Oliveira; Reis, Eusébio; Garcia, Ricardo A C; Oliveira, SérgioDuring the period 1998–2017, floods were responsible for 11% of the loss of life and 23% of the economic loss caused by climate-related and geophysical-related disasters worldwide. An integrated and effective definition of flood risk management strategies therefore still requires synthesized and comprehensive knowledge about the driving forces of flood risk. In this study, 278 Portuguese municipalities are analyzed and classified according to flood hazard, exposure, and vulnerability. After evaluating the three components that describe risk, an index of the flood risk is calculated and a cluster analysis is further performed to understand the role of the risk drivers (hazard, exposure, and vulnerability) in each municipality. The proposed approach therefore provides flood risk indexes on a municipal basis, which are built upon different sources of both cell-by-cell data and an aggregation of municipal-level data that has been statistically validated. Municipalities both in the NW part of the country and along the valleys of major rivers demonstrate a significant superimposition of high levels of exposure and hazard, while vulnerability presents a disperse pattern throughout the country. The results obtained using this approach should contribute to the diversification of flood risk management strategies. This is still lacking in the majority of the national-level flood risk governance processes, namely those strategies that focus on the contingency of daily activities and those aiming at a long-term reduction of the exposure, vulnerability, and hazard components that shape flood disasters.
- Landslide quantitative risk analysis of buildings at the municipal scale based on a rainfall triggering scenarioPublication . da Silva Pereira, Susana; Garcia, Ricardo A C; Zêzere, José; Oliveira, Sérgio; Silva, MárcioA landslide quantitative risk analysis is applied the municipality of Santa Marta de Penagui~ao (N of Portugal) to evaluate the risk to which the buildings are exposed, using a vector data model in GIS. Two landslide subgroups were considered: landslide subgroup 1 (event inventory of landslides occurred on January 200)1; and landslide subgroup 2 (inventoried landslides occurred after the 2001 event until 2010). Seven landslide predisposing factors were weighted and integrated using the Information Value Method. The landslide susceptibility model was independently validated and the model performance was expressed by ROC curves. The probability of landslide size was estimated using a probability density function and the landslide hazard scenario was defined using the same landslide rainfall-triggering event. A vulnerability curve was constructed for each type of building considering its structural properties and the proxy of landslide magnitude. The economic value assigned for each building represents an approximated cadastral value. The landslide risk was computed for each building in vector format based on a rainfall triggering scenario and two landslide magnitudes. The probability of occurrence of small landslides is two orders of magnitude higher than the probability of occurrence for large landslides, which explains the higher risk generated by small landslides, despite of registering.
- 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.
- Probabilistic landslide risk analysis considering direct costs in the area north of Lisbon (Portugal)Publication . Zêzere, José; Garcia, R.A.C.; Oliveira, Sérgio; Reis, EusébioThe purpose of the present study is the analysis of landslide risk for roads and buildings in a small test site (20 km2) in the area north of Lisbon (Portugal). For this purpose, an evaluation is performed integrating into a GIS information obtained from multiple sources: (i) landslide hazard; (ii) elements at risk; and (iii) vulnerability. Landslide hazard is assessed on a probabilistic basis for three different types of slope movement (shallow translational slides, translational slides and rotational slides), based on some assumptions such as: (i) the likelihood of future landslide occurrence can be measured through statistical relationships between past landslide distribution and specified spatial data sets considered as landslide predisposing factors; and (ii) the rainfall combination (amount–duration) responsible for past slope instability within the test site will produce the same effects (i.e. same type of landslides and similar total affected area), each time they occur in the future. When the return period of rainfall triggering events is known, different scenarios can be modelled, each one ascribed to a specific return period. Therefore, landslide hazard is quantitatively assessed on a raster basis, and is expressed as the probability for each pixel (25 m2) to be affected by a future landslide, considering a rainfall triggering scenario with a specific return period. Elements at risk within the test site include 2561 buildings and roads amounting to 169 km. Values attributed to elements at risk were defined considering reconstruction costs, following the guidelines of the Portuguese Insurance Institute. Vulnerability is considered as the degree of loss to a given element resulting from the occurrence of a landslide of a given magnitude. Vulnerability depends not only on structural properties of exposed elements, but also on the type of process, and its magnitude; i.e., vulnerability cannot be defined in absolute terms, but only with respect to a specific process (e.g. vulnerability to shallow translational slides). Therefore, vulnerability was classified for the three landslide groups considered on hazard assessment, taking into account: (i) landslide magnitude (mean depth, volume, velocity); (ii) damage levels produced by past landslide events in the study area; and (iii) literature. Finally, a landslide risk analysis considering direct costs was made in an automatic way crossing the following three layers: (i) Probabilistic hazard map for a landslide type Z, considering a particular rainfall triggering scenario whose return period is known; (ii) Vulnerability map (values from 0 to 1) of the exposed elements to landslide type Z; and (iii) Value map of the exposed elements, considering reconstruction costs.