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- Rainfall thresholds for landslide activity in Portugal: a state of the artPublication . Zêzere, José; Vaz, Teresa; da Silva Pereira, Susana; Oliveira, Sérgio; Marques, R.; Garcia, Ricardo A CRainfall is the most important physical process responsible for the landslide triggering in Portugal. Results obtained worldwide have shown that control of rainfall on landslides differs substantially depending upon landslide depth and kinematics and the affected material. Therefore, the critical rainfall conditions for failure are not the same for different types of landslides, and may be strongly influenced by regional geologic and geomorphologic conditions. Rapid debris flows are typically triggered by very intense showers concentrated in just a few hours, and shallow translational soil slips are usually triggered by intense precipitation falling within the 1–15 days long range. On the contrary, activity of deep-seated landslides of rotational, translational and complex types is related to periods of nearly constant rainfall, lasting from several weeks to several months. The different rainfall intensity–duration conditions are associated with different hydrologic mechanisms for slope failure. The generation of surface run-off and high peak discharges in first-order mountain catchments is a critical triggering mechanism for debris flows. The intense rainfall allows the rapid growth of pore water pressure and the drop of capillarity forces that sustain the apparent cohesion of thin soils. As a consequence, shallow soil slips occur within the soil material or at the contact with the underlying less permeable bedrock. Long lasting rainfall episodes enable the steady rise of the groundwater table and the development of positive pore water pressures into the soil. Consequently, deep-seated failures occur in relation to the reduction of shear strength of affected materials. In this work, we present the state of the art concerning the proposition of empirical rainfall thresholds in Portugal for different types of landslides observed in different zones of the country: the Lisbon region, the Douro Valley and the NW Mountains, and the Povoação Municipality in São Miguel Island (Azores). The empirical thresholds applied in Portugal are based on the identification of past landslide events and include (i) the computation of antecedent rainfall threshold defined by linear regression, (ii) the normalization of rainfall by the mean annual precipitation, (iii) the definition of lower limit and upper limit rainfall thresholds and (iv) the definition of combined rainfall thresholds, which integrates the rainfall event and the antecedent rainfall for different time periods.
- Uncertainty into statistical landslide susceptibility models resulting from terrain mapping units and landslide input dataPublication . Zêzere, José Luís; Pereira, Susana; Melo, Raquel; Oliveira, Sérgio; Garcia, Ricardo A C
- Perfis municipais de risco a cheias e inundações para aplicação ao ordenamento do território em Portugal continentalPublication . Pereira, Susana; Santos, Pedro Pinto; Zêzere, José; Reis, Eusébio; Santos, Mónica; Garcia, Ricardo A C; Oliveira, Sérgio; Rocha, Jorge; Fragoso, Marcelo; Vaz, Teresa; Meneses, Bruno; Rilo, Ana; Bateira, Carlos
- Assessing population exposure for landslide risk analysis using dasymetric cartographyPublication . Garcia, Ricardo A C; Oliveira, Sérgio; Zêzere, JoséAssessing the number and locations of exposed people is a crucial step in landslide risk management and emergency planning. The available population statistical data frequently have insufficient detail for an accurate assessment of potentially exposed people to hazardous events, mainly when they occur at the local scale, such as with landslides. The present study aims to apply dasymetric cartography to improving population spatial resolution and to assess the potentially exposed population. An additional objective is to compare the results with those obtained with a more common approach that uses, as spatial units, basic census units, which are the best spatial data disaggregation and detailed information available for regional studies in Portugal. Considering the Portuguese census data and a layer of residential building footprint, which was used as ancillary information, the number of exposed inhabitants differs significantly according to the approach used. When the census unit approach is used, considering the three highest landslide susceptible classes, the number of exposed inhabitants is in general overestimated. Despite the associated uncertainties of a general cost–benefit analysis, the presented methodology seems to be a reliable approach for gaining a first approximation of a more detailed estimation of exposed people. The approach based on dasymetric cartography allows the spatial resolution of population over large areas to be increased and enables the use of detailed landslide susceptibility maps, which are valuable for improving the exposed population assessment.
- Weather and climate versus mortality in Lisbon (Portugal) since the 19th centuryPublication . Alcoforado, Maria Joao; Marques, David; Garcia, Ricardo A C; Canário, Paulo; Nunes, Maria de Fátima; Nogueira, Helena; Cravosa, AnaA renewed interest on the impacts of climate change has spurred several studies on climate/health relationships. This study aims to detect and explain any changes in the relationships between climate and mortality in Lisbon from 1835 until 2012. The evaluation of mortality seasonal rhythms over time is based on the 100-Index per decades, annual Winter-Summer ratio, as well as other descriptive statistics. A change in the seasonal rhythm of mortality over the last 177 years was found. In the mid-19th century mortality peaked in summer, whereas in the 1890s and the 1900s there was slight monthly variability. On the contrary, a winter maximum has occurred since the 1940s, although a secondary summer peak of mortality may emerge during the most severe heat-waves. Although long term positive temperature trends were confirmed, no systematic positive mortality trends were found in the last three decades. The results suggest that mortality rhythm changes during the 19th and 20th century are not directly related to climatic reasons alone (except in the case of extreme weather events), but rather to improvements in hygienic, sanitary and nutrition conditions and advances in medicine. However, given the possible increase of summer heat waves in the future, and individuals increasing vulnerability, particularly in urban areas, such secondary peaks of mortality will tend to happen more frequently, unless adaptation of populations to hotter conditions takes place and/or measures are taken to protect people from high temperatures.
- Modelação em sistemas de informação geográfica da avaliação da susceptibilidade a movimentos de vertente na área amostra de Lousa-Loures (Região a norte de Lisboa)Publication . Piedade, Aldina; Zêzere, José; Tenedório, José António; Garcia, Ricardo; Oliveira, Sérgio; Rocha, JorgeA avaliação da susceptibilidade a movimentos de vertente baseia-se no princípio de que os factores que condicionaram a actividade de deslizamentos no passado e presente serão igualmente responsáveis pela ocorrência dos futuros episódios de instabilidade geomorfológica. A metodologia utilizada neste trabalho teve por base duas questões de partida: i) sendo conhecida a variação espacial da susceptibilidade de uma área é viável a aplicação directa dos scores de susceptibilidade correspondentes em áreas que apresentem características geológicas e geomorfológicas similares? ii) qual é o grau de erro introduzido por esta abordagem em comparação com a avaliação de susceptibilidade mais habitual, baseada na exploração do inventário de movimentos de vertente da área teste? A aplicação e validação de um modelo de susceptibilidade na área de Lousa-Loures (área teste) com recurso a algoritmos obtidos para a área de Fanhões-Trancão (área modelo), justificase pelo facto destas áreas terem características geológicas e geomorfológicas similares e pela existência da mesma tipologia de deslizamentos, nomeadamente os deslizamentos translacionais superficiais. Paralelamente, é desenvolvida a avaliação da susceptibilidade na área de Lousa- Loures, com recurso ao inventário de deslizamentos translacionais superficiais dessa área. Foram criadas e utilizadas bases de dados relacionais que transcrevem as relações entre os factores de predisposição da instabilidade e os deslizamentos translacionais superficiais, com recurso à modelação através de Sistemas de Informação Geográfica (SIG). Para possibilitar as comparações, procedeu-se à homogeneização dos dados de partida nas duas áreas e utilizou-se uma única ferramenta estatística para avaliar a susceptibilidade: o Método do Valor Informativo. Os resultados obtidos são validados através de técnicas estandardizadas, descritas na literatura especializada (e.g. Chung e Fabbri, 2003; Guzzetti, 2005) e já aplicados em estudos similares na região a norte de Lisboa (e.g. Reis et al., 2003; Zêzere et al., 2004).
- Perfis municipais de risco de instabilidade de vertentesPublication . Pereira, Susana; Santos, Pedro Pinto; Zêzere, José; Tavares, Alexandre Oliveira; Reis, Eusébio; Garcia, Ricardo A C; Oliveira, Sérgio
- Distribuição da densidade de probabilidade da magnitude de deslizamentos na região norte de Lisboa, PortugalPublication . Garcia, Ricardo; Oliveira, Sérgio; Zêzere, JoséEste trabalho tem como principal objectivo a análise da distribuição da densidade de probabilidade e o estabelecimento de uma curva de probabilidade-magnitude para os deslizamentos ocorridos na região norte de Lisboa (RNL). Assumindo que a área é um indicador fiável da magnitude de um movimento de vertente, a sua distribuição de densidade de probabilidade pode ser a base para o cálculo da probabilidade de ocorrência de um movimento de vertente com uma determinada dimensão. O seu ajuste à função gamma inversa de três parâmetros pode ser efectuado a diferentes bases de dados cujos critérios de partição foram a profundidade do plano de ruptura ou a unidade litológica. Os resultados revelam que as distribuições de densidade de probabilidade apresentam em termos gerais uma forma similar à distribuição geral descrita na literatura. No entanto, serão necessárias, algumas, modificações da parametrização para melhor se ajustar à realidade da RNL. Curvas de magnitude obtidas com bases de dados parciais apresentam diferenças significativas quando comparadas com a obtida com o inventário total, que sobrestima e subestima algumas probabilidades de ocorrência. As curvas de magnitude definidas especificamente para cada unidade litológica parecem ser uma opção para minimizar este problema.
- 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.
- Integration of landslide susceptibility maps for land use planning and civil protection emergency managementPublication . Oliveira, Sérgio C.; Zêzere, José; Guillard-Gonçalves, Clémence; 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 1347 ha are associated to a Very high landslide susceptibility and 2372 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 presente 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; servisse area; buildings of educational institutions; worship buildings; buildings of electricity facilities; regular buildings; gas pipeline; motorways; national roads; and municipal roads.