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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.
- A comparison between bivariate and multivariate methods to assess susceptibility to liquefaction-related coseismic surface effects in the Po Plain (Northern Italy)Publication . Lanfredi Sofia, C.; Oliveira, Sérgio; Pereira, Susana; Zêzere, José; Corsini, A.The two main events occurred during the 2012 seismic sequence on the Po Plain in Northern Italy (May 20 Mw 5.9 and May 29 Mw 5.8) induced widespread coseismic surface effects (CSEs), mostly liquefaction phenomena, which caused severe damages. To prevent risks related to CSE, an important non-structural measure is to assess locations susceptible to liquefaction, which is usually done at site scale by means of deterministic approaches in micro-zonation studies. This paper brings a novel methodological contribution in the field of CSE susceptibility mapping at regional scale, by testing and comparing bivariate (Weights of Evidence) and multivariate (Logistic Regression) methods that, so far, have not yet been used for such purpose. In a study area of 1480 km2 , the computation used an inventory of CSE as supporting evidence and a set of maps with geologic, geomorphic, hydrogeological and topographic factors as causal variables. Both methods provided susceptibility maps with a significant predictive capability and a fairly good spatial agreement between each other. In conclusion, this application of data-driven spatial modelling approaches indicates that such methods can be effectively used for liquefaction susceptibility zonation at regional scale, which can be of significant support for spatial planning over large areas.
- 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
- On the Multi-hazard Risk Assessment of Urban Areas: Identification and Analysis of Exposure and Physical Vulnerability IndicatorsPublication . Xofi, Maria; Domingues, José Carlos; Santos, Pedro Pinto; Pereira, Susana; Oliveira, Sérgio; Reis, Eusébio; Zêzere, José; Garcia, Ricardo; Lourenço, Paulo B.; Ferreira, Tiago MiguelThe development of integrated decision-support tools, able to assess multiple hazards at the regional and local scales, is a fundamental step to enhance the preparedness of urban areas to mitigate present and future risks arising from climate change. Understanding multi-hazard risk can help prioritize resilience-increasing actions and disaster prevention measures and form the basis for exploring institutional adjustments that improve stakeholders’ capacities to manage risk. Within this framework, the present research work aims to identify and analyze a set of exposure and buildings’ vulnerability indicators to be used as input to a multi-hazard risk assessment methodology. Exposure is to be measured using a dimensionless score resulting from the quantitative identification of the elements at risk. Regarding the physical vulnerability of buildings, it is to be evaluated on a hazard-by-hazard basis using a large-scale parametric-based vulnerability assessment approach. Finally, the obtained exposure and physical vulnerability indicators are to be put together in order to create different data layers, which are then used to identify hotspot risk areas. The Metropolitan Area of Lisbon, Portugal, is used as a pilot study area to discuss the applicability and potential of the proposed indicators.
- Evento hidrogeomorfológico de fevereiro de 1979: condições atmosféricas e impactosPublication . Rebelo, Luís; Ramos, Alexandre M.; Pereira, Susana; Trigo, RicardoThe large amount of floods and landslides that occurred on 5-16 February 1979 in Portugal corresponds to a major hydro-geomorphologic event according to the comprehensive DISASTER database. This event is driven by atmospheric forcing at different time scales that have not been, as yet, studied in detail. Here we show that the precipitation period of February 1979 has produced several multiday accumulated precipitation events, over the Portuguese continental territory, ranking amongst the top 10 events observed between 1950 and 2008. Additionally, most of the precipitation on this event occurs in days with atmospheric circulation dominated by “wet” circulation weather types (CWTs), i.e. cyclonic (C), west (W) or southwest (SW) types.
- 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
- Cartografia de 150 anos de ocorrências hidrogeomorfológicas catastróficas: Portugal continental um território de inquietaçãoPublication . Tavares, Alexandre Oliveira; Barros, José Leandro; Santos, Pedro Pinto; Pereira, SusanaA partir da recolha hemerográfica, em jornais de circulação nacional e regional, no período entre 1865 e 2015 em Portugal continental, foi construída uma base de dados - DISASTER - com os locais geograficamente identificáveis, afetados por cheias, inundações ou por movimentos de massa em vertentes, aos quais se associam perdas humanas (mortos, feridos, desaparecidos ou desalojados), independentemente do seu número. Os resultados mostram a evolução decenal das ocorrências, a distribuição por bacia hidrográfica e por unidades morfo-estruturais. Transparece uma distribuição global de ocorrências por todo o território continental português, com concentração de ocorrências e de impactos humanos em margens dos rios Douro e seus afluentes, no Médio e Baixo Tejo, no Baixo Mondego e Águeda, os quais são marcados dominantemente por processos de cheias progressivas ou rápidas. Verifica-se igualmente a concentração de pontos em espaços com uso e ocupação urbana intensa, como são Lisboa e o Porto e os seus municípios adjacentes, assim como a região de Coimbra ou o Algarve, em que as cheias e os processos de instabilidade de vertentes originam impactos humanos. Os episódios hidro-geomorfológicos constituem, assim, processos naturais a que se associam perdas humanas com mortos e feridos, ou um elevado número de evacuados e desalojados, traduzindo um território de inquietação para a população e para os gestores do risco.
- A evolução temporal dos tipos de inundações com danos humanos no concelho de Lisboa (1865-2010)Publication . Leal, Miguel; Ramos, Catarina; Pereira, Susana
- Desastres hidrogeomorfológicos na Região Centro de Portugal Continental entre 1990 e 2015Publication . Tavares, Alexandre Oliveira; Barros, José Leandro; Santos, Pedro Pinto; Pereira, Susanapara os desastres de origem hidro-geomorfológica. Este facto tem sido relacionado com o aumento da frequência e magnitude das cheias e movimentos de massa em vertentes, consequência das alterações climáticas e de um incorreto uso e ocupação do solo que origina um aumento da exposição de pessoas e bens face ao risco. A construção de Base de Dados de desastres revestese de uma enorme importância, pois permite analisar e compreender a incidência temporal e espacial dos processos e impactos decorrentes. Em Portugal Continental destaca-se a base de dados DISASTER para desastres hidro-geomorfológicos ocorridos no período de 1865-2010. Esta base de dados possibilitou a recolha e sistematização de informação sobre cheias, inundações e movimentos de vertente, permitindo o aumento do conhecimento científico sobre os mesmos [...]