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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.
- 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.
- Effects of landslide inventories uncertainty on landslide susceptibility modellingPublication . Zêzere, José; Neves, Mário; Henriques, C. S.; Garcia, Ricardo; Oliveira, Sérgio; Piedade, Aldina
- Flood susceptibility assessment through statistical models and HEC-RAS analysis for sustainable management in Essaouira Province, MoroccoPublication . Khouz, Abdellah; Trindade, Jorge; Santos, Pedro Pinto; Oliveira, Sérgio; El Bchari, Fatima; Bougadir, Blaid; Garcia, Ricardo; Reis, Eusébio; Jadoud, Mourad; Saouabe, Tarik; Rachidi, SaidFloods are natural disasters that often impact communities living in low-lying areas in the northern and central parts of Morocco. In this study, our aim was to create a flood susceptibility map using three methods; the hierarchy process (AHP) frequency ratio model (FR) and the weights of evidence (WoE) model. We extensively examined the area identified by these approaches using a hydraulic analysis software called HEC-RAS (version 6.3.1). Our analysis focused on the Essaouira watersheds in Morocco, where we identified around 197 flood locations. Out of these, we randomly selected 70% for modeling purposes while the remaining 30% were used for validation. Ten factors that influence floods were considered, such as slope, elevation, proximity to rivers, drainage density, stream order, land use patterns, rainfall data, lithology (permeability level) index (TWI), and curvature. We obtained these factors from data sources. Finally, we generated a flood susceptibility map and evaluated its accuracy by calculating the area under the curve (AUC). The validation results confirmed that all three models were robust and effective with an AUC of 90. Moreover, the research uncovered a trend of vulnerability with the most susceptible area being in close proximity to the city of Essaouira along the Oued Ksob. A detailed analysis using HEC-RAS was conducted at this identified location, pinpointing the village of Diabat as highly exposed. These findings hold significance for flood management, empowering decision makers, scholars, and urban planners to make informed choices and implement strategies that can minimize the impact of floods in susceptible regions while minimizing potential damages.
- 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.
- 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.
- Spatial correlates of COVID-19 first wave across continental PortugalPublication . Barbosa, Bruno; Silva, Melissa; Capinha, César; Garcia, Ricardo; Rocha, JorgeThe first case of COVID-19 in continental Portugal was documented on the 2nd of March 2020 and about seven months later more than 75 thousand infections had been reported. Although several factors correlate significantly with the spatial incidence of COVID-19 worldwide, the drivers of spatial incidence of this virus remain poorly known and need further exploration. In this study, we analyse the spatiotemporal patterns of COVID-19 incidence in the at the municipality level and test for significant relationships between these patterns and environmental, socioeconomic, demographic and human mobility factors to identify the mains drivers of COVID-19 incidence across time and space. We used a generalized liner mixed model, which accounts for zero inflated cases and spatial autocorrelation to identify significant relationships between the spatiotemporal incidence and the considered set of driving factors. Some of these relationships were particularly consistent across time, including the ‘percentage of employment in services’; ‘average time of commuting using individual transportation’; ‘percentage of employment in the agricultural sector’; and ‘average family size’. Comparing the preventive measures in Portugal (e.g., restrictions on mobility and crowd around) with the model results clearly show that COVID-19 incidence fluctuates as those measures are imposed or relieved. This shows that our model can be a useful tool to help decision-makers in defining prevention and/or mitigation policies.
- 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.