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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
- Journalistic approach of hydro-geomorphological events in the beginning of the industrial pressPublication . Antunes, M .N.; Pereira, Susana; Zêzere, José Luís; Oliveira, A. E.In contemporary societies the media is oriented to cover disaster considering the intersection between three dimensions of risk: hazard, exposure and vulnerability. In the past, the prevailing theory was the naturalization of disasters that considered disasters as extreme events generated by the nature, where human action did not influence disaster occurrences and consequences. In view of the predominant theory of the nature of disasters, the objective of this work is to analyze the approach of journalism on disasters in the early 20th century. This research explores a catalogue of hydro-geomorphological events selected from the Disaster database for the period 1865–1909, which were reported by the Portuguese newspaper Diário de Notícias (DN). News analysis was guided by the News Protocol. The news set highlighted the naturalization of disasters, the focus on post-disaster consequences and local correspondents as the main source reporting disaster occurrences in the territory.
- Hydro-geomorphologic events in Portugal and its association with Circulation weather typesPublication . Pereira, Susana; Ramos, Alexandre M.; Rebelo, Luís; Trigo, Ricardo M.; Zêzere, José
- Disaster journalism in print media: analysis of the top 10 hydrogeomorphological disaster events in Portugal, 1865–2015Publication . Antunes, Michele Nacif; Pereira, Susana; Zêzere, José; Oliveira, Adauto EmmerichDisaster communication guidelines emphasize that journalists should be aware of past major disasters and draw lessons from the coverage of those events. The press is an important source for the evolution of historical disaster and risk research paradigms over time. This study explored the top 10 damaging hydrogeomorphological events in Portugal selected from the disaster database, which includes events that caused human damages (fatalities, injured, missing, evacuated, and displaced) reported over a period of 151 years (1865–2015) by the Portuguese newspaper Diário de Notícias (DN). News analysis was guided by the news protocol. The analysis of the news published in DN enabled us to identify textual marks that present interconnections in the journalistic coverage and produce discursive standards for these disasters. The textual marks were associated with the hazard and risk paradigms. The discursive standards of DN did not clearly reflect the ruptures in the hazard paradigms. As a rule, the journalistic reports contributed to the naturalization of disasters and the gap in public understanding of risks, by presenting an approach focused on relief actions—ignoring social issues, vulnerability, and population resilience—reducing the discourse of preparedness for future disasters.
- Flood susceptibility assessment based on Analytical Hierarchy Process: application in mainland PortugalPublication . Santos, Pedro Pinto; Pereira, Susana; Zêzere, José; Reis, Eusébio; Garcia, Ricardo A C; Oliveira, Sérgio; Santos, MónicaAlthough the scientific and computational advances in the hydrological study of flood hazard assessment, a demand still exists concerning more expedite and extensive methods to map flood susceptibility or proneness over large areas. The relevant question is very often to achieve the best equilibrium between the complexity of flood hazard models and the accuracy and quantity of the input data. The presented study aims to assess flood susceptibility in mainland Portugal through the application of an Analytical Hierarchy Process (AHP), using 17 flood susceptibility conditioning factors related with: i) terrain morphology (elevation, slope angle, slope over area ratio, flow accumulation, topographic position index, landform classification - Jenness); ii) basin morphology (hypsometric integral, Gravelius index, circularity ratio and the orographic coefficient of Fournier); iii) permeability (lithology, , alluvial zones, hydraulic conductivity and ecological zones); iv) rainfall (water balance) and v) hydrography (drainage density and Strahler’s fluvial hierarchy). All variables were classified according to empirical knowledge and further defined as raster datasets at the national level with a resolution of 25x25 m cell size. AHP technique was used to achieve the relative weights based on the Saaty’s scale of influence, which ranges between 1 and 9. The weighting of conditioning factors was performed at two levels: initially, between variables and, secondly, between the different classes of each variable. This later process, although consensual regarding most of the variables (e.g., slope angle or flow accumulation) is rather more complex regarding specific variables which require a deeper interpretation of scores (e.g., topographic position index, landform classification and the permeability-related variables). The study also highlights the challenges posed during the data preparation and integration steps, namely, the integration of data from variables that are represented at the basin level (e.g., those related to basin morphometry and hydrologic behavior) with data represented on a cell-by-cell basis, such as flow accumulation or slope angle. Future exploration of the results includes the aggregation of the AHP-based flood susceptibility scores – distinguishing progressive floods from flash floods – at the administrative level, achieving a flood susceptibility municipal index in order to verify to each extend disastrous floods have been controlled by natural constrains at the municipal level. Such indexes will be applied later in decision support systems in order to define public civil protection-related resources.
- DISASTER: a GIS database on hydro-geomorphologic disasters in PortugalPublication . Zêzere, José; Pereira, Susana; Tavares, A. O.; Bateira, C.; Trigo, R. M.; Quaresma, I.; Santos, P. P.; Santos, M.; Verde, J.In the last century, Portugal was affected by several natural disasters of hydro-geomorphologic origin that often caused high levels of destruction. However, data on past events related to floods and landslides were scattered. The Disaster project aims to bridge the gap on the availability of a consistent and validated hydro-geomorphologic database for Portugal, by creating, disseminating and exploiting a GIS database on disastrous floods and landslides for the period 1865–2010, which is available in http://riskam.ul.pt/disaster/en. Data collection is steered by the concept of disaster used within the Disaster project. Therefore, any hydro-geomorphologic case is stored in the database if the occurrence led to casualties or injuries, and missing, evacuated or homeless people, independently of the number of people affected. The sources of information are 16 national, regional and local newspapers that implied the analysis of 145,344 individual newspapers. The hydro-geomorphologic occurrences were stored in a database containing two major parts: the characteristics of the hydro-geomorphologic case and the corresponding damages. In this work, the main results of the Disaster database are presented. A total of 1,621 disastrous floods and 281 disastrous landslides were recorded and registered in the database. These occurrences were responsible for 1,251 dead people. The obtained results do not support the existence of any exponential increase in events in time, thus contrasting with the picture provided to Portugal by the Emergency Events Database. Floods were more frequent during the period 1936–1967 and occurred mostly from November to February. Landslides were more frequent in the period 1947–1969 and occurred mostly from December to March.
- Análise de clusters municipais de cheias/inundações e movimentos de massa em vertentes danosos em PortugalPublication . Pereira, Susana; Rocha, Jorge; Zêzere, José
- Avaliação da suscetibilidade das linhas de água a cheias utilizando análise multicritérioPublication . Santos, Pedro Pinto; Pereira, Susana; Reis, Eusébio; Santos, Mónica
- Mortality patterns of hydro-geomorphologic disastersPublication . da Silva Pereira, Susana; Zêzere, José; Quaresma, I.; Santos, P. P.; Santos, M.Social impacts caused by floods and landslides in Portugal in the period of 1865-2010 are gathered in the DISASTER database. This database contains 1,902 hydro-geomorphologic cases that caused 1,248 fatalities (81% and 19% associated with floods and landslides, respectively). The use of the DISASTER database allowed for: (i) the analysis of the frequency and the temporal evolution of fatal floods and landslides; (ii) the analysis of the spatio-temporal distribution of fatalities; (iii) the identification of the most deadly flood and landside types; (iv) the verification of gender tendencies in mortalities; and (v) the evaluation of individual and societal risk. The highest number of flood and landslide cases and related mortalities occurred in the period of 1935-1969. After this period, the number of flood and landslide mortalities decreased, although landslide fatalities remained higher than those registered in the period of 1865-1934. The occurrence of flood fatalities was widespread in the country, with an important cluster in the Lisbon region and in the Tagus valley, while fatalities caused by landslides mainly occurred in the north of the Tagus valley. Flash floods caused the majority of fatalities associated with floods, while falls and flows were responsible for the highest number of fatalities associated with landslides. Males were found to have the highest frequency of fatalities. In the case of floods, the majority of fatalities were found both outdoors and inside of buildings in rural areas while fatalities inside buildings were dominant in landslide cases, mostly in rural areas.
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