3,862 research outputs found
The hydro-geomorphologic event of february 1979: weather conditions and impacts
The 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.info:eu-repo/semantics/publishedVersio
Revisiting the outstanding flooding episode of November 1967 in the greater metropolitan Lisbon area
The deadliest storm affecting Portugal since, at least, the early 19th century, took place on the 25 and 26 November 1967 causing more than 500 fatalities. Here we provide a comprehensive multi-disciplinary assessment of this episode, including the main socio-economic impacts, particularly the numbers and location of victims (dead, injured, homeless and evacuated). Based on the sub-daily time series of a representative station, and its Intensity-Duration-Frequency curves, we have found that the exceptionality of this rainfall event is particularly linked to rainfall intensities ranging in duration from 4 to 9 hours compatible with return periods of 100-years or more. This range of time scale is similar to the estimated concentration time values of the hydrographic basins affected by the flash flood event. Most victims were sleeping or were caught by surprise at home in the small river catchments within the greater metropolitan Lisbon area. The majority of people who died or who were severely affected by the flood lived in degraded housing conditions often raised in a clandestine way, occupying flood plains near the stream beds. This level of destruction observed at the time is in stark contrast to what was observed in subsequent episodes of similar amplitude. In particular, since 1967 the Lisbon area, was struck by two comparable intense precipitation events in 1983 and 2008 but generating considerably fewer deaths and evacuated people.info:eu-repo/semantics/publishedVersio
Eventos hidrogeomorfológicos em Portugal e a sua associação com os "weather types"
In recent years it has been possible to improve the characterization of past floods and landslides that caused human and economic impact in Portugal for the 1865-2015 period. In this regard there is an urge for a more systematic assessment of the atmospheric circulation at the synoptic scale associated to flood and landslide damaging events to correctly characterize the climatic forcing of hydro-geomorphologic risk in Portugal. Here we provide a comprehensive analysis of the atmospheric circulation based on the weather type classification, an automated version of the Lamb weather type procedure, initially developed for the United Kingdom and often named circulation weather types (CWT) and latter adapted for Portugal.info:eu-repo/semantics/publishedVersio
{\it Ab initio} NMR chemical shifts and quadrupolar parameters for phases and their precursors
The Gauge-Including Projector Augmented Wave (GIPAW) method, within the
Density Functional Theory (DFT) Generalized Gradient Approximation (GGA)
framework, is applied to compute solid state NMR parameters for in
the , , and aluminium oxide phases and their gibbsite
and boehmite precursors. The results for well-established crystalline phases
compare very well with available experimental data and provide confidence in
the accuracy of the method. For -alumina, four structural models
proposed in the literature are discussed in terms of their ability to reproduce
the experimental spectra also reported in the literature. Among the considered
models, the structure proposed by Paglia {\it et al.} [Phys. Rev.
B {\bf 71}, 224115 (2005)] shows the best agreement. We attempt to link the
theoretical NMR parameters to the local geometry. Chemical shifts depend on
coordination number but no further correlation is found with geometrical
parameters. Instead our calculations reveal that, within a given coordination
number, a linear correlation exists between chemical shifts and Born effective
charges
Validation of 3-day rainfall forecast at the regional scale
Nearly half of the natural disasters in the world are due to hydro-geomorphological hazards. Therefore, rainfall forecast is a key parameter for the implementation of landslides and flash-floods early warning systems. In this work we developed a routine in R software that enables the validation of a 3-day rainfall forecast by comparison with the daily rainfall data recorded in 101 automatic meteorological stations available in mainland Portugal. The routine integrates the pre-processing of base data, the matching between the 3-day rainfall forecast and the daily rainfall registered in the automatic meteorological stations based on sequence of days, the estimation of the difference between the forecasted and the real rainfall values and the computation of error measures, such as the bias, the mean absolute error, the mean absolute percentage error and the root mean square error. The results from the error measures, estimated for the 101 automatic meteorological stations, are then exported to an excel file. The routine is implemented for mainland Portugal and tested using data from February 2015, however, the spatial and temporal data can be easily updated for other regions
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