Identification of precipitation zones within São Francisco River basin (Brazil) by global wavelet power spectra

Abstract

The definition of rainfall behaviour at the regional level is of great importance in planning policy for the rational use of water resources for both agricultural and urban uses. It allows the delimitation of areas of homogeneous rainfall features and shows the system dynamics in the area, so providing more comprehensive knowledge about the rainfall. Precipitation zones were identified within the São Francisco River basin, Northeast Brazil, by analysing the rainfall frequencies by means of global wavelet power spectra. Data from 200 raingauges were analysed and the results of the overall power spectra showed a high annual frequency throughout the basin; however, other frequencies are present with minor significance that represent changes in the rainfall regime. Although, the computed global wavelet power spectra presented an annual frequency, they showed peculiar patterns (denoted A and B) that could be used to characterize the region. Thus, three sub-regions with homogeneous rainfall patterns were identified as: Region A (south part of the basin) and Region B (north part of the basin), with frequency patterns A and B, respectively, and a Transition Zone in the central part that shows both frequency patterns.

Citation Santos, C.A.G. and Morais, B.S., 2013. Identification of precipitation zones within São Francisco River basin (Brazil) by global wavelet power spectra. Hydrological Sciences Journal, 58 (4), 789–796.     

WAVERYS: a CMEMS global wave reanalysis during the altimetry period

Ocean Dynamics - As part of the Copernicus Marine Service, WAVERYS is the multi-year wave reanalysis that provides global wave data with a fine grid resolution of 1/5°. This wave reanalysis...     

On the use of linear stability model to characterize the morphological behaviour of a double bar system. Application to Truc Vert beach (France)

Sandy barred beaches are often characterized by the presence of rhythmic patterns such as crescentic bars. In this article, a linear stability analysis (LSA) model is used to characterize the morphological behaviour of the double bar system of Truc Vert beach. Using a limited number of combinations of representative bathymetries, wave classes and water levels, the morphodynamic response of the system is analysed, focussing on the geometrical characteristics of 3D patterns generated with the model. These characteristics are described and then compared with available observations. The shapes and the wavelengths of the instabilities predicted by the model compare well with field observations. Thus, the use of the linear stability model, with representative hydrodynamic conditions and bathymetries of the considered site, allows a characterization of the global morphodynamic behaviour of a double-barred system.     

Absence of oxygen isotope fractionation/exchange of (hemi-) cellulose derived sugars during litter decomposition

Aiming at developing a novel tool for palaeoclimate research, we recently proposed a new method for determining the oxygen isotope composition of monosaccharides (Zech, M., Glaser, B., 2009. Compound-specific δ¹⁸O analyses of neutral sugars in soils using GC-Py-IRMS: problems, possible solutions and a first application. Rapid Communications in Mass Spectrometry 23, 3522-3532). In order to answer the question whether isotope fractionation and oxygen exchange reactions during litter decomposition affect the climatically controlled δ¹⁸O values of plant derived sugars, such as for instance xylose and arabinose from hemicelluloses, we studied the compound specific δ¹⁸O values of five different litter species having been decomposed in a field litterbag experiment for 27 months.While δ¹⁸O values of bulk organic matter yielded a systematic ¹⁸O depletion of 3.3‰ (pine) to 4.6‰ (spruce) accompanying total cellulose decomposition of 51% (beech) to 86% (ash), δ¹⁸O values of individual sugars show no significant trend with time. In addition to the observed absence of isotope fractionation during decomposition, we also rule out ¹⁸O exchange reactions affecting the δ¹⁸O signature of sugar molecules during diagenetic processes as well as during analytical procedure based on experimental findings and on theoretical biochemical mechanistic considerations. We conclude that our new method may become an analytical tool that elegantly overcomes extraction, purity and hygroscopicity problems of previous ¹⁸O cellulose methods. It furthermore has the potential to be applied to a wide range of climate archives such as tree rings, lacustrine sediments and loess palaeosol sequences.     

The impact of African aridity on the isotopic signature of Atlantic deep waters across the Middle Pleistocene Transition

A high resolution analysis of benthic foraminifera as well as of aeolian terrigenous proxies extracted from a 37 m-long marine core located off the Mauritanian margin spanning the last ~ 1.2 Ma, documents the possible link between major continental environmental changes with a shift in the isotopic signature of deep waters around 1.0–0.9 Ma, within the so-called Mid-Pleistocene Transition (MPT) time period. The increase in the oxygen isotopic composition of deep waters, as seen through the benthic foraminifera δ¹⁸O values, is consistent with the growth of larger ice sheets known to have occurred during this transition. Deep-water mass δ¹³C changes, also estimated from benthic foraminifera, show a strong depletion for the same time interval. This drastic change in δ¹³C values is concomitant with a worldwide 0.3‰ decrease observed in the major deep oceanic waters for the MPT time period. The phase relationship between aeolian terrigeneous signal increase and this δ¹³C decrease in our record, as well as in other paleorecords, supports the hypothesis of a global aridification amongst others processes to explain the deep-water masses isotopic signature changes during the MPT. In any case, the isotopic shifts imply major changes in the end-member δ¹⁸O and δ¹³C values of deep waters.     

Calibration and application of a continuum damage model on the simulation of stone masonry structures: Gondar church as a case study

The conservation and rehabilitation of monuments is a matter of important investigation, and the need for accurate structural analysis, capable of effectively predicting the structural behaviour of this type of constructions, under static and dynamic loads, is increasing. Currently there are numerous computational methods and tools, supported by different theories and strategies with different levels of complexity, computation time and cost which are available to perform such analyses. A complex analysis is not always synonym of a better result and the choice of a method over another depends mostly on the purpose of the analysis. This work aims at evaluating the capacity of a non linear continuum damage model (Faria et al. in Int J Solids Struct 35(14):1533–1558, 1998), originally developed for concrete structures, to simulate the behaviour of stone masonry structures. In particular, the seismic response of an old stone masonry construction, the Gondar church, is analysed considering different levels of geometrical and material complexity. The verification and calibration procedures use the experimental results from tests performed on stone masonry walls at the Laboratory for Earthquake and Structural Engineering of the Faculty of Engineering of Porto University and from other tests found in the bibliography (Vasconcelos in Experimental investigations on the mechanics of stone masonry: Characterization of granites and behaviour of ancient masonry shear walls. PhD Thesis, Universidade do Minho, Guimar?es, Portugal, 2005). The results are compared, assessing the differences and the importance of using complex tools, such as the continuum damage model, to better simulate and understand the global behaviour of such constructions.