Spatial and temporal patterns of dry spell lengths in the Iberian Peninsula for the second half of the twentieth century

Summary Daily pluviometric records of 43 meteorological stations across the Iberian Peninsula have permitted a detailed analysis of dry spell patterns for the period 1951–2000 by distinguishing daily amount thresholds of 0.1, 1.0, 5.0 and 10.0 mm/day. The analyses are based on three annual series, namely the number of dry spells, N, the average dry spell length, L, and the extreme dry spell length, L _max. First, the statistical significance of local trends for the annual series of N, L and L _max has been investigated by means of the Mann-Kendall test and significant field trends have been established by means of Monte Carlo simulations. Clear signs of negative field trends are detected for N (1.0 and 10.0 mm/day) and L (0.1 mm/day). Second, the Weibull model fits well the empirical distributions of dry spell lengths for all the rain gauges, whatever the daily amount threshold, with a well ranged spatial distribution of their parameters u and k. On the basis of the Weibull distribution, return period maps for 2, 5, 10, 25 and 50 years have been obtained for dry spell lengths with respect to the four daily threshold levels. While for 0.1 and 1.0 mm/day the longest dry spells are expected at the south of the Iberian Peninsula, for 5.0 and 10.0 mm/day they are mostly detected at the southeast. Finally, the elapsed time between consecutive dry spells has been analysed by considering the same rain amount thresholds and different dry spell lengths at increasing intervals of 10 days. This analysis makes evident a significant negative field trend of the elapsed time between consecutive dry spells of lengths ranging from 10 to 20 days for daily amount thresholds of 1.0, 5.0 and 10.0 mm/day. Authors’ addresses: X. Lana, C. Serra, Departament de Física i Enginyeria Nuclear, ETSEIB, Universitat Politècnica de Catalunya, Av. Diagonal 647 planta 11, 08028 Barcelona, Spain; M. D. Marínez, Departament de Física Aplicada, Universitat Politècnica de Catalunya, 08028 Barcelona, Spain; A. Burgue?o, Departament de Meteorologia i Astronomia, Universitat de Barcelona, 08028 Barcelona, Spain; J. Martín-Vide, L. Gómez, Grup de Climatologia, Universitat de Barcelona, 08028 Barcelona, Spain.     

A New Appraisal of Sri Lankan BB Zircon as a Reference Material for LA‐ICP‐MS U‐Pb Geochronology and Lu‐Hf Isotope Tracing

A potential zircon reference material (BB zircon) for laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) U‐Pb geochronology and Hf isotope geochemistry is described. A batch of twenty zircon megacrysts (0.5–1.5 cm³) from Sri Lanka was studied. Within‐grain rare earth element (REE) compositions are largely homogeneous, albeit with some variation seen between fractured and homogeneous domains. Excluding fractured cathodoluminescence bright domains, the variation in U content for all analysed crystals ranged from 227 to 368 μg g^?1 and the average Th/U ratios were between 0.20 and 0.47. The Hf isotope composition (0.56–0.84 g/100 g Hf) is homogeneous within and between the grains – mean ¹⁷⁶Hf/¹⁷⁷Hf of 0.281674 ± 0.000018 (2s). The calculated alpha dose of 0.59 × 10¹⁸ g^?1 for a number of BB grains falls within the trend of previously studied, untreated zircon samples from Sri Lanka. Aliquots of the same crystal (analysed by ID‐TIMS in four different laboratories) gave consistent U‐Pb ages with excellent measurement reproducibility (0.1–0.4% RSD). Interlaboratory assessment (by LA‐ICP‐MS) from individual crystals returned results that are within uncertainty equivalent to the TIMS ages. Finally, we report on within‐ and between‐grain homogeneity of the oxygen isotope systematic of four BB crystals (13.16‰ VSMOW).     

Electrical Imaging of Impact Structures

Electrical imaging provides important subsurface information for the construction of hypervelocity impact models. We here provide an overview and evaluation of the current electrical imaging methods used in impact cratering studies. Although apparent resistivity models are commonly used in the geoelectrical imaging of impact structures, the reliability of these models has not hitherto been determined. In order to assess these imaging approaches in impact cratering, we investigate for the first time the discrepancies between the apparent resistivity and true resistivity models of an impact structure. To this end, we present (1) a new true resistivity model of the Araguainha impact structure in central Brazil by applying L2-norm inversion to previously published data, (2) apparent resistivity model of the impact structure, and (3) models obtained from different stages of the iterative tomographic inversions. Our results show that changes in vertical resistivity gradient are significantly better defined in the true resistivity models than in the apparent resistivity model. On the basis of these results, we outline a new approach that true resistivity models can be effectively assessed by applying both L1- and L2-norm inversion schemes together with the monitoring of intermediate models from iterative inversion. The results of our study highlight the importance of tomographic inversion of resistivity data in impact cratering studies, and they provide a data modeling framework and foundation for cost-effective subsurface imaging of impact structures in the future.     

Hydrological response of an afforested catchment in a Mediterranean humid mountain area: a comparative study with a natural forest

The effects of afforestation on water resources are still controversial. The aim of this paper is to (i) analyse the hydrological response of an afforested area in the Central Pyrenees and (ii) compare the hydrological response of an afforested area with the response observed in a natural undisturbed forest. The Araguás catchment was cultivated until the 1950s, and then afforested with pines in an effort to control the active degradation processes. The hydrological response was variable and complex, because the discharge was generated by a combination of distinct runoff processes. The hydrological response showed that (i) afforestation produced moderate peak discharges, stormflows and recession limbs, and long rising limbs; (ii) no one single variable was able to explain the hydrological response: rainfall volume and intensity did not explain the hydrological response and antecedent rainfall and initial discharge (indicating antecedent moisture conditions) did play an important role; (iii) seasonal differences were observed suggesting different runoff generating processes; and (iv) the effect of forest cover on peak discharges became less important as the size of the hydrological event increased. The stormflow coefficient showed a clear seasonal pattern with an alternation between a wet period, when the catchment was hydrologically responsive, and a dry summer period when the catchment rarely responded to any event, and two transitional periods (wetting and drying). Compared with a natural forest, the afforested area recorded greater flows and peak discharges, faster response times and shorter recession limbs. Afforestation reduces the water yield and the number of floods compared with non‐vegetated areas and abandoned lands. Copyright © 2016 John Wiley & Sons, Ltd.     

Morphosedimentary analysis of the Limoeiro Stream (center-northern Minas Gerais State,Brazil): clues to the eastward tilting of southern Espinhaco range sites

The morphosedimentary evolution of a sector of the southern Espinhaco range (northern Minas Gerais State, Brazil) and its regional neotectonic setting are presented herein. The studied site is a stream at base level flowing along the western border of the range. Its identification was accomplished by using remote sensing techniques including the analysis of 3D slope models generated with shuttle radar topography mission images. The main geomorphological features of the identified site were surveyed in a 1:500 scale. In addition, seven stratigraphic logs are described. A regional geologic compilation and facies diagrams were used as a basis for the integration of the geomorphological and stratigraphic data, which produced some conclusions about the recent tectonic reactivations at the eastern border of Sao Francisco Craton. The results point to a local eastward tilting of the Espinhaco range. This fact is in accordance with previous findings in neighboring areas and results in the asymmetric evolution of the fluvial valley, as well as the regional relief.     

Is the cutting of oil contaminated marshes an efficient clean-up technique in a subtropical estuary?

Cutting and removal of oil-impacted marsh plants are still used worldwide as a clean-up and recovery technique. To experimentally test the efficacy of cutting and removing marsh plants under subtropical conditions, we simulated an oil spill (Bunker MF-180) in Spartina alterniflora marshes and compared the responses of plant height, biomass, density of culms and number of flowering plants in high and low energy areas in Paranaguá Bay (S Brazil) for about 9 months. Cutting and removal were inefficient in promoting or accelerating the recovery of the impacted areas. Cut or uncut impacted marshes fully recovered within 6 months, both in low and high energy areas. Plant cutting should be practiced only when there is an effective risk of contamination of groundwater near urban areas, when obvious aesthetical issues are involved in areas of touristic interest or when there are real short-term conservation risks to threatened species.     

Surface Synoptic Circulation and Daily Precipitation in Catalonia

Summary Catalonian daily precipitation patterns were obtained by means of S-mode Principal Component Analysis (PCA) applied to subsets built up according to synoptic surface airflow. Daily data from November to April 1990–1994 from 45 raingauge sites in Catalonia without missing data were used. Eight circulation classes for days in this period were considered. A Precipitation Activity Index (PAI) was calculated for each station and class, leading to the determination of the highest activity regions for each subset. In addition, we determined which circulation type produced most precipitation at each station of the network. Separate PCAs were performed for each of the eight classes considered and the first four Varimax rotated solutions were interpreted for each circulation type. The physical meaning of the rest of the factors were omitted as they were associated with local behaviour. Finally, some concluding remarks on the cyclogenic properties of the Western Mediterranean Basin and the diversity of the extracted patterns are presented and supported by the authors experience in forecasting in Catalonia. Received February, 11, 1997 Revised May 23, 1997     

S?o Francisco-Congo Craton break-up delimited by U-Pb-Hf isotopes and trace-elements of zircon from metasediments of the Ara?uaí Belt

Detrital zircon U-Pb geochronology combined with Hf isotopic and trace element data from metasedimentary rocks of the Aracuai Belt in southeastern Brazil provide evidence for break-up of the Congo-Sao Francisco Craton. The U-Pb age spectra of detrital zircons from metasediments of the Rio Doce Group(RDG) range from 900-650 Ma and define a maximum depositional age of ca. 650 Ma. Zircon trace element and whole rock data constrain an oceanic island arc as source for the deposition setting of the protoliths to the metasediments. Zircon ε_(Hf)(t) values from these rocks are positive between +1 and +15, supporting previous evidence of a Neoproterozoic extensional phase and oceanic crust formation in a precursor basin to the Aracuai Belt. Recrystallization of detrital zircon at ca. 630 Ma is compatible with a regional metamorphic event associated with terrane accretion to the Paleoproterozoic basement after transition from an extensional to a convergent regime. The juvenile nature, age spectra and trace element composition recorded in detrital zircons of metasediments from the Aracuai Belt correspond with zircons from metasedimentary rocks and oceanic crust remnants of other orogenic belts to its south. This suggests that rifting and oceanic crust formation of the entire orogenic system, the so-called Mantiqueira Province, was contemporaneous, most likely related to the opening of a large ocean. It further indicates that the cratonic blocks involved in the orogenic evolution of the Mantiqueira Province were spatially connected as early as 900 Ma.     

Rainfall intensity patterns derived from the urban network of Barcelona (NE Spain)

Theoretical and Applied Climatology - An analysis of the normalised rainfall intensity curves in Barcelona (NE Spain) has been undertaken from 41 selected rain rate episodes recorded by an urban...