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61.
Present and future climatologies in the phase I CREMA experiment 总被引:1,自引:0,他引:1
Erika Coppola Filippo Giorgi Francesca Raffaele Ramon Fuentes-Franco Graziano Giuliani Marta LLopart-Pereira Ashu Mamgain Laura Mariotti Gulilat Tefera Diro Csaba Torma 《Climatic change》2014,125(1):23-38
We provide an overall assessment of the surface air temperature and precipitation present day (1976–2005) and future (2070–2099) ensemble climatologies in the Phase I CREMA experiment. This consists of simulations performed with different configurations (physics schemes) of the ICTP regional model RegCM4 over five CORDEX domains (Africa, Mediterranean, Central America, South America, South Asia), driven by different combinations of three global climate models (GCMs) and two greenhouse gas (GHG) representative concentration pathways (RCP8.5 and RCP4.5). The biases (1976–2005) in the driving and nested model ensembles compared to observations show a high degree of spatial variability and, when comparing GCMs and RegCM4, similar magnitudes and more similarity for precipitation than for temperature. The large scale patterns of change (2070–2099 minus 1976–2005) are broadly consistent across the GCM and RegCM4 ensembles and with previous analyses of GCM projections, indicating that the GCMs selected in the CREMA experiment are representative of the more general behavior of current GCMs. The RegCM4, however, shows a lower climate sensitivity (reduced warming) than the driving GCMs, especially when using the CLM land surface scheme. While the broad patterns of precipitation change are consistent across the GCM and RegCM4 ensembles, greater differences are found at sub-regional scales over the various domains, evidently tied to the representation of local processes. This paper serves to provide a reference view of the behavior of the CREMA ensemble, while more detailed and process-based analysis of individual domains is left to companion papers of this special issue. 相似文献
62.
Lluís Casas Boutheina Fouzai Marta Prevosti Nejia Laridhi‐Ouazaa Ramon Jrrega Siwar Baklouti 《Geoarchaeology》2016,31(6):564-576
Two isolated kilns of unknown age and three well‐dated artifacts from Tunisia have been investigated using archaeomagnetic techniques. Dating has been attempted for the kilns and archaeomagnetic intensities have been obtained for the artifacts. The kilns lack datable artifacts although one of them (Sidi Zahruni) could be related to a nearby late Roman site. Comparison with the SCHA.DIF.3K regional geomagnetic model suggests for both kilns two possible periods of last use, either Roman or Medieval. Three archaeomagnetic intensities were obtained for the well‐dated ceramic artifacts adding to scarce archaeomagnetic data from Africa. The new data along with recently published archaeointensities from other Tunisian sites have been compared with the regional model SCHA.DIF.3K, its updated version, and the global ARCH3k.1 geomagnetic model. The models show relatively good agreement with the new archaeointensities and with previously published intensities. The uncertainty of the experimental data tends to increase for older artifacts, and their agreement with the geomagnetic models diminishes. The observed trend of the intensity models to underestimate values in the Tunisian area for the Roman period could be overcome by adding new data from well‐dated artifacts from North African, particularly from pre‐Roman and Roman sites. 相似文献
63.
Jose Ramon B. Cantalice Moacyr Cunha Filho Borko D. Stosic Victor Casimiro Piscoya Sergio M. S. Guerra Vijay P. Singh 《水文科学杂志》2013,58(8):1789-1802
AbstractSuspended sediment and bedload discharges in sand-bed rivers shape semi-arid landscapes and impact sediment delivery from these landscapes, but are still incompletely understood. Suspended sediment and bedload fluxes of the intermittent Exu River, Brazil, were sampled by direct measurements. The highest suspended sediment concentration observed was 4847.4 mg L-1 and this value was possibly associated with the entrainment of sediment that was deposited in the preceding year. The bedload flux was well related to the stream power and the river efficiently transported all available bedload with a mean rate of 0.0047 kg m-1 s-1, and the percentage of bedload to suspended sediment varied between 4 and 12.72. The bed sediment of Exu River was prone to entrainment and showed a proclivity for transport. Thus, sand-bed and gravel-bed rivers of arid environments seem to exhibit the same mobility in the absence of armour layer.Editor D. Koutsoyiannis; Associate editor B. TouaibiaCitation Cantalice, J.R.B., Cunha Filho, M., Stosic, B.D., Piscoya, V.C., Guerra, S.M.S., and Singh, V.P., 2013. Relationship between bedload and suspended sediment in the sand-bed Exu River, in the semi-arid region of Brazil. Hydrological Sciences Journal, 58 (8), 1789–1802. 相似文献
64.
Telm Bover‐Arnal Ramon Salas Joan Guimerà Josep Anton Moreno‐Bedmar 《Sedimentology》2014,61(6):1558-1593
Long‐term relative sea‐level cycles (0·5 to 6 Myr) have yet to be fully understood for the Cretaceous. During the Aptian, in the northern Maestrat Basin (Eastern Iberian Peninsula), fault‐controlled subsidence created depositional space, but eustasy governed changes in depositional trends. Relative sea‐level history was reconstructed by sequence stratigraphic analysis. Two forced regressive stages of relative sea‐level were recognized within three depositional sequences. The first stage is late Early Aptian age (intra Dufrenoyia furcata Zone) and is characterized by foreshore to upper shoreface sedimentary wedges, which occur detached from a highstand carbonate platform, and were deposited above basin marls. The amplitude of relative sea‐level drop was in the order of tens of metres, with a duration of <1 Myr. The second stage of relative sea‐level fall occurred within the Late Aptian and is recorded by an incised valley that, when restored to its pre‐contractional attitude, was >2 km wide and cut ≥115 m down into the underlying Aptian succession. With the subsequent transgression, the incision was backfilled with peritidal to shallow subtidal deposits. The changes in depositional trends, lithofacies evolution and geometric relation of the stratigraphic units characterized are similar to those observed in coeval rocks within the Maestrat Basin, as well as in other correlative basins elsewhere. The pace and magnitude of the two relative sea‐level drops identified fall within the glacio‐eustatic domain. In the Maestrat Basin, terrestrial palynological studies provide evidence that the late Early and Late Aptian climate was cooler than the earliest part of the Early Aptian and the Albian Stage, which were characterized by warmer environmental conditions. The outcrops documented here are significant because they preserve the results of Aptian long‐term sea‐level trends that are often only recognizable on larger scales (i.e. seismic), such as for the Arabian Plate. 相似文献
65.
Paulo Lojkasek‐Lima Ramon Aravena Orfan Shouakar‐Stash Shaun K. Frape Massimo Marchesi Stephanie Fiorenza John Vogan 《Ground Water Monitoring & Remediation》2012,32(4):53-62
A pilot‐scale zero valent iron (ZVI) Permeable Reactive Barrier (PRB) was installed using an azimuth‐controlled ‐vertical hydrofracturing at an industrial facility to treat a chlorinated Volatile Organic Compound (VOC) plume. Following ZVI injection, no significant reduction in concentration was observed to occur with the exception of some multilevel monitoring wells, which also showed high levels of total organic carbon (TOC). These patterns suggested that the zero valent iron was not well distributed in the PRB creating leaky conditions. The geochemical data indicated reducing conditions in these areas where VOC reduction was observed, suggesting that biotic processes, associated to the guar used in the injection of the iron, could be a major mechanism of VOC degradation. Compound‐Specific Isotope Analysis (CSIA) using both carbon and chlorine stable isotopes were used as a complementary tool for evaluating the contribution of abiotic and biotic processes to VOC trends in the vicinity of the PRB. The isotopic data showed enriched isotope values around the PRB compared to the isotope composition of the VOC source confirming that VOC degradation is occurring along the PRB. A batch experiment using site groundwater collected near the VOC source and the ZVI used in the PRB was performed to evaluate the site‐specific abiotic isotopic fractionation patterns. Field isotopic trends, typical of biodegradations were observed at the site and were different from those obtained during the batch abiotic experiment. These differences in isotopic trends combined with changes in VOC concentrations and redox parameters suggested that biotic processes are the predominant pathways involved in the degradation of VOCs in the vicinity of the PRB. 相似文献
66.
Marta Tárraga Servando De La Cruz-Reyna Ana T. Mendoza-Rosas Roberto Carniel Alicia Martínez-Bringas Alicia García Ramon Ortiz 《Acta Geophysica》2012,60(3):664-681
The continuous background seismic activity contains information on the internal state of a volcanic system. Here, we report
the influence of major regional tectonic earthquakes (M > 5 in most cases) on such state, reflected as changes in the spectral and dynamical parameters of the volcano continuous
seismic data. Although changes do not always occur, analysis of five cases of earthquake-induced variations in the signals
recorded at Popocatépetl volcano in central México reveal significant fluctuations following the tectonic earthquakes. External
visible volcanic activity, such as small to moderate explosions and ash emissions, were related to those fluctuations. We
briefly discuss possible causes of the variations. We conclude that recognition of fluctuations in the dynamical parameters
in volcano monitoring seismic signals after tectonic earthquakes, even those located in the far field, hundreds of kilometers
away, may provide an additional criterion for eruption forecasting, and for decision making in the definition of volcanic
alert levels. 相似文献
67.
Lidia Romero-Viana Ramon Julià Antonio Camacho Eduardo Vicente Maria Rosa Miracle 《Journal of Paleolimnology》2008,40(2):703-714
Lake La Cruz is a meromictic, karstic lake with annually laminated sediment formed by summer pulses of calcite deposition.
The aim of this study was to explore the potential use of the laminated sediment from Lake La Cruz as a quantitative climate
proxy, by calibrating lamina thickness against instrumental climate data. Statistical analysis of the relation between lamina
thickness and the meteorological dataset indicated a high correlation between calcium carbonate lamina thickness and rainfall
from December to March (r = 0.725, P < 0.01, n = 35). Winter rainfall anomalies in the area are, in turn, highly negatively correlated with the North Atlantic Oscillation
index (NAO, r = −0.832; P < 0.01; n = 53). We propose a regression model to infer past winter rainfall from calcium carbonate laminae thickness. These results
highlight new possibilities for paleoenvironmental research using calcite laminated sediment records as climate proxies, especially
to study past rainfall variability. 相似文献
68.
Groundwater control on the suspended sediment load in the Na Borges River, Mallorca, Spain 总被引:1,自引:0,他引:1
Groundwater dominance has important effects on the hydrological and geomorphological characteristics of river systems. Low suspended sediment concentrations and high water clarity are expected because significant inputs of sediment-free spring water dilute the suspended sediment generated by storms. However, in many Mediterranean rivers, groundwater dominance is characterised by seasonal alternations of influent and effluent discharge involving significant variability on the sediment transport regimes. Such areas are often subject to soil and water conservation practices over the centuries that have reduced the sediment contribution from agricultural fields and favour subsurface flow to rivers. Moreover, urbanisation during the twentieth century has changed the catchment hydrology and altered basic river processes due to its ‘flashy’ regime. In this context, we monitored suspended sediment fluxes during a two-year period in the Na Borges River, a lowland agricultural catchment (319 km2) on the island of Mallorca (Balearic Islands). The suspended sediment concentration (SSC) was lower when the base flow index (i.e., relative proportion of baseflow compared to stormflow, BFI) was higher. Therefore, strong seasonal contrasts explain the high SSC coefficient of variation, which is clearly related to dilution effects associated with different groundwater and surface water seasonal interactions. A lack of correlation in the Q-SSC rating curves shows that factors other than discharge control sediment transport. As a result, at the event scale, multiple regressions illustrate that groundwater and surface water interactions are involved in the sedimentary response of flood events. In the winter, the stability of baseflow driven by groundwater contributions and agricultural and urban spills causes hydraulic variables (i.e., maximum discharge) to exert the most important control on events, whereas in the summer, it is necessary to accumulate important volumes of rainfall, creating a minimum of wet conditions in the catchment to activate hydrological pathways and deliver sediment to the drainage network. The BFI is also related to sediment delivery processes, as the loads are higher with lower BFI, corroborating the fact that most sediment movement is caused by stormflow and its related factors. Overall, suspended sediment yields were very low (i.e., < 1 t km− 2 yr− 1) at all measuring sites. Such values are the consequence of the limited sediment delivery attributable to soil conservation practices, low surface runoff coefficients and specific geomorphic features of groundwater-dominated rivers, such as low drainage density, low gradient, steep valley walls and flat valley floors. 相似文献
69.
Rosaria Ignaccolo Jorge Mateu Ramon Giraldo 《Stochastic Environmental Research and Risk Assessment (SERRA)》2014,28(5):1171-1186
Functional data featured by a spatial dependence structure occur in many environmental sciences when curves are observed, for example, along time or along depth. Recently, some methods allowing for the prediction of a curve at an unmonitored site have been developed. However, the existing methods do not allow to include in a model exogenous variables that, for example, bring meteorology information in modeling air pollutant concentrations. In order to introduce exogenous variables, potentially observed as curves as well, we propose to extend the so-called kriging with external drift—or regression kriging—to the case of functional data by means of a three-step procedure involving functional modeling for the trend and spatial interpolation of functional residuals. A cross-validation analysis allows to choose smoothing parameters and a preferable kriging predictor for the functional residuals. Our case study considers daily PM10 concentrations measured from October 2005 to March 2006 by the monitoring network of Piemonte region (Italy), with the trend defined by meteorological time-varying covariates and orographical constant-in-time variables. The performance of the proposed methodology is evaluated by predicting PM10 concentration curves on 10 validation sites, even with simulated realistic datasets on a larger number of spatial sites. In this application the proposed methodology represents an alternative to spatio-temporal modeling but it can be applied more generally to spatially dependent functional data whose domain is not a time interval. 相似文献
70.
The paper aims at finding an RCM configuration that facilitates studies devoted to quantifying RCM response to parameter modification. When using short integration times, the response of the time-averaged variables to RCM modification tend to be blurred by the noise originating in the lack of predictability of the instantaneous atmospheric states. Two ways of enhancing the signal-to-noise ratio are studied in this work: spectral nudging and reduction of the computational domain size. The approach followed consists in the analysis of the sensitivity of RCM-simulated seasonal averages to perturbations of two parameters controlling deep convection and stratiform condensation, perturbed one at a time. Sensitivity is analyzed within different simulation configurations obtained by varying domain size and using the spectral nudging option. For each combination of these factors multiple members of identical simulations that differ exclusively in initial conditions are also generated to provide robust estimates of the sensitivities (the signal) and sample the noise. Results show that the noise magnitude is decreased both by reduction of domain size and the spectral nudging. However, the reduction of domain size alters some sensitivity signals. When spectral nudging is used significant alterations of the signal are not found. 相似文献