Precipitation and temperature space–time variability and extremes in the Mediterranean region: evaluation of dynamical and statistical downscaling methods     

Emmanouil Flaounas  Philippe Drobinski  Mathieu Vrac  Sophie Bastin  Cindy Lebeaupin-Brossier  Marc Stéfanon  Marco Borga  Jean-Christophe Calvet 《Climate Dynamics》2013,40(11-12):2687-2705

This study evaluates how statistical and dynamical downscaling models as well as combined approach perform in retrieving the space–time variability of near-surface temperature and rainfall, as well as their extremes, over the whole Mediterranean region. The dynamical downscaling model used in this study is the Weather Research and Forecasting (WRF) model with varying land-surface models and resolutions (20 and 50 km) and the statistical tool is the Cumulative Distribution Function-transform (CDF-t). To achieve a spatially resolved downscaling over the Mediterranean basin, the European Climate Assessment and Dataset (ECA&D) gridded dataset is used for calibration and evaluation of the downscaling models. In the frame of HyMeX and MED-CORDEX international programs, the downscaling is performed on ERA-I reanalysis over the 1989–2008 period. The results show that despite local calibration, CDF-t produces more accurate spatial variability of near-surface temperature and rainfall with respect to ECA&D than WRF which solves the three-dimensional equation of conservation. This first suggests that at 20–50 km resolutions, these three-dimensional processes only weakly contribute to the local value of temperature and precipitation with respect to local one-dimensional processes. Calibration of CDF-t at each individual grid point is thus sufficient to reproduce accurately the spatial pattern. A second explanation is the use of gridded data such as ECA&D which smoothes in part the horizontal variability after data interpolation and damps the added value of dynamical downscaling. This explains partly the absence of added-value of the 2-stage downscaling approach which combines statistical and dynamical downscaling models. The temporal variability of statistically downscaled temperature and rainfall is finally strongly driven by the temporal variability of its forcing (here ERA-Interim or WRF simulations). CDF-t is thus efficient as a bias correction tool but does not show any added-value regarding the time variability of the downscaled field. Finally, the quality of the reference observation dataset is a key issue. Comparison of CDF-t calibrated with ECA&D dataset and WRF simulations to local measurements from weather stations not assimilated in ECA&D, shows that the temporal variability of the downscaled data with respect to the local observations is closer to the local measurements than to ECA&D data. This highlights the strong added-value of dynamical downscaling which improves the temporal variability of the atmospheric dynamics with regard to the driving model. This article highlights the benefits and inconveniences emerging from the use of both downscaling techniques for climate research. Our goal is to contribute to the discussion on the use of downscaling tools to assess the impact of climate change on regional scales.  相似文献   

Dual-frequency ADCPs measuring turbidity     

Frédéric Jourdin  Caroline Tessier  Pierre Le Hir  Romaric Verney  Michel Lunven  Sophie Loyer  André Lusven  Jean-François Filipot  Jérémy Lepesqueur 《Geo-Marine Letters》2014,34(4):381-397

A pair of self-contained acoustic Doppler current profilers (SC-ADCPs) operating with different frequencies were moored on a muddy sea bottom at about 20 m depth in the Bay of Vilaine off the French Atlantic coast. With their acoustic beams oriented upwards, the SC-ADCPs ensonified most of the water column. The results of several months of in situ recorded echo intensity data spanning 2 years (2003 to 2004) from the dual-frequency ADCPs are presented in this paper. The aim was to estimate suspended particle mass concentration and mean size. A concentration index CI is proposed for the estimation of particle concentration. Based on theory the CI—unlike the volume backscatter strength—does not depend on particle size. Compared with in situ optical data, the CI shows reasonable precision but not increased with respect to that of the highest-frequency backscatter strength. Concerning the mean particle size, despite a lack of quantitative validation with optical particle-size measurements, the method yielded a qualitative discrimination of mineral (small) and organic (large) particles. This supports the potential of dual-frequency ADCPs to quantitatively determine particle size. A cross-calibration of the transducers of each ADCP shows that a specific component of the precision of the backscatter strength measured by ADCP depends on the acoustic frequency, the cell thickness and the ensemble integration time. Based on these results, the use of two ADCPs operating with distinctly different frequencies (two octaves apart) or a single dual-frequency ADCP is recommended.  相似文献   

The impact of ditch blocking on fluvial carbon export from a UK blanket bog          下载免费PDF全文

Christopher D. Evans  Michael Peacock  Sophie M. Green  Joseph Holden  Pippa J. Chapman  Inma Lebron  Nathan Callaghan  Richard Grayson  Andrew J. Baird 《水文研究》2018,32(13):2141-2154

We investigated the effects of ditch blocking on fluvial carbon concentrations and fluxes at a 5‐year, replicated, control‐intervention field experiment on a blanket peatland in North Wales, UK. The site was hydrologically instrumented, and run‐off via open and blocked ditches was analysed for dissolved organic carbon (DOC), particulate organic carbon, dissolved carbon dioxide, and dissolved methane. DOC was also analysed in peat porewater and overland flow. The hillslope experiment was embedded within a paired control‐intervention catchment study, with 3 years of preblocking and 6 years of postblocking data. Results from the hillslope showed large reductions in discharge via blocked ditches, with water partly redirected into hillslope surface and subsurface flows, and partly into remaining open ditches. We observed no impacts of ditch blocking on DOC, particulate organic carbon, dissolved carbon dioxide or methane in ditch waters, DOC in porewaters or overland flow, or stream water DOC at the paired catchment scale. Similar DOC concentrations in ditch water, overland flow, and porewater suggest that diverting flow from the ditch network to surface or subsurface flow had a limited impact on concentrations or fluxes of DOC entering the stream network. The subdued response of fluvial carbon to ditch blocking in our study may be attributable to the relatively low susceptibility of blanket peatlands to drainage, or to physical alterations of the peat since drainage. We conclude that ditch blocking cannot be always be expected to deliver reductions in fluvial carbon loss, or improvements in the quality of drinking water supplies.  相似文献   

Impacts of forest conversion and agriculture practices on water pathways in Southern Brazil          下载免费PDF全文

Jérémy Robinet  Jean P. G. Minella  Cláudia A. P. de Barros  Alexandre Schlesner  Andreas Lücke  Yolanda Ameijeiras-Mariño  Sophie Opfergelt  Jan Vanderborght  Gerard Govers 《水文研究》2018,32(15):2304-2317

Land‐use/cover change (LUCC), and more specifically deforestation and multidecadal agriculture, is one of the various controlling factors of water fluxes at the hillslope or catchment scale. We investigated the impact of LUCC on water pathways and stream stormflow generation processes in a subtropical region in southern Brazil. We monitored, sampled and analysed stream water, pore water, subsurface water, and rainwater for dissolved silicon concentration (DSi) and ¹⁸O/¹⁶O (δ¹⁸O) signature to identify contributing sources to the streamflow under forest and under agriculture. Both forested and agricultural catchments were highly responsive to rainfall events in terms of discharge and shallow groundwater level. DSi versus δ¹⁸O scatter plots indicated that for both land‐use types, two run‐off components contributed to the stream discharge. The presence of a dense macropore network, combined with the presence of a compact and impeding B‐horizon, led to rapid subsurface flow in the forested catchment. In the agricultural catchment, the rapid response to rainfall was mostly due to surface run‐off. A 2‐component isotopic hydrograph separation indicated a larger contribution of rainfall water to run‐off during rainfall event in the agricultural catchments. We attributed this higher contribution to a decrease in topsoil hydraulic conductivity associated with agricultural practices. The chemical signature of the old water component in the forested catchment was very similar to that of the shallow groundwater and the pore soil water: It is therefore likely that the shallow groundwater was the main source of old water. This is not the case in the agricultural catchments where the old water component had a much higher DSi concentration than the shallow groundwater and the soil pore water. As the agricultural catchments were larger, this may to some extent simply be a scale effect. However, the higher water yields under agriculture and the high DSi concentration observed in the old water under agriculture suggest a significant contribution of deep groundwater to catchment run‐off under agriculture, suggesting that LUCC may have significant effects on weathering rates and patterns.  相似文献   

Fast switch from extensional exhumation to thrusting of the Ronda Peridotites (South Spain)          下载免费PDF全文

Gianluca Frasca  Frédéric Gueydan  Marc Poujol  Jean‐Pierre Brun  Fleurice Parat  Patrick Monié  Alexandre Pichat  Sophie Mazier 《地学学报》2017,29(2):117-126

The Alboran Domain, situated at the western end of the Mediterranean subduction system, is characterized by the Ronda Peridotites, one of the world's largest exposures of sub‐continental mantle. Using U–Pb (LA‐ICP‐MS) and Ar–Ar dating, we precisely dated two tectonic events associated with the Tertiary exhumation of the Ronda Peridotites. First, shearing along the Crust–Mantle Extensional Shear Zone caused, at ca. 22.5 Ma, mantle exhumation, local partial melting in the deep crust and coeval cooling in the upper crust. Second, the Ronda Peridotites Thrust triggered the final emplacement of the peridotites onto the continental crust at c. 21 Ma, as testified by granitic intrusions in the thrust hangingwall. The tectonic evolution of the western Alboran Domain is therefore characterized by a fast switch from continental lithospheric extension in a backarc setting, with sub‐continental mantle exhumation, to a rift inversion by thrusting driven by shortening of the upper plate.  相似文献   

Bayesian estimation of intensity–duration–frequency curves and of the return period associated to a given rainfall event     

David Huard  Alain Mailhot  Sophie Duchesne 《Stochastic Environmental Research and Risk Assessment (SERRA)》2010,24(3):337-347

Intensity–duration–frequency (IDF) curves are used extensively in engineering to assess the return periods of rainfall events and often steer decisions in urban water structures such as sewers, pipes and retention basins. In the province of Québec, precipitation time series are often short, leading to a considerable uncertainty on the parameters of the probabilistic distributions describing rainfall intensity. In this paper, we apply Bayesian analysis to the estimation of IDF curves. The results show the extent of uncertainties in IDF curves and the ensuing risk of their misinterpretation. This uncertainty is even more problematic when IDF curves are used to estimate the return period of a given event. Indeed, standard methods provide overly large return period estimates, leading to a false sense of security. Comparison of the Bayesian and classical approaches is made using different prior assumptions for the return period and different estimation methods. A new prior distribution is also proposed based on subjective appraisal by witnesses of the extreme character of the event.  相似文献   

Global implementation of marine protected areas: Is the developing world being left behind?     

Sophie Marinesque  David M. Kaplan 《Marine Policy》2012,36(3):727-737

While the global network of marine protected areas (MPAs) has recently been evaluated in the light of bio-geographic targets, there has been no attempt to evaluate the relative conservation efforts made by the different nations with regards to their level of socio-economic development. Using information mostly gathered from the world database on protected areas (WDPA), this paper gives a comparative assessment of MPA progress in countries from different economic categories, ranging from advanced economies to least developed countries (LDCs). Potentially explanatory socio-economic and environmental factors, such as fishing activity and existence of vulnerable marine ecosystems, for variability between nations in the level of MPA implementation are also explored. Existing MPA databases demonstrate a clear gap between developed and developing nations in MPA establishment, with advanced economies accounting for two thirds of the global MPA network. Patterns of MPA use, however, remain extremely heterogeneous between countries within each development group. International agreements on marine conservation, above and beyond the influence of country socio-economic and environmental profiles, are identified as a stimulating factor to MPA implementation. The level dependence on marine resource extraction appears to impede MPA implementation, though the relationship is not statistically significant due to large heterogeneity among countries. Leading developed nations increasingly use MPAs to designate integrated and adaptive management areas, and implementation of large “no-take” reserves in relatively-pristine overseas areas continues to accelerate. These analyses highlight certain limitations regarding our ability to assess the true conservation effectiveness of the existing global MPA network and the need for improved indicators of MPA restrictions and management efforts.  相似文献   

Studying interactions between excavating sponges and massive corals by the use of hybrid cores          下载免费PDF全文

James K. H. Fang  Robert A. B. Mason  Christine H. L. Schönberg  Ove Hoegh‐Guldberg  Sophie Dove 《Marine Ecology》2017,38(1)

Excavating sponges often compete with reef‐building corals. To study sponge–coral interactions, we devised a design of hybrid cores that allows sponges and corals to be arranged side by side with similar size and shape, mimicking the situation of neighbouring organisms. Compared to earlier methods that attached sponge cores onto coral surfaces, hybrid cores provide an opportunity to study organism interactions under conditions more equal to the interacting partners. The use of hybrid cores was demonstrated for the excavating sponge Cliona orientalis and the massive coral Porites, which commonly interact on the Great Barrier Reef. Cliona orientalis and massive Porites were cut into half‐moon shaped explants and combined as hybrid cores under replicate conditions. After 90 days in an aquarium setting, positive growth of Cl. orientalis along with net bioerosion were observed in sponge control cores that combined Cl. orientalis with blank substrate. However, when Cl. orientalis and massive Porites were in contact in interaction cores, the sponge displayed negative growth and undetectable bioerosion, and was slightly overgrown by the coral. Cliona orientalis may have developed tissue extension beneath the living coral tissue, but growth and net calcification rates of massive Porites were apparently not affected by Cl. orientalis when comparing the interaction cores to coral control cores that combined massive Porites with blank substrate. Overall, the present work demonstrated that hybrid cores can be used to generate conditions suitable for studying sponge–coral interactions in the laboratory, which can also be applied in the field.  相似文献   

Methods to quantify components of the excavating sponge Cliona orientalis Thiele, 1900     

James K. H. Fang  Christine H. L. Schönberg  David I. Kline  Ove Hoegh‐Guldberg  Sophie Dove 《Marine Ecology》2013,34(2):193-206

This study applied the loss after combustion (LAC) method and the acid decalcification (ADC) method to quantify different components of an excavating sponge. Samples of dried coral skeleton of Favia sp. invaded by the Indo‐Pacific excavating sponge Cliona orientalis Thiele, 1900 were used. The sponge tissue penetrated the 12‐mm‐thick samples to approximately 10 mm. The average proportional weight of organic matter, siliceous spicules, calcareous substrate and salts in the entire samples was found to be respectively 2.5%, 4.4%, 90.5% and 2.5% of dry weight applying the LAC method, and 2.9%, 5.9%, 89.0% and 2.3% of dry weight applying the ADC method. Respective volumetric proportions of the organic matter, spicules, substrate and salts were then calculated to be 6.4%, 5.5%, 85.2% and 3.0% of volume with the LAC method, and 7.4%, 7.2%, 82.7% and 2.7% of volume with the ADC method. The LAC method showed low variability of data and is simple and fast and therefore is recommended. The ADC method generated very similar results to the LAC method. However, due to the handling involved in the ADC method, more than half of the spicules may be lost and the method is therefore not recommended unless careful data corrections are considered. In addition, the buoyant weight method was used to quantify actual substrate weight in the fresh sponge‐substrate samples. This method was found to be at least 97% effective, revealing that buoyant weights can potentially be used to quantify bioerosion rates of excavating sponges. To our knowledge, this is the first study to systemically quantify organic and inorganic components of an excavating sponge and its calcareous substrate, providing improved standard methods for future studies.  相似文献   

Improving vertical GPS precision with a GPS-over-fiber architecture and real-time relative delay calibration   总被引：2，自引：0，他引：2  

Daniel Macias-Valadez  Rock Santerre  Sophie Larochelle  René Landry Jr. 《GPS Solutions》2012,16(4):449-462

A limitation of GPS positioning is that the vertical component is generally two to three times less precise than the horizontal components. In a previous work by R. Santerre of Laval University and G. Beutler of University of Bern, it was shown in simulations that it is possible to improve the GPS vertical positioning precision by using a multi-antenna GPS receiver and a precise calibration technique of the relative hardware delay between the antennas and the receiver. However, no actual implementation of the system was done to prove the concept until now. A new multi-antenna, GPS-over-fiber architecture with real-time delay monitoring, designed and implemented to improve the vertical precision is presented. The improvement in vertical precision arises from the elimination of the relative receiver clock error in single difference, between antennas, and the precision real-time calibration of the relative hardware delay. Experiments were conducted with a zero baseline and a short baseline configuration. The results show, as expected by the theory and the simulations, a two to three times improvement in the precision of the vertical component such that it reached the same level of performance as the horizontal components. These promising results will enable the use of this type of configuration in several applications where the same precision in all 3D components is essential and could not be achieved before with standard GPS positioning techniques.  相似文献