End member and Bayesian mixing models consistently indicate near-surface flowpath dominance in a pristine humid tropical rainforest     

Christian Birkel  Alicia Correa Barahona  Clément Duvert  Sebastián Granados Bolaños  Andres Chavarría Palma  Ana Maria Durán Quesada  Ricardo Sánchez Murillo  Harald Biester 《水文研究》2021,35(4):e14153

The impacts of forest conversion on runoff generation in the tropics have received much interest, but scientific progress is still hampered by challenging fieldwork conditions and limited knowledge about runoff mechanisms. Here, we assessed the runoff generation, flow paths and water source dynamics of a pristine rainforest catchment in Costa Rica using end member mixing analysis (EMMA) and a Bayesian mixing model (MixSIAR). Geochemical tracer data collected over a 4-week field campaign were combined with tritium data used to assess potential deeper groundwater flow pathways to the perennial stream. The streamflow composition was best captured using three end-members, namely throughfall, shallow (5–15 cm) and deeper (15–50 cm) soil water. We estimated the end-member contributions to the main stream and two tributaries using the two mixing approaches and found good agreement between results obtained from EMMA and MixSIAR. The system was overwhelmingly dominated by near-surface sources, with little evidence for deeper and older groundwater as tritium-derived baseflow mean transit time was between 2.0 and 4.4 years. The shallow soil flow pathway dominated streamflow contributions in the main stream (median 39% and 49% based on EMMA and MixSIAR, respectively), followed by the deeper soil (32% and 31%) and throughfall (25% and 19%). The two tributaries had even greater shallow soil water contributions relative to the main stream (83% and 74% for tributary A and 42% and 63% for tributary B). Tributary B had no detectable deep soil water contribution, reflecting the morphology of the hillslope (steeper slopes, shallower soils and lower vegetation density compared to hillslope A). Despite the short sampling campaign and associated uncertainties, this study allowed to thoroughly assess runoff generation mechanisms in a humid tropical catchment. Our results also provide a first comparison of two increasingly used mixing models and suggest that EMMA and MixSIAR yield comparable estimates of water source partitioning in this tropical, volcanic rainforest environment.  相似文献   

AUS: Anisotropic undrained shear strength model for clays     

Kristian Krabbenhøft  Sergio Andres Galindo-Torres  Xue Zhang  Jørgen Krabbenhøft 《国际地质力学数值与分析法杂志》2019,43(17):2652-2666

A total stress model applicable to clays under undrained conditions is presented. The model involves three strength parameters: the undrained shear strengths in triaxial compression, triaxial extension, and simple shear. The amount of physical anisotropy implied by the model is a function of the relative magnitude of these three strengths assuming a Mises-type plastic potential. Elastoplastic deformation characteristics below failure are accounted for by a hardening law requiring two additional parameters that can be related to the axial strains halfway to failure in triaxial compression and extension. Finally, elasticity is accounted for by Hooke law. The result is a relatively simple model whose parameters can all be inferred directly from a combination of in situ and standard undrained laboratory tests. The model is applied to a problem involving the horizontal loading of a monopile foundation for which full scale tests have been previously conducted. The model shows good agreement with the measured data.  相似文献   

Modelling changes in suspended sediment from forest road surfaces in a coastal watershed of British Columbia          下载免费PDF全文

H. Andres Araujo  Ashley Page  Andrew B. Cooper  Jeremy Venditti  Erland MacIsaac  Marwan A. Hassan  Duncan Knowler 《水文研究》2014,28(18):4914-4927

Erosion from logging road surfaces, cut slopes, banks, and ditches represents a chronic source of sediment input to streams that can degrade aquatic habitats. Road surface erosion is of particular concern because the magnitude of sediment generation when traffic levels are high can be large. Current models for predicting sediment production from roads require information on area‐specific sediment delivery, which is not often available. Here, we developed a model to quantify suspended sediment concentrations (SSC) generated by forest roads surfaces under different conditions of use and density. This model is designed for a typical medium‐size coastal watershed of British Columbia or the American Pacific Northwest, and was applied to the Chilliwack River watershed as a case study. The results illustrate that intensive use of forest roads combined with high road density can increase the number of extreme sedimentation events over a predetermined threshold. A comparison of the effects of road density and the level of road use suggests that the level of road use is more important than the road density for the generation of fine sediment from road surfaces. However, the model omits the impact of roads on mass movements in a watershed, which represent a major source of sediment in steep watersheds, so the effect of road density is likely more substantial than the model predicts. The model is an attempt to overcome field data limitations by using an empirical relation between SSC and traffic variables, and presents a starting point for more intensive field studies that could be used to validate it. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Is the forest conversion to pasture affecting the hydrological response of Amazonian catchments? Signals in the Ji‐Paraná Basin     

Daniel Andres Rodriguez  Javier Tomasella  Claudia Linhares 《水文研究》2010,24(10):1254-1269

  相似文献   

FDE index for goodness‐of‐fit between measured and calculated response signals     

Jeff J. Dragovich  Andres Lepage 《地震工程与结构动力学》2009,38(15):1751-1758

A method is presented for determining the goodness‐of‐fit between measured and calculated structural response signals. The method is termed as the frequency domain error (FDE) index, which is a value between 0 and 1 where zero indicates a perfect correlation. The FDE is calculated from the Fourier spectra of the measured and calculated waveforms, using a relatively simple calculation procedure, readily implemented using standard fast Fourier transform (FFT) libraries. The FDE is demonstrated herein using three different types of problems: simple harmonic waves, a large number of earthquake response simulations, and a set of limited simulations. Along with the FDE concept, effective methods for displaying the results are presented. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

A multi-physics ensemble of regional climate change projections over the Iberian Peninsula     

Sonia Jerez  Juan Pedro Montavez  Juan Jose Gomez-Navarro  Raquel Lorente-Plazas  Juan Andres Garcia-Valero  Pedro Jimenez-Guerrero 《Climate Dynamics》2013,41(7-8):1749-1768

This study illustrates the sensitivity of regional climate change projections to the model physics. A single-model (MM5) multi-physics ensemble of regional climate simulations over the Iberian Peninsula for present (1970–1999) and future (2070–2099 under the A2 scenario) periods is assessed. The ensemble comprises eight members resulting from the combination of two options of parameterization schemes for the planetary boundary layer, cumulus and microphysics. All the considered combinations were previously evaluated by comparing hindcasted simulations to observations, none of them providing clearly outlying climates. Thus, the differences among the various ensemble members (spread) in the future projections could be considered as a matter of uncertainty in the change signals (as similarly assumed in multi-model studies). The results highlight the great dependence of the spread on the synoptic conditions driving the regional model. In particular, the spread generally amplifies under the future scenario leading to a large spread accompanying the mean change signals, as large as the magnitude of the mean projected changes and analogous to the spread obtained in multi-model ensembles. Moreover, the sign of the projected change varies depending on the choice of the model physics in many cases. This, together with the fact that the key mechanisms identified for the simulation of the climatology of a given period (either present or future) and those introducing the largest spread in the projected changes differ significantly, make further claims for efforts to better understand and model the parameterized subgrid processes.  相似文献   

Introduction to the Wood in World Rivers special issue     

Ellen Wohl  Andres Iroumé 《地球表面变化过程与地形》2021,46(9):1640-1645

  相似文献   

Streamwise Versus Spanwise Spacing of Obstacle Arrays: Parametrization of the Effects on Drag and Turbulence     

Andres Simón-Moral  Jose Luis Santiago  E. Scott Krayenhoff  Alberto Martilli 《Boundary-Layer Meteorology》2014,151(3):579-596

A Reynolds-averaged Navier–Stokes model is used to investigate the evolution of the sectional drag coefficient and turbulent length scales with the layouts of aligned arrays of cubes. Results show that the sectional drag coefficient is determined by the non-dimensional streamwise distance (sheltering parameter), and the non-dimensional spanwise distance (channelling parameter) between obstacles. This is different than previous approaches that consider only plan area density $(\lambda _\mathrm{p})$ . On the other hand, turbulent length scales behave similarly to the staggered case (e. g. they are function of $\lambda _\mathrm{p}$ only). Analytical formulae are proposed for the length scales and for the sectional drag coefficient as a function of sheltering and channelling parameters, and implemented in a column model. This approach demonstrates good skill in the prediction of vertical profiles of the spatially-averaged horizontal wind speed.  相似文献   

Impacts of landscape fragmentation on simulated precipitation fields in the Amazonian sub-basin of Ji-Paraná using the Eta model     

Daniel Andres Rodriguez  Sin Chan Chou  Javier Tomasella  Eleonora M. C. Demaria 《Theoretical and Applied Climatology》2014,115(1-2):121-140

Numerical studies on impacts of landscape fragmentation due to land use and land cover change (LUCC) on precipitation fields over the Ji-Paraná basin in the Amazon region are carried out using atmospheric Eta model. Experiments consider historical data about LUCC over the basin from 1978 to 2000 and compare simulations under LUCC conditions with simulations under pristine conditions. In agreement with previous observational studies, model results do not show statistically significant impacts on precipitation in the region. Results indicate that variability in precipitation in this region is mainly controlled by large-scale atmospheric characteristics and soil moisture conditions. However, some limitations are identified in the model simulations, mainly associated to the diurnal cycle of precipitation.  相似文献   

(Near-)real-time orbit determination for GNSS radio occultation processing   总被引：2，自引：1，他引：1  

Oliver Montenbruck  André Hauschild  Yago Andres  Axel von Engeln  Christian Marquardt 《GPS Solutions》2013,17(2):199-209

The processing of GPS radio occultation measurements for use in numerical weather predictions requires a precise orbit determination (POD) of the host satellite in near-real-time. Making use of data from the GRAS instrument on Metop-A, the performance of different GPS ephemeris products and processing concepts for near-real-time and real-time POD is compared. While previous analyses have focused on the achievable along-track velocity accuracy, this study contributes a systematic comparison of the resulting estimated bending angles. This enables a more rigorous trade-off of different orbit determination methodologies in relation to the end-user needs for atmospheric science products. It is demonstrated that near-real-time GPS orbit and clock products have reached a sufficient quality to determine the Metop-A along-track velocity with an accuracy of better than 0.05 mm/s that was formerly only accessible in post-processing. The resulting bending angles are shown to exhibit standard deviation and bias differences of less than 0.3 % compared with post-processed products up to altitudes of at least 40 km, which is notably better than 1 % accuracy typically assumed for numerical weather predictions in this height regime. Complementary to the analysis of ground-based processing schemes, the potential of autonomous on-board orbit determination is investigated for the first time. Using actual GRAS flight data, it is shown that a 0.5 m 3D rms position accuracy and a 0.2 mm/s along-track velocity accuracy can in fact be obtained in real-time with the currently available GPS broadcast ephemeris quality. Bending angles derived from the simulated real-time processing exhibit a minor performance degradation above tangent point heights of 40 km but negligible differences with respect to ground-based products below this altitude. Onboard orbit determination and, if desired, bending angle computation, can thus enable a further simplification of the ground segment in future radio occultation missions and contribute to reduced product latencies for radio occultation data assimilation in numerical weather predictions.  相似文献