Copula models for frequency analysis what can be learned from a Bayesian perspective?     

《Advances in water resources》2014

Large spring floods in the Québec region exhibit correlated peakflow, duration and volume. Consequently, traditional univariate hydrological frequency analyses must be complemented by multivariate probabilistic assessment to provide a meaningful design flood level as requested in hydrological engineering (based on return period evaluation of a single quantity of interest). In this paper we study 47 years of a peak/volume dataset for the Romaine River with a parametric copula model. The margins are modeled with a normal or gamma distribution and the dependence is depicted through a parametric family of copulas (Arch 12 or Arch 14). Parameter joint inference and model selection are performed under the Bayesian paradigm. This approach enlightens specific features of interest for hydrological engineering: (i) cross correlation between margin parameters are stronger than expected , (ii) marginal distributions cannot be forgotten in the model selection process and (iii) special attention must be addressed to model validation as far as extreme values are of concern.  相似文献   

First-principles derivation of reactive transport modeling parameters for particle tracking and PDE approaches     

《Advances in water resources》2014

Both Eulerian and Lagrangian reactive transport simulations in natural media require selection of a parameter that controls the “promiscuity” of the reacting particles. In Eulerian models, measurement of this parameter may be difficult because its value will generally differ between natural (diffusion-limited) systems and batch experiments, even though both are modeled by reaction terms of the same form. And in Lagrangian models, there previously has been no a priori way to compute this parameter. In both cases, then, selection is typically done by calibration, or ad hoc. This paper addresses the parameter selection problem for Fickian transport by deriving, from first principles and D (the diffusion constant) the reaction-rate-controlling parameters for particle tracking (PT) codes and for the diffusion–reaction equation (DRE). Using continuous time random walk analysis, exact reaction probabilities are derived for pairs of potentially reactive particles based on D and their probability of reaction provided that they collocate. Simultaneously, a second PT scheme directly employing collocation probabilities is derived. One-to-one correspondence between each of D, the reaction radius specified for a PT scheme, and the DRE decay constant are then developed. These results serve to ground reactive transport simulations in their underlying thermodynamics, and are confirmed by simulations.  相似文献   

Characterization of error dynamics in a 3D coastal model of the Catalan sea using stochastic modelling     

Gabriel Jordà  Pierre De Mey 《Continental Shelf Research》2010

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Understanding of the Common Land Model performance for water and energy fluxes in a farmland during the growing season in Korea   总被引：1，自引：0，他引：1  

Minha Choi  Seung Oh Lee  Hyojung Kwon 《水文研究》2010,24(8):1063-1071

The Common Land Model (CLM) is one of the most widely used land surface models (LSMs) due to the practicality of its simple parameterization scheme and its versatility in embracing a variety of field datasets. The improved assessment of land surface water and energy fluxes using CLM can be an alternative approach for understanding the complex land–atmosphere interactions in data‐limited regions. The understanding of water and energy cycles in a farmland is crucial because it is a dominant land feature in Korea and Asia. However, the applications of CLM to farmland in Korea are in paucity. The simulations of water and energy fluxes by CLM were conducted against those from the tower‐based measurements during the growing season of 2006 at the Haenam site (a farmland site) in Korea without optimization. According to the International Geosphere–Biosphere Programme (IGBP) land cover classification, a homogeneous cropland was selected initially for this study. Although the simulated soil moisture had a similar pattern to that of the observed, the former was relatively drier (at 0·1 m³ m^?3) than the latter. The simulated net radiation showed good agreement with the observed, with a root mean squared error (RMSE) of 41 W m^?2, whereas relatively large discrepancies between the simulation and observation were found in sensible (RMSE of 66 W m^?2) and latent (RMSE of 60 W m^?2) heat fluxes. On the basis of the sensitivity analysis, soil moisture was more receptive to land cover and soil texture parameterizations when compared to soil temperature and turbulent fluxes. Despite the uncertainty in the predictive capability of CLM employed without optimization, the initial performance of CLM suggests usefulness in a data‐limited heterogeneous farmland in Korea. Further studies are required to identify the controls on water and energy fluxes with an improved parameterization. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Global Plate Motions and Their Impact on the Earth''s Surface Area Change     

Cao Shuai  Zhang Keliang  Wei Dongping 《中国地震研究》2010,24(3):344-352

Based on their Euler poles,we calculated the relative velocities between every two plates in the typical global plate motion models,respectively,and estimated the area change along these boundaries. In our calculations,plates on both sides accommodated area changes depending on the boundary types: extensional, convergent or transform, so we can estimate area change of each plate and then globally. Our preliminary results show that the area of the southern hemisphere increased while that of the northern hemisphere decreased over the past 1 million years,and global area has increased by 26,000km2 to 36,000km2,which corresponds to the 160m～250m increment on the Earth's radius if all these area increments are attributed to Earth's expansion. Taking the NUVEL-1 model as an example,of the 14 plates in this model,11 are decreasing,but the global area has increased because of the larger increment amount from Africa,North America and Antarctica. Finally,we also discussed factors affecting the global area change such as subduction zone retreating and back-arc spreading.  相似文献   

Estimating uncertainty associated with water stages from a single SAR image     

Guy Schumann  Florian Pappenberger  Patrick Matgen 《Advances in water resources》2008

It is the goal of remote sensing to infer information about objects or a natural process from a remote location. This invokes that uncertainty in measurement should be viewed as central to remote sensing. In this study, the uncertainty associated with water stages derived from a single SAR image for the Alzette (G.D. of Luxembourg) 2003 flood is assessed using a stepped GLUE procedure. Main uncertain input factors to the SAR processing chain for estimating water stages include geolocation accuracy, spatial filter window size, image thresholding value, DEM vertical precision and the number of river cross sections at which water stages are estimated. Initial results show that even with plausible parameter values uncertainty in water stages over the entire river reach is 2.8 m on average. Adding spatially distributed field water stages to the GLUE analysis following a one-at-a-time approach helps to considerably reduce SAR water stage uncertainty (0.6 m on average) thereby identifying appropriate value ranges for each uncertain SAR water stage processing factor. For the GLUE analysis a Nash-like efficiency criterion adapted to spatial data is proposed whereby acceptable SAR model simulations are required to outperform a simpler regression model based on the field-surveyed average river bed gradient. Weighted CDFs for all factors based on the proposed efficiency criterion allow the generation of reliable uncertainty quantile ranges and 2D maps that show the uncertainty associated with SAR-derived water stages. The stepped GLUE procedure demonstrated that not all field data collected are necessary to achieve maximum constraining. A possible efficient way to decide on relevant locations at which to sample in the field is proposed. It is also suggested that the resulting uncertainty ranges and flood extent or depth maps may be used to evaluate 1D or 2D flood inundation models in terms of water stages, depths or extents. For this, the extended GLUE approach, which copes with the presence of uncertainty in the observed data, may be adopted.  相似文献   

Accounting for model error in risk assessments: Alternatives to adopting a bias towards conservative risk estimates in decision models     

Petros Gaganis  Leslie Smith 《Advances in water resources》2008

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月表有效太阳辐照度实时模型   总被引：2，自引：0，他引：2       下载免费PDF全文

李雄耀  王世杰  程安云 《地球物理学报》2008,51(1):25-30

月表太阳辐射是深入研究月表温度分布的关键问题之一. 本文根据月表有效太阳辐照度与太阳常数、太阳辐射入射角以及日月距离之间的关系,建立月表有效太阳辐照度的实时模型. 该模型在1950～2050年的100年内的理论误差百分比小于0.28％, 相对前人提出的模型在精度上有了很大程度的提高,能较为真实地反映月表有效太阳辐照度随时间的变化规律. 计算结果表明2007年月表太阳辐照度的年变化范围在1321.5～1416.6 W·m^-2之间,平均为1368.0 W·m^-2. 通过对月表太阳辐射入射角计算结果的分析,证实了月球的两极可能存在极昼极夜.  相似文献   

岩溶水作用下填石路基稳定性模型试验研究   总被引：2，自引：2，他引：0  

蒋小珍  雷明堂  李瑜  戴建玲  蒙彦 《中国岩溶》2005,24(2):96-102

以广西水南高速为工程依托点,通过大型岩溶塌陷物理模型试验室,针对岩溶区填石路基中不同岩溶形态的处置方式,模拟研究岩溶水对填石路基的稳定性问题。试验中,重点研究了四种结构: 填石级配型、(片石+ 级配碎石+ 土工布+填石)型、反滤层型、(土+ 填石)型,它们分别对应岩溶水对填石路基侵蚀问题及填石路基的稳定性问题,漏斗、落水洞的处理及土工布防止细粒土流失引起路基变形问题,溶洞填充物的流失问题,岩溶水对粘土路基潜蚀问题及石牙地基的处理。试验结果表明,地下水位变化的瞬时速度对填石路基的稳定性具有重要意义,不同的处置方法在抵抗地下水冲刷方面有显著区别。   相似文献   

盘锦湿地芦苇叶片气孔导度的模拟   总被引：8，自引：0，他引：8       下载免费PDF全文

周莉  周广胜  贾庆宇  吕国红  谢艳兵  赵先丽 《气象与环境学报》2006,22(4):42-46

基于2005年5～9月盘锦湿地芦苇叶片气体交换观测数据,针对芦苇叶片气孔导度与光合速率以及光合速率与光合有效辐射之间的关系进行分析。结果表明:芦苇叶片气孔导度与光合速率的关系可应用Ball-Berry模型描述,光合速率与光合有效辐射的关系可应用非直角双曲线光合模型描述,联合Ball-Berry模型与非直角双曲线光合模型可通过环境变量求解叶片气孔导度。模型考虑了气孔导度与光合之间的相互作用。利用实验数据对气孔导度模型验证表明,叶片气孔导度模拟值和观测值回归方程的斜率为0.95,方程决定系数R=0.82(P<0.05)。  相似文献