Model Uncertainty Representation for a Convection-Allowing Ensemble Prediction System Based on CNOP-P

Formulating model uncertainties for a convection-allowing ensemble prediction system(CAEPS) is a much more challenging problem compared to well-utilized approaches in synoptic weather forecasting. A new approach is proposed and tested through assuming that the model uncertainty should reasonably describe the fast nonlinear error growth of the convection-allowing model, due to the fast developing character and strong nonlinearity of convective events. The Conditional Nonlinear Optimal Perturbation related to Parameters(CNOP-P) is applied in this study. Also, an ensemble approach is adopted to solve the CNOP-P problem. By using five locally developed strong convective events that occurred in pre-rainy season of South China, the most sensitive parameters were detected based on CNOP-P, which resulted in the maximum variations in precipitation. A formulation of model uncertainty is designed by adding stochastic perturbations into these sensitive parameters. Through comparison ensemble experiments by using all the 13 heavy rainfall cases that occurred in the flood season of South China in 2017, the advantages of the CNOP-P-based method are examined and verified by comparing with the well-utilized stochastically perturbed physics tendencies(SPPT) scheme. The results indicate that the CNOP-P-based method has potential in improving the under-dispersive problem of the current CAEPS.     

分光光度法测定钼矿石中钼不确定度评定

对分光光度法测定钼矿石中钼质量分数的不确定度进行评估,建立了数学模型,评定测量过程中不确定度主要来源于曲线拟合,以及重复实验产生的不确定度。当矿石中钼质量分数为0.054%时,评定其扩展不确定度为0.003 0%（k=2）。     

气候变化下水文极端事件变化预测研究进展

全球气候变化对洪水、干旱等极端水文事件的影响已成为一个亟待解决的科学问题.针对国内外在气候变化下采用统计降尺度和降雨径流模型对水文极端事件进行预测的研究进展进行了系统分析,在分类阐述的基础上,总结了国内外最新的研究进展及在预估过程中存在的问题和解决方案,试图凝练出一些气候变化背景下水文极端事件预估的新思路.结果表明:为有效降低极端水文事件预估的不确定性,各种集合模拟技术、数据同化方法、强化观测技术及水文模型的尺度转换理论将是有效的解决途径.     

Nash model parameter uncertainty analysis by AM-MCMC based on BFS and probabilistic flood forecasting

A hydrologic model consists of several parameters which are usually calibrated based on observed hydrologic processes. Due to the uncertainty of the hydrologic processes, model parameters are also uncertain, which further leads to the uncertainty of forecast results of a hydrologic model. Working with the Bayesian Forecasting System (BFS), Markov Chain Monte Carlo simulation based Adaptive Metropolis method (AM-MCMC) was used to study parameter uncertainty of Nash model, while the probabilistic flood forecasting was made with the simulated samples of parameters of Nash model. The results of a case study shows that the AM-MCMC based on BFS proposed in this paper is suitable to obtain the posterior distribution of the parameters of Nash model according to the known information of the parameters. The use of Nash model and AM-MCMC based on BFS was able to make the probabilistic flood forecast as well as to find the mean and variance of flood discharge, which may be useful to estimate the risk of flood control decision.     

长三角地区旅游城市体系组织秩序信息维数研究

对长三角地区旅游城市体系的旅游功能进行量化处理,采用分形方法研究其组织秩序来考察旅游城市体系对旅游活动的支撑作用,通过对长三角旅游城市体系组织秩序的信息维数的测算与分析,认为长三角地区旅游城市体系组织秩序具有较好的分形特征,系统结构比较紧致,各城市之间的整体性较好,对旅游活动的支撑作用较强.无论北部子系统还是南部子系统,上海在其体系中均具有很强的中心辐射作用,但也存在一定的差异,上海市对南部旅游城市体系旅游功能的加强程度要高于其在北部旅游城市体系中的作用.在目前条件下,上海还不足以带动整个长三角地区旅游城市体系整体性的提高,因此,加强上海的中心辐射作用,是使之成为实现长三角旅游城市一体化程度提高的重要途径.     

Impact of time-scale of the calibration objective function on the performance of watershed models

Many of the continuous watershed models perform all their computations on a daily time step, yet they are often calibrated at an annual or monthly time-scale that may not guarantee good simulation performance on a daily time step. The major objective of this paper is to evaluate the impact of the calibration time-scale on model predictive ability. This study considered the Soil and Water Assessment Tool for the analyses, and it has been calibrated at two time-scales, viz. monthly and daily for the War Eagle Creek watershed in the USA. The results demonstrate that the model's performance at the smaller time-scale (such as daily) cannot be ensured by calibrating them at a larger time-scale (such as monthly). It is observed that, even though the calibrated model possesses satisfactory ‘goodness of fit’ statistics, the simulation residuals failed to confirm the assumption of their homoscedasticity and independence. The results imply that evaluation of models should be conducted considering their behavior in various aspects of simulation, such as predictive uncertainty, hydrograph characteristics, ability to preserve statistical properties of the historic flow series, etc. The study enlightens the scope for improving/developing effective autocalibration procedures at the daily time step for watershed models. Copyright © 2007 John Wiley & Sons, Ltd.     

不确定条件下的定价模型及比较

就需求、成本不确定性的一般情况，建立了基于期望利润最大化的一般定价模型，并就4种特殊定价模型，在不确定性条件下，对垄断厂商采用确定性定价与采用不确定性定价下的收益及最优产量等情况进行了比较，为垄断者在定价时提供参考。     

一种订货带有折扣的库存-生产模型的优化分析

建立了由一个仓库和一个加工车间组成的库存-加工系统模型,该模型具有随机的需求过程和随机的供货时间.在假设允许缺货,订货带有批量折扣,并采用(s,S)库存策略的条件下,用排队论得到了该系统的无穷小生成元,给出了系统的费用函数,并对库存策略进行了优化分析.     

Separation of base flow from streamflow using groundwater levels—illustrated for the Pang catchment (UK)

A new filter to separate base flow from streamflow has developed that uses observed groundwater levels. To relate the base flow to the observed groundwater levels, a non‐linear relation was used. This relation is suitable for unconfined aquifers with deep groundwater levels that do not respond to individual rainfall event. Because the filter was calibrated using total streamflow, an estimate of the direct runoff was also needed. The direct runoff was estimated from precipitation and potential evapotranspiration using a water balance model. The parameters for the base flow and direct runoff were estimated simultaneously using a Monte Carlo approach. Instead of one best solution, a range of satisfactory solutions was accepted. The filter was applied to data from two nested gauging stations in the Pang catchment (UK). Streamflow at the upstream station (Frilsham) is strongly dominated by base flow from the main aquifer, whereas at the downstream station (Pangbourne) a significant component of direct runoff also occurs. The filter appeared to provide satisfactory estimates at both stations. For Pangbourne, the rise of the base flow was strongly delayed compared with the rise of the streamflow. However, base flow exceeded streamflow on several occasions, especially during summer and autumn, which might be explained by evapotranspiration from riparian vegetation. To evaluate the results, the base flow was also estimated using three existing base‐flow separation filters: an arithmetic filter (BFI), a digital filter (Boughton) and another filter based on groundwater levels (Kliner and Knĕz̆ek). Both the BFI and Boughton filters showed a much smaller difference in base flow between the two stations. The Kliner and Knĕz̆ek filter gave consistently lower estimates of the base flow. Differences and lack of clarity in the definition of base flow complicated the comparison between the filters. An advantage of the method introduced in this paper is the clear interpretation of the separated components. A disadvantage is the high data requirement. Copyright © 2004 John Wiley & Sons, Ltd.     

Hydrological heterogeneity of an alpine stream–lake network in Switzerland

Water source and lake landscape position can strongly influence the physico‐chemical characteristics of flowing waters over space and time. We examined the physico‐chemical heterogeneity in surface waters of an alpine stream‐lake network (>2600 m a.s.l.) in Switzerland. The catchment comprises two basins interspersed with 26 cirque lakes. The larger lakes in each basin are interconnected by streams that converge in a lowermost lake with an outlet stream. The north basin is primarily fed by precipitation and groundwater, whereas the south basin is fed mostly by glacial melt from rock glaciers. Surface flow of the entire channel network contracted by ～60% in early autumn, when snowmelt runoff ceased and cold temperatures reduced glacial outputs, particularly in the south basin. Average water temperatures were ～4 °C cooler in the south basin, and temperatures increased by about 4–6 °C along the longitudinal gradient within each basin. Although overall water conductivity was low (<27 µS cm^?1) because of bedrock geology (ortho‐gneiss), the south basin had two times higher conductivity values than the north basin. Phosphate‐phosphorus levels were below analytical detection limits, but particulate phosphorus was about four times higher in the north basin (seasonal average: 9 µg l^?1) than in the south basin (seasonal average: 2 µg l^?1). Dissolved nitrogen constituents were around two times higher in the south basin than in the north basin, with highest values averaging > 300 µg l^?1 (nitrite + nitrate‐nitrogen), whereas particulate nitrogen was approximately nine times greater in the north basin (seasonal average: 97 µg l^?1) than in the south basin (seasonal average: 12 µg l^?1). Total inorganic carbon was low (usually <0·8 mg l^?1), silica was sufficient for algal growth, and particulate organic carbon was 4·5 times higher in the north basin (average: 0·9 mg l^?1) than in the south basin (average: 0·2 mg l^?1). North‐basin streams showed strong seasonality in turbidity, particulate‐nitrogen and ‐phosphorus, and particulate organic carbon, whereas strong seasonality in south‐basin streams was observed in conductivity and dissolved nitrogen. Lake position influenced the seasonal dynamics in stream temperatures and nutrients, particularly in the groundwater/precipitation‐fed north‐basin network. Copyright © 2007 John Wiley & Sons, Ltd.