On the distribution of flood volume in partial duration series analysis of flood phenomena

A methodology based on the theory of stochastic processes is applied to the analysis of floods. The approach will be based on some results of the theory of extreme values over a threshold. In this paper, we focus on the estimation of the distribution of the flood volume in partial duration series analysis of flood phenomena, by using a bivariate exponential distribution of discharge exceedances and durations over a base level.     

Evaluation of risk concepts in partial duration series

Conventional design practice aims at obtaining optimal estimates of floods with specified exceedance probabilities. Such estimates are, however, known on the average to be exceeded more frequently than expected. Alternatively, methods focusing on the expected exceedance probability can be used. Two different methods are considered here; the first is based on the sample distribution of true exceedance probabilities. The second is a Bayesian analogue using the likelihood function and a noninformative prior to describe the variability of exceedance probabilities. Appropriate analytical solutions are presented in both cases using the partial duration series approach.     

Rainfall estimation using raingages and radar — A Bayesian approach: 1. Derivation of estimators

Procedures for estimating rainfall from radar and raingage observations are constructed in a Bayesian framework. Given that the number of raingage measurements is typically very small, mean and variance of gage rainfall are treated as uncertain parameters. Under the assumption that log gage rainfall and log radar rainfall are jointly multivariate normal, the estimation problem is equivalent to lognormal co-kriging with uncertain mean and variance of the gage rainfall field.The posterior distribution is obtained under the assumption that the prior for the mean and inverse of the variance of log gage rainfall is normal-gamma 2. Estimate and estimation variance do not have closed-form expressions, but can be easily evaluated by numerically integrating two single integrals. To reduce computational burden associated with evaluating sufficient statistics for the likelihood function, an approximate form of parameter updating is given. Also, as a further approximation, the parameters are updated using raingage measurements only, yielding closed-form expressions for estimate and estimation variance in the Gaussian domain.With a reduction in the number of radar rainfall data in constructing covariance matrices, computational requirements for the estimation procedures are not significantly greater than those for simple co-kriging. Given their generality, the estimation procedures constructed in this work are considered to be applicable in various estimation problems involving an undersampled main variable and a densely sampled auxiliary variable.     

淮河上游大暴雨的水分平衡

分析了淮河上游大暴雨过程的水汽来源和暴雨区的水分平衡。结果说明，暴雨区除有大量水汽净通量外，还有相当数量的水分来自云的净输送，尤其是大暴雨中心附近，积雨云团的净通量决定降水量的大小。因此，分析云的移动和变化是暴雨预报的重要课题。     

1991年北半球夏季风及江淮流域降雨量的低频振荡

根据１９９１年５－８月江淮特大暴雨资料，使用功率谱和带通滤波结合的方法，研究了１９９１年夏季风和江淮梅雨的准周期振荡，探索季风对异常梅雨的影响。分析指出，１９９１年北半球夏季风活动，江淮流域湿度场和降雨量变化均存在显著的准２４天周期振荡，夏季风的周期振荡，主要表现在西南季风（东南季风不明显），它的位相比降雨量提前２－４左右，其振幅大小较好地反映了降雨量的大小。     

东亚梅雨锋暴雨研究进展

对梅雨锋的大尺度环流、梅雨锋的次天气尺度和中尺度特征、梅雨锋低空急流和暴雨发展等问题的研究进展作了概述，对低空急流和暴雨发展的各种观点进行了评述，并提出了新的见解和研究结果。     

暴雨类冷涡与非暴雨类冷涡的合成对比分析

选择了８例典型的东北冷涡暴雨过程和８例典型的东北冷涡弱降水过程进行了合成对比分析，发现暴雨类冷涡其暴雨主要出现在冷涡的发展阶段，而非暴雨类冷涡的降水主要发生在冷涡的成熟阶段；暴雨类冷涡与其南侧的副热带低值系统联系密切，非暴雨类冷涡的这一特点不甚明显；暴雨类冷涡的两个降水中心分别出现在系统东侧偏南和南侧偏东一些的地，距系统中心大约３００－４００ｋｍ和７００－８００ｋｍ，这些区域处于低层辐合、高层辐菜     

数字卫星云图估算面雨量的应用试验

使用云分类降水率估计的方法，有静止气象卫星数字云图进行面雨量估算。对１９９３年８月４日华北南部一次降水过程的实测雨量与估算结果的对比分析表明，这种估算方法对雨区的差别有相当高的精度，对雨量的估计有一定的参考价值。     

我国5月降水的气候特点和长期变化

从月尺度降水长期预报业务的需要出发，根据中央气象台长期科１６０站月降水资料，分析了中国５月份降水的基本气候特点和长期变化，进一步明确了５月份降水预报业务的工作重点，揭示出某些对５月份降水预报业务有价值的气候现象，其中５月份南北方降水长期变化的阶段性及其反位相振荡现象（ＳＮ现象）对５月份降水长期预报业务具有重要实践意义。     

Temporal and spatial rainfall analysis across a humid tropical catchment

Temporal and spatial rainfall patterns were analysed to describe the distribution of daily rainfall across a medium‐sized (379km²) tropical catchment. Investigations were carried out to assess whether a climatological variogram model was appropriate for mapping rainfall taking into consideration the changing rainfall characteristics through the wet season. Exploratory, frequency and moving average analyses of 30 years' daily precipitation data were used to describe the reliability and structure of the rainfall regime. Four phases in the wet season were distinguished, with the peak period (mid‐August to mid‐September) representing the wettest period. A low‐cost rain gauge network of 36 plastic gauges with overflow reservoirs was installed and monitored to obtain spatially distributed rainfall data. Geostatistical techniques were used to develop global and wet season phase climatological variograms. The unscaled climatological variograms were cross‐validated and compared using a range of rainfall events. Ordinary Kriging was used as the interpolation method. The global climatological variogram performed better, and was used to optimize the number and location of rain gauges in the network. The research showed that although distinct wet season phases could be established based on the temporal analysis of daily rainfall characteristics, the interpolation of daily rainfall across a medium‐sized catchment based on spatial analysis was better served by using the global rather than the wet season phase climatological variogram model. Copyright © 2001 John Wiley & Sons, Ltd.