大凌河流域凌海站年径流量时间序列特征的小波分析

本文基于小波理论,采用Morlet小波分析了大凌河流域下游控制站—凌海站1961―2013年径流量时间序列变化特征。分析显示,凌海站多年径流量时间序列在53年分析时域内具有不均匀的时间尺度分布特征,且局部化明显;多年径流量序列变化主要受5―7a、14―16a和24―28a时间尺度的控制,具有6a、15a和27a左右的主周期。     

ENSO对珠江三角洲洪水影响

根据珠江三角洲1951—2008年34个潮位站年极高水位资料和Nino 3.4区海洋尼诺指数资料,采用GEV分布进行洪水频率计算,分析不同重现期洪水位的变化情况,对比分析洪水位重现水平在1980年前后空间变化特征。采用滑动相关分析,探讨珠江三角洲近50年来洪水位对ENSO(El Nino/La Nisa-Southern Oscillation)响应的年际变化特征。结果表明,珠江三角洲整个区域的洪水频率分布自下游到上游逐渐增大,沿海比中上游地区更易受洪涝灾害威胁。绝大多数站点不同重现期洪水位变化趋势一致,部分站点水位变化方向不完全一致。洪水位有减小趋势的站点分布在三角洲上游地区,中下游地区则主要呈现为增长趋势。洪水位与ENSO之间年际变化关系有明显阶段性,在1980年发生明显改变,跃变前后滑动相关系数的符号或强度有明显差异。洪水位对不同季节的ENSO响应不同,不同时期ENSO对洪水位的影响不同。     

长兴区域降水变化及趋势分析

利用长兴地区共9个雨量观测测站,1976—2011年的月平均降水量资料,运用趋势分析和EMD方法,根据长兴地区相应的地理特征,将该地区划分为平原和山区两区域,分别对两区域37 a来降水量变化的基本特征进行比较和分析,结果表明:①平原和山区年降水量距平百分率都呈略为下降趋势,山区下降趋势较平原更明显;②春季、夏季、秋季和冬季两地区的降水距平百分率的变化与年变化一致;③1990年代后期,平原地区降水距平百分率趋势的变幅明显大于山区,山区年代际降水量正距平出现的时间滞后于平原地区;④降水量变化方面,长兴地区呈现单调下降趋势,具有四类尺度的变化周期,分别是2～3 a,5 a左右,7～8 a及20 a左右。     

不同时间尺度的径流时间序列混沌特性分析

径流序列的动力行为是在复杂非线性和多尺度现象综合作用下的外在表现.基于混沌理论和相空间重构理论,以金沙江和美国Umpqua河统计的日径流序列为研究对象,对不同时间尺度(日、旬和月)的径流序列,首先利用0-1混沌测试算法计算其渐进增长率,探讨径流序列混沌特性随时间尺度的变化规律,然后重构以上径流序列的相空间,分别计算关联维数、最大Lyapunov指数和Kolmogorov熵.用这3个混沌判别指标分析不同时间尺度下径流序列的混沌特性及其随时间尺度的变化规律.研究结果表明,时间尺度和径流序列非线性特征之间的关系并不明显,渐进增长率随时间尺度的增加并无明显的变化规律,嵌入维数则随时间尺度的增大呈减小趋势,最大lyapunov指数和Kolmogorov熵随着时间尺度的增加逐渐增大.     

Scaling of sediment dynamics in a laboratory model of a sand-bed stream

A movable bed model was designed in a laboratory flume to simulate a mixed load sand-bed stream. The modelling objectives were to reproduce bedload and suspended sediment transport as well as downstream and transverse sediment fluxes in ratios similar to the field site. To meet these objectives the model contained an exact geometric scale and graded lightweight sediments to simulate migrating dunes and suspended load transport. The experiments are somewhat novel in that most mobile bed models have vertical exaggeration, whereas in these experiments exact geometric similitude of channel dimensions was maintained. The goal of this paper is to review the scaling strategy and the level of similarity among dimensionless parameters between model and field. Similarity in dimensionless bed shear stress and the particle Reynolds number enabled the experiments to replicate the dominant sediment dynamics present in the stream during a bankfull flow. There was a conflict in the strategy, in that grain roughness was exaggerated with respect to nature. However, the paper shows that geometric similarity of bedforms and the resulting drag is much closer to what is predicted for nature. In addition, measurements of sediment transport are compared to values computed from well-supported formulations, which is shown to reinforce the validity of the scaling strategy. Lastly, criteria for movable bed equilibrium are defined and it is shown that lightweight sediments contributed to the rapid development of near-equilibrium conditions. Overall, the paper shows a methodology that can be used to model mixed load streams at an exact geometric scale.     

Characteristics of the interannual and interdecadal timescales of evaporation in Northern China in the recent 115 years

1. INTRODUCTION To calculate long-term average, total evaporation is considered to be equal to precipitation and has key effects on the global water balance [1]. In recent years, several studies on climatic changes with respect toevaporation were carried …