夏秋季长江、黄河流量长期变化的主要特征

利用20世纪后50 a或更长时间的水文资料,研究长江、黄河夏秋季流量长期演变的主要特征。统计分析得出:长江、黄河夏秋季流量都占年总量的一半以上,月均流量和标准差均为其他月份的2.6倍或更大。长江夏秋季流量的标准差约为其多年平均流量的22.1％,黄河则为58.8％。长江夏秋季的平均流量约为黄河的15.7倍,相应标准差为5.9倍。二者相比,长江流量大而稳定,黄河流量比长江小1个量级,而相对变化幅度大一倍以上。黄河流量自20世纪30年代中期至1968年正距平为主,累积距平曲线持续上;而自1985年至今负距平占绝对优势,流量逐年下降,下游频频断流。利用Petitt计算变点的方法可以找出长江、黄河流量以往主要的显著变点。利用快速富利叶计算法,对黄河流量进行谐波分析,得出黄河流量在未来几年内将逐渐增加。

MAIN FEATURES OF LONG-TERM VARIABILITY OF STREAMFLOW IN THE CHANGJIANG AND HUANGHE RIVERS IN SUMMER-AUTUMN SEASONS

The main features of long-term variability for the two largest rivers of Changjiang and Huanghe in summer-autumn seasons were studied based on observations of streamflow for the last 50 or more years. It is shown that the steamflow in two rivers in summer-autumn seasons occupies more than a half of the annual streamflow; the monthly mean streamflow and standard deviation in the summer-autumn seasons are 2.6 times of or more than that in other months; the average steamflow in Changjiang River is 15. 7 times, and the standard deviation is 5.9 times of that in Huanghe River for the summer-autumn seasons. The standard deviation of streamflow in Huanghe River is about 58.8% of the long-term average streamflow, but only about 22.1% in Changjiang. In comparison, the steamflow of Changjiang River is larger and more stable than Huanghe River. The Huanghe steamflow is one order less than, and unstable two times than that in Changjiang River. The streamflow anomalies in Huanghe River were mainly positive during the period from middle of 1930s to 1968; but turned to mostly negative since 1985. The lower reaches of the Huanghe River dried up with zero-steamflow frequently. The marked change points are found based on the calculation of change point proposed by Petitt. A harmonic analysis and a prediction of the streamflow for Huanghe River was carried out based on the dominant Fourier waves. The predictions suggest that the Huanghe steamflow will trend toward increase before 2005.