中国主要河流干旱特性的统计分析

STOCHASTIC ANALYSIS OF THE DROUGHT PROPERTIES OF THE MAIN RIVERS IN CHINA

在大量实测年径流量资料的基础上，分析了作为水文干旱定量指标负轮长的统计变化特性，并以哈尔滨和陕县站为例，以随机模拟途径探讨了严重干旱出现可能性的定量估计方法。结论是：Ｐ－Ⅲ型分布可用来表示负轮长的统计特性；平均负轮长和一阶自相关系数有密切的关系并具有一定的分区性；严重干旱出现可能性的定量估计，随机模拟途径最适当。

A drought is recognized as natural phenomenon which is characterized by the fact that demanded water quantity surpasses natural supply. However, on its definitions and quantitative indices there is no general agreement. In order to examine the drought properties of the main rivers in china, negative run lengths (NRL) is chosen as an index indicating the quantitative degree of a drought. In this paper NRL is defined by persistent duration of annual runoff related to negative deviation from mean annual runoff. The choice of NRL is due to its clear concept, convenient computation and ability in comparison. Based on a large number of observed data on the main rivers in China, the statistical properties of NRL such as distribution, mean value, and maximum value have been exmined in this paper. The distribution type of NRL is explored and identified by using a station year method. The final results obtained in this paper can be summarized as follows: 1. Pearson Type Ⅲ distribution may be used to describe the statistical properties of NRL on the main rivers in China; 2. Mean NRL has a close relation to first order autoregressive coefficient of annual runoff; 3. Maximum NRL within a period can be taken as a measure of drought severity. Its occurrence probability may be reasonably estimated by using a stochastic generation approach. Two case studies are given for two hydologic stations: Harbin and Shanxian.