2006年长江特枯径流特征及其原因初探

PRELIMINARY ANALYSIS OF CHARACTERISTICS OF THE EXCEPTIONAL LOW DISCHARGE AND ITS CAUSE OVER THE YANGTZE RIVER,2006

2006年长江流域出现了百年罕见的特大枯水，对长江流域用水和生态环境都产生了深远影响。使用2006年长江干支流主要水文站水情资料和长江流域气象资料，并同时考虑了三峡蓄水的影响，分析了2006年长江径流过程特征及其原因。研究发现，2006年长江径流量减少主要是汛期径流量显著减少所致，表现出“汛期特枯”的特点。径流量和水位最大降幅都出现在8～9月份，各站径流量最大减幅都超过50％，水位汛期也有显著下降。洞庭湖、汉江与历史同期相比，汛期来水也明显偏小；而鄱阳湖来水略丰，对干流枯水起到一定的缓和作用。7、8月份长江上游区（特别是屏山至宜昌区间）降水少气温高是形成长江汛期特枯的主要原因。气象变化与径流变化存在较好的对应关系。三峡蓄水使2006年10月宜昌站径流量减少了一半左右，而对10～11月大通径流减少影响率为18．7％。

Exceptional low flow happened over the Yangtze River in 2006 and had some significant influ- ences on water usage and environment. By using the runoff data of main hydrological station and weather data,as well as taking the influence of TGP water storage into account, the runoff characteristics and its cause were studied. It is found that the decrease in discharge this year is mainly due to the significant loss of water in flood season and the discharge is characterized by exceptional low during that time. The maximum reduction of runoff and water level of hydrological stations occur during August and September. Maximum runoff reduction is all beyond 50 % and the water level has significant drop at the same time. Compared with that in the same time of history, the water-income from Dongting Lake and Hanjiang River is significantly less while the water from Poyang Lake is plentiful which to some extent lightens the severe low discharge in the main stream. The extreme low precipitation and high temperature over upper reaches （especially the area between Pingshan and Yichang） is the main cause of the exceptional low discharge. There is a good relationship between variation of weather and runoff. Water storage of Three Gorges Project decreases the October discharge of Yichang hydrological station by 50% and the influential index to the discharge decrease of Datong hydrological station from October to November is 18.7%.