宜昌站1900~2004年生态水文特征变化

基于宜昌站1900~2004年共105年的日径流量资料，分别采用Mann Kendall法、Mann Whitney法分析该站水文特征与变化。跳跃性检验表明，宜昌站年平均流量的跳跃点出现在1969年，置信度超过99%。宜昌站1970年前的平均流量是14 375 m3/s，1970年后的平均流量是13 438 m3/s，相差937 m3/s，相当于295.5 m3/a，流量减少主要集中在下半年（7~12月），以8~10月最为明显。以1970年为界，将宜昌站105年水文序列划分为“近自然状态河流” 的1970年前和“人工干扰状态河流”的1970年后两个分析水文变动序列，基于Richter提出的生态水文变动指标体系，应用变动范围法，计算了长江中游的生态水文目标，分析了长江流域宜昌站的生态水文特征变化。结果表明，1970年以后，人类活动与自然变动对长江宜昌站生态水文特征的改变并不明显，仅在1月、11月平均流量上有中等程度的改变。

ASSESSMENT OF ECO-HYDROLOGICAL ALTERNATION (1900～2004) IN YICHANG GAUGE OF THE YANGTZE RIVER

The temporal variability of daily discharge from 1900 to 2004 in Yichang Gauge,which is located in the upper reaches of the Yangtze River with a catchment area over 1 million km~2,has been analyzed in the present study.The Mann-Kendall statistical test was applied to assess the significance of the trends.There is a decrease trend in annual and monthly discharge series,and the trend is significant at annual level and in February,August,October and November with the decrease significance exceeding 95% confidence.The Mann-Whitney statistical test was also applied to assess the jump of trends.A jump happened in 1969 with the confidence exceeding 99%,and the difference of mean discharge before 1970 and after 1970 is 937(m~3/s)(6.5%).The Range of Variability Approach(RVA),which contains thirty-two eco-hydrological parameters called Indicators of Hydrologic Alteration(IHA),was used to evaluate the flow conditions before and after 1970.25th to 75th percentile values for each parameter before 1970 was set at the management target range.It is shown that light hydrological alternations are observed for most parameters,except five parameters including monthly discharge and rate/frequency of water condition changes parameters in January and November.The hydrological alternation is mainly due to the decrease in precipitation and the construction of dams in the upper Yangtze Basin.