Using upstream of Hengtangcun station in Xitiaoxi Basin as a study target, the characteristics, trend and influencing factors of annual runoff variation from 1972 to 2009 was analyzed with various numerical analysis methods,cumulative average deviation method and Mann-Kendall method based on long-term hydrological and meteorological observation data. The results indicated that the distribution of annual runoff was uneven, and the non-uniformity of distribution had weakened since 1980's. Compared to annual precipitation, annual runoff showed a bigger fluctuation,and the basin had been in a state of low flow or dried up since 2000. There was a significant decline in the annual runoff, while the decline trend in precipitation was not significant, and the correlation between precipitation and runoff was decreasing year after year. Precipitation was not the only factor influencing the runoff, and human activities such as hydraulic engineering, soil and water conservation, and water resources utilization were important factors for the large decrease of annual runoff.%以西苕溪横塘村站以上流域为研究对象,基于长期水文气象实测资料,运用多种数值分析方法、累积距平法以及Mann-Kendall非参数检验法,分析了1972-2009年西苕溪径流年内和年际变化特征、变化趋势及其影响因素.结果表明:西苕溪径流年内分配不均匀程度自20世纪80年代初逐渐减弱;相比年降水,径流的年际波动幅度普遍较大,2000年后流域基本处于枯水或偏枯状态;年径流量总体上呈显著的减少趋势,而年降水量减少趋势微弱,且两者相关性逐年代递减;西苕溪径流大幅度减少除降水驱动外,还与流域内水利工程、水土保持以及水资源利用等人类活动因素有关.
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