对西江枯季水量调度下径流演变特征及极端枯水特征进行分析,为西江流域枯季水量统一调度和水资源高效利用提供参考。选取梧州水文站1950—2015年逐日流量资料,采用Mann-Kendall法、滑动T检验、R/S法等多种方法对西江下游枯季水量调度前后枯水年月流量序列进行趋势性对比分析,并详细探讨其变异性及未来变化特征。结果表明:西江下游枯季流量呈不显著上升趋势,呈正持续性,且变异可能性较小;水量调度后枯季11月份,次年1月份和2月份流量呈显著上升趋势,而10月份流量明显下降,即呈现拦蓄汛末洪水补给枯水月份特点,但作为枯水关键期的12月份流量呈微弱上升趋势值得关注;枯季各月流量的Hurst指数和相关系数C(t)表明,未来西江下游枯季各月流量仍与过去趋势相一致,且无显著变异。PPCC检验表明,LP-Ⅲ型分布描述西江枯水年月流量频率分布最优,以该分布频率P=90%为极端枯水标准,显示枯季径流前期随着指标流量尺度变小,极端枯水发生变多,但后期变少,可见枯季水量调度一定程度上有助于减少极端枯水事件的发生。

By studying the characteristic of dry season runoff and extreme low-flow in the downstream of Xijiang River in the presence of water quantity dispatching, we aim to provide a reference for the unified scheduling in dry season and the efficient use of water resources in the Xijiang River Basin. According to the daily flow data at Wuzhou Hydrological Station from 1950 to 2015, we compared the annual and monthly low flow series before and after the water quantity dispatching via Mann-Kendall method, sliding T-test method, and R/S method, and discussed the variability and future change of low flow. Results revealed that over the past six decades, the dry season flow in the lower reach of Xijiang River showed no significant upward trend with a positive persistence and small possibility of variation. After water quantity dispatching, monthly low flow witnessed a significant upward trend in November, January and February, but decreased distinctly in October, presenting the characteristics of impoundment at the end of flood season. In December, a critical low-flow period, there was a slight upward trend, which is particularly worthy of attention. The Hurst index and correlation coefficient C(t) of each month’s flow indicate that the future monthly flow during dry season in the lower reach of Xijiang River will be consistent with the past trend with no significant variation. Probability plot correlation coefficient (PPCC) test demonstrates that the LP-III frequency distribution best fits the annual and monthly flow during dry season in Xijiang River Basin. Taking P=90% in this distribution frequency as extreme low-flow standard, we found that extreme low-flow occurred more with the reduction of index flow scale in the early stage, but less in the later stage, implying that water quantity dispatching in dry season is conducive to reducing the occurrence of extreme low flow events.