祁连山疏勒河上游基流变化及其影响因素分析

基流是河川径流的重要组成部分，也是干旱半干旱地区最重要的枯季水文特征之一. 基流在维持河川径流和维护河流湖泊生态等方面具有重要意义. 基于祁连山疏勒河上游出山口控制水文站昌马堡站1954-2009年的日径流资料，采用递归数字滤波法和平滑最小值法对日径流进行基流分割，对比分析基流和基流指数BFI的变化特征，并从气温和降水两方面探讨基流变化的主要影响因素. 结果表明：两种方法的计算结果有差异，但平滑最小值法更适用于研究区. 疏勒河上游多年平均基流量为6.07×10⁸m³，基流变化总体上呈上升趋势，进入21世纪以后基流量增加最为显著. 研究区多年平均基流指数为0.66，基流指数的年际变化相对比较稳定，但年内波动幅度较大. 在长时间尺度上，降水是基流变化的主要影响因素，降水量的增加在一定程度上影响了基流和基流指数的变化. 在全球变暖的背景下，气温升高导致冰雪融水的增加和冻土的退化，间接的影响了基流的变化.

Variation of the base flow and its causes in the upper reaches of the Shule River in the Qilian Mountains

As an important component of runoff, base flow is one of the most important hydrological characteristics in dry season in arid and semi-arid regions. Base flow has significant in maintaining runoff and preserving ecological environment of rivers and lakes. Based on daily runoff data from 1954 to 2009 in the upper reaches of the Shule River, the recursive digital filter and smoothed minimum method were used for base flow separation. The features of variation in base flow and base flow index, as well as the main controlling factors (temperature and precipitation), were investigated. It is found that there is a difference between the calculation results from the two methods, but the smoothed minimum method is more suitable for the study area. The average annual base flow is 6.07×10⁸ m³. As a whole, the base flow is increasing in the upper reaches of the river, similar to runoff, especially in the period of early 21st century. The base flow index is 0.66 in the study area, which is relatively stable, but whose fluctuating range is great throughout the year. In a long term, precipitation is a major influence factor to the change in base flow and base flow index. Under the background of global warming, rising temperature leads to increase snow melt and permafrost degradation, which will be increasing the supply to base flow.