砚瓦川流域河川基流变化规律及其驱动因素

基流是黄河径流的重要补给来源，目前大部分研究都集中在黄河流域径流变化规律上，而对维持河道基本流量和生态环境安全方面发挥着重要作用的基流却研究较少。因此，基于黄河中游砚瓦川流域1981-2016年的水文、气象及植被资料，选用9种数值模拟法对基流进行分割并分析其适用性，利用Mann-Kendall法和滑动t检验法对基流进行了趋势分析和突变点检验，并定性和定量的探讨了气候变化和植被变化对流域河川基流变化的影响。结果表明：（1）在各种基流分割方法中，Lyne-Hollick滤波法的计算结果精度较高，且分割结果比较符合实际日基流变化规律，因此更适用于研究区的基流估算；（2）流域多年平均河川基流量和基流指数BFI （基流量与河川流量的比值）分别为0.152 m³/s和0.58，两者在年际上均呈现极显著的减少趋势（P<0.01），且分别于1993年和2006年附近发生了突变；（3）基流量与潜在蒸散发量相关性最强，流域降水量、潜在蒸散发量及NDVI的变化对基流量变化的贡献率分别为-99.1%、113.3%和85.8%，可见潜在蒸散发量和NDVI的增加是引起基流量减少的主要原因，而基流指数与NDVI相关性最强，且呈负相关关系，流域降水量、潜在蒸散发量及NDVI的变化对基流指数变化的贡献率分别为41.3%、-27.7%和86.5%，这说明流域NDVI的增加对流域基流指数的降低起到了主导作用。

Study on the variation of baseflow and its driving factors in the Yanwachuan watershed

Baseflow plays an important role in sustaining streamflow in the Yellow River watershed. Most of the recent researches have focused on the runoff variations in the Yellow River watershed, however, only a few studies investigated the variations of baseflow which are important to maintain the basic flow and ecological environment security. In this study, the Yanwachuan watershed was selected as the study area in the middle reaches of the Yellow River. Based on the hydrological, meteorological and NDVI (Normalized Difference Vegetation Index) data from 1981 to 2016 in the Yanwachuan watershed, nine numerical simulation methods were selected to separate the baseflow and were compared to analyze their applicability in the study area. The Mann-Kendall trend test and sliding t-test were then used to identify the changing trends and mutation points of the baseflow. Furthermore, the impacts of climate change and vegetation change on the baseflow were also qualitatively and quantitatively discussed. The results of this study can be drawn as follows:(1) Lyne-Hollick filtering method had higher accuracy than other separating methods, and its separating results were very consistent with the actual variations of daily baseflow. Thus, it was indicated that the Lyne-Hollick filtering method was more suitable for the baseflow estimation in the Yanwachuan watershed. (2) The average annual baseflow and baseflow index (the ratio of baseflow to runoff) of the Yanwachuan watershed were 0.152 m³/s and 0.58, respectively. According to the results of the M-K statistical test and sliding t-test, the annual baseflow and baseflow index were both significantly declined from 1981 to 2016 and their mutation points occurred in 1993 and 2006, respectively. (3) The correlation between baseflow and potential evapotranspiration was the strongest, while the correlation between baseflow index and the NDVI was the strongest and negative. The contribution rates of precipitation variation, potential evapotranspiration variation, and NDVI change to the decrease of baseflow were -99.1%, 113.3% and 85.8%, respectively, while the corresponding contribution rates to the reduction of baseflow index were 41.3%, -27.7% and 86.5%, respectively. It was clear that potential evapotranspiration variation and NDVI change were the main factors causing the decrease of baseflow, while the influence of NDVI change played a key role on baseflow index reduction.