植被恢复和气候变化对汾河源区径流及其组分的影响

近年来,黄河中游许多流域径流量呈现减少的趋势,这与区域大规模的植被恢复密切相关。但是,汾河源区径流量却呈现了增加的相反趋势,有关变化环境对该区域径流及其组分的影响机制尚不明晰。因此,研究选取汾河源区北石河流域为研究区域,利用9种数值模拟法对1962-2018年河川径流进行分割并分析其适用性,采用Mann-Kendall检验法和累积距平法对径流、地表径流及基流进行了趋势分析和突变检验,评价了植被恢复和气候变化对径流及其组分的影响。结果表明:(1)在9种数值模拟法中,Lyne-Hollick滤波法的估算精度相对较高,其日基流过程线能较好地反映基流的滞后性和稳定性,因此更适用于研究区的基流估算;(2)流域多年平均径流深、地表径流深、基流深和基流指数分别为181.2 mm、67.4 mm、113.8 mm和0.68,基流是径流的主要组成部分。流域年径流和年地表径流均呈现不显著的增加趋势,而年基流呈现显著的增加趋势,基流的增加是径流变化的主要直接原因,三者的突变时间均出现在1994年左右;(3)降水的变化引起了径流、地表径流及基流的增加,降水增加是径流变化的主导因素(贡献率为78.1%-79.4%),而植被恢复引起了径流和基流的增加以及地表径流的减少,其主要原因在于植被恢复能够促进降水入渗,减少地表径流,同时北石河流域的土壤和地貌条件使增加的降水入渗量更多地形成了基流,植被恢复的基流增加效应超过了地表径流减少效应,从而最终增加了径流总量。研究结果可为汾河源区植被合理恢复及水资源可持续利用提供科学依据。

Impacts of vegetation restoration and climate change on runoff and its components in the source area of the Fenhe

In recent decades, large-scale vegetation restoration has been carried out in the middle reaches of the Yellow River, which is a significant factor leading to the reduction of runoff in many watersheds. Since 1988, the source area of the Fenhe has continuously carried out three phases of comprehensive soil and water conservation management, and the forest vegetation coverage in this area has significantly increased. However, the runoff in the Fenhe source area has shown an opposite increasing trend. The impact mechanism of changing environment on runoff and its components in the area is not yet clear. Beishihe is an important tributary of the Fenhe source area, and the runoff change in this watershed is mainly caused by the impacts of vegetation restoration and climate change. Therefore, this study selected the Beishihe watershed as the study area, and used 9 numerical simulation methods to separate the baseflow from 1962 to 2018. The trend of runoff, surface runoff and baseflow and their mutation years were analyzed using the Mann Kendall test and cumulative anomaly method. The impacts of vegetation restoration and climate change on runoff and its components were evaluated by the double cumulative curve method, regression analysis method, and elastic coefficient method. Results show that: (1) among the nine numerical simulation methods, the Lyne-Hollick filtering method had relatively higher estimation accuracy, and its daily baseflow process line could better reflect the hysteresis and stability of the baseflow. Thus, it was more suitable for baseflow estimation in the study area. (2) The average annual runoff depth, surface runoff depth, baseflow depth, and baseflow index of the watershed were 181.2 mm, 67.4 mm, 113.8 mm, and 0.68, respectively, which indicated the baseflow was the main component of runoff. The annual runoff and annual surface runoff showed an insignificantly increasing trend, while the annual baseflow showed a significantly increasing trend. The increase of baseflow was the main direct cause of runoff change. In addition, the results of mutation test showed that the abrupt changes in annual runoff and its components all occurred around 1994. (3) The precipitation change led to an increase in runoff, surface runoff, and baseflow, which played a key role on runoff change (the contribution rate was 78.1%-79.4%). Vegetation restoration led to an increase in runoff and baseflow, as well as a decrease in surface runoff. The main reason is that vegetation restoration could promote precipitation infiltration, thereby reducing surface runoff. At the same time, the soil and landform conditions of the Beishihe watershed made the increased precipitation infiltration more likely to form baseflow. The increase in baseflow caused by vegetation restoration exceeded the decrease in surface runoff caused by vegetation restoration, ultimately increasing the total amount of runoff. The study can provide scientific basis for the reasonable restoration of vegetation and sustainable utilization of water resources in the source area of the Fenhe.