南岭山地森林流域退水规律及影响因素

采用水文气象长期定位观测数据，结合基于事件尺度的退水速率与流量关系分析方法，对2019—2021年典型南岭山地森林流域的退水过程变化进行识别，探索退水特征与同期土壤水分、地下水埋深、潜在蒸散发和实际蒸散发的关联程度，深入了解山地森林流域退水规律及主要影响因素。结果表明：1）相同流量情况下，流域在枯水条件下比丰水条件退水速率更快；2）流域土壤入渗能力较强，降水能迅速补给土壤水和地下水，地下水对降水的响应较土壤水略有延迟；3）地下水埋深对流域退水有显著影响，土壤水分次之，与之相比潜在蒸散发和实际蒸散发的影响并不明显；4）地下水埋深是影响山地森林流域出口退水过程的最主要因素，由于地下水位低于河床位置，流域出口河段处于地下水补给区，因此地下水埋深越深，河道水向地下水渗失越快，从而导致流域出口退水速率加快。可见，地下水埋深是流域退水规律分析乃至枯水期径流模拟不可忽略的关键变量。

Streamflow Recession and Dominant Factors in the Nanling Mountain Forest Catchment

Little attention has been paid to dry season streamflow and groundwater recharge dynamics compared to the systematic focus on measuring total annual streamflow changes associated with forest. However, in the tropics and subtropics, especially in regions with uneven seasonal distribution of precipitation, dry season streamflow and groundwater recharge are of great importance for the riverine ecosystem stability and downstream water supply safety. Recession analysis of -dQ/dt~Q is widely used for determining the catchment storage-discharge relationship and predicting dry season streamflow processes. When dQ/dt~Q plots of streamflow recession are constructed for individual events, the slopes of the curves are near constant in log space, but the intercepts vary with time. Previous studies used event-based analysis to hypothesize that the shifts in intercept in dQ/dt~Q curves were due to variations in concurrent evapotranspiration (ET), which is consistent with the dominant belief regarding controls on streamflow recession. On the contrary, increasing evidence suggests the possibility that other factors such as soil moisture, groundwater recharge, or active drainage network may play a role in dQ/dt variations. However, no consensus has been reached on the determinants of the shift. By using an event-based recession analysis, an experimental catchment with long-term hydrometeorological observations was selected to investigate the streamflow recession in the Nanling mountain forest. Our results showed that 1) faster recession rates were more likely to occur under dry conditions than those under wet conditions; 2) groundwater depth varied consistently with soil moisture in response to precipitation, indicating high soil infiltrability; 3) a significant correlation between the intercept a and concurrent groundwater depth demonstrated its potential role as explanatory variable of streamflow recession; 4) as a losing stream (groundwater depth always larger than 5.0 m near the catchment outlet), water loss to groundwater recharge appears to be the dominant factor affecting streamflow recession.