Vegetation Dynamics Regulate Baseflow Seasonal Characteristics in the Chaohe Watershed of Northern China

The implementation of ecological restoration programs (ERP) and the acceleration of climate change (CC) in recent decades have led to severe water shortages and threatened water security and ecosystem function in Northern China. Baseflow is essential for sustaining river flows, yet its seasonal responses to CC and ERP remain not fully understood, which limits the understanding of available water resource variation and the mechanisms behind them. In this study, we quantified and attributed the variation in baseflow across dry and wet seasons in the main source of Beijing's potable water – the Chaohe watershed of Northern China from 1961 to 2016 by thoroughly assessing nine different approaches for separating baseflow. We found that the two-parameter Eckhardt digital filter method could better characterize baseflow variation. Hereinto, the wet-season dominated baseflow (seasonality ratio was 2.12 ± 1.28 on average) accounted for 64.21% ± 13.04% about the entire year in the watershed. Both dry and wet seasons' baseflow exhibited a significant reduction, with changes of 32.61% and 68.21%, therefore posing more serious threats to the sustainability of water resources, especially under the prevailing global warming. For the baseflow variation, we further found the significantly declined sub-surface runoff (with a rate of 1.91 mm per decade) played a critical role in the decrease in dry-season baseflow. Meanwhile, vegetation regulated the seasonal distribution of water resources and maintained dry-season streamflow. It is vital to improve water resource management by vegetation measures, especially in water-limited regions. However, as a supplementary water source, the decrease in wet-season baseflow was the result of offering more water supply to meet the evapotranspiration demand. Overall, our findings offer novel insight into understanding the influence of vegetation dynamics on water resources and highlight the essential role of vegetation in regulating baseflow to maintain water balance and water resources' seasonal distribution.