Impacts of Vegetation Restoration on Hillslope Hydrological Processes Under Climate Change in the Taihang Mountains, China

The Taihang Mountains serve as an ecological barrier and headwater, playing a critical role in maintaining ecological balance and water security for the North China Plain. In recent decades, this region has experienced significant vegetation greening, accompanied by a decline in water resources. Hillslopes are the fundamental units for understanding how vegetation restoration influences local hydrological processes. However, the hydrological impacts of vegetation restoration at the hillslope scale remain poorly quantified. Based on observational experiments and the Brook90 eco-hydrological model, we simulated hillslope hydrological processes from 1991 to 2023, quantifying the effects of vegetation restoration on eco-hydrological processes in mountainous areas. The results indicated that (1) from 1991 to 2023, the average evapotranspiration, transpiration, and interception loss at the observation site were 441.1, 321.6, and 58.3 mm, respectively. Evapotranspiration, transpiration, and interception loss showed increasing trends, with cumulative increases of 112.0, 107.7, and 17.5 mm, respectively, while soil evaporation decreased by a cumulative total of −12.3 mm. (2) Vegetation restoration contributed to the increasing trends in evapotranspiration, transpiration, and interception loss, with cumulative contributions of 16.5, 36.4, and 21.9 mm, respectively. (3) Vegetation restoration increased evapotranspiration, driven mainly by transpiration and interception loss, while reducing soil water storage and runoff, highlighting its significant impact on water availability. Long-term quantitative observations of hillslope hydrological processes help to understand the decline in water yield due to vegetation recovery in mountainous areas. These findings offer crucial guidance for improving water conservation strategies and selecting afforestation species.