Understanding Hydrological Process Change due to Re-Vegetation in a Mountainous Watershed of Northern China

Hydrological processes of mountainous watersheds commonly impact water resource supply in downstream areas. To better understand how re-vegetation affects the different hydrological pathways of watersheds, we investigated their change at various temporal scales for the Xiaoluan River watershed, a typical meso-scale watershed featuring a plateau–mountain transition topography in northern China. For the non-growing season from 2006 to 2020, the groundwater discharge of the watershed and the wetting of the watershed in terms of the Horton Index significantly increased, and the recession process in terms of the recession coefficient (k) was considerably prolonged. We suggest that re-vegetation and snowmelt were responsible for this change, but they affected the hydrological processes differently. That is, re-vegetation might improve the water storage capacity of the shallow soil layers of the watershed, thereby enhancing the capacity of groundwater recharge and discharge. Meanwhile, snowmelt may provide available water for recharging and discharging the watershed. Because reforestation progresses and global climate change continues, more complex hydrological processes are to be expected. Therefore, continuous monitoring and detailed investigations of subsurface hydrological processes will be necessary for adaptive watershed management.