Impact of increasing vegetation coverage on gaining and losing streams in an arid endorheic river watershed

To improve the ecology in northern China, the Chinese government has launched a series of revegetation projects. However, the impact of increasing vegetation coverage on gaining and losing streams remains largely unexplored, particularly in arid endorheic watersheds with frequent exchanges of water and other materials between surface water and groundwater. To address this, we modified the vegetation growth module of the soil and water assessment tool (SWAT) to simulate the vegetation coverage change proposed for the middle and lower reaches of the Bayin River. We then coupled the modified SWAT to a modular finite-difference groundwater flow model to simulate the surface and subsurface water exchange. Hydrological, meteorological, and hydrogeological observation data were then used to build and calibrate the coupled model for the period 2001-2019. We set two vegetation coverage scenarios (non-revegetation and vegetation) and two irrigation variants (non-irrigation and irrigation) to investigate the impact of changes in vegetation coverage and the related irrigation variant on gaining and losing streams. The results showed that the vegetated land area and annual leaf area index both increased significantly between 2019 and 2001. The groundwater discharge to the gaining streams was more strongly affected by revegetation and related irrigation than the groundwater recharge from the losing streams. Irrigation related to revegetation emphasizes the effect of revegetation on streamflow. We suggest that in arid endorheic river basins, because of the related irrigation, revegetation has a substantial impact on groundwater level and streamflow, which is mainly composed of baseflow. Therefore, the irrigation efficiency of newly planted vegetation must be improved to stabilize the groundwater level and related ecological conditions. Groundwater discharge into the gaining streams was more affected by revegetation and related irrigation than groundwater recharge from the losing streams. Revegetation-related irrigation made the effect of revegetation on streamflow more pronounced.image