Coupling of dynamic hydrological response units and SWAT-MODFLOW to model the impact of vegetation change on hydrological processes in an arid endorheic river watershed

Abstract Vegetation change in arid areas may lead to the redistribution of regional water resources, which can intensify the competition between ecosystems and humans for water resources. Thus, it is necessary to understand the impact of vegetation change on hydrological processes in arid areas. We aimed to accurately model the impact of vegetation change on hydrological processes in an arid endorheic river watershed undergoing revegetation. The middle and lower reaches of the Bayin River basin, China were investigated because this is an area of frequent surface water–groundwater interactions and evident revegetation. A LU-SWAT-MODFLOW model was developed by integrating dynamic hydrological response units with a coupled SWAT-MODFLOW model, which can reflect actual land cover changes in the basin. The results showed that the LU-SWAT-MODFLOW model outperformed the original SWAT-MODFLOW model in simulating human activity impact as well as the leaf area index, evapotranspiration, and groundwater table depth. After regional revegetation, evapotranspiration in different sub-basins increased by 1.5 mm per month and by 6 mm per year. The groundwater recharge increased by 1.27 mm on average per month and 14.02 mm on average per year. Irrigation for the recovered vegetation strongly affected the groundwater recharge. In addition, the direction and amount of surface water–groundwater exchange considerably changed in areas where revegetation involved converting low-coverage grassland and bare land to forestland. In areas where revegetation involved converting farmland to forestland, the transition had a weak effect on the direction and amount of surface water–groundwater exchange.