Assessing the impacts of irrigation and soil types on the water balance and groundwater depletion in an irrigation district of the North China Plain based on a coupled SWAT-MODFLOW model

Well irrigation can alter water balance and threaten the sustainability of groundwater resources globally. It is a challenge to quantitatively evaluate the effect of complex irrigation water use in different soils on the water balance in the vadose zone and in the phreatic aquifer at a regional scale. An irrigation district in the North China Plain was chosen as the study site, where the soil types were mainly sandy loam and silt loam in well-irrigated areas and silt in surface water irrigation areas. The coupled SWAT-MODFLOW model was robustly verified by the two-year monthly soil water content and groundwater level data. Evaluation of water balance components across the entire study area showed that under the precipitation of 426 mm yr −1 and irrigation of 300 mm yr −1 (5.7 % surface water and 94.3 % groundwater), the actual evapotranspiration (actual ET) was 514 mm yr −1 , soil water recharge to groundwater was 252 mm yr −1 , and the groundwater amount declined 90 mm yr −1 . Irrigation increased the actual ET by 191 mm yr −1 and soil water percolation to groundwater by 134 mm yr −1 compared with the non-irrigation scenario. Groundwater abstraction for irrigation resulted in less soil water percolation (220 mm yr −1 ) and higher groundwater depletion (181 mm yr −1 ) in the sandy loam region than in the silt loam region where soil water percolation was 281 mm yr −1 and groundwater depletion was 161 mm yr −1 . The higher antecedent soil water content resulted in higher soil water percolation in fine-textured soil. Irrigation optimization measures are necessary to mitigate groundwater depletion in coarse-textured soil in the irrigated region of the North China Plain. • SWAT-MODFLOW was verified by two-year monthly soil water and groundwater level data. • Irrigation increased actual ET of 191 mm yr −1 and soil water percolation of 134 mm yr −1 . • Mixed water source irrigation caused groundwater amount declination of 90 mm yr −1 . • Sandy loam with low initial soil water content showed less soil water percolation than silt loam.