Enhancing the capability of hydrological models to simulate the regional agro-hydrological processes in watersheds with shallow groundwater: Based on the SWAT framework

•Enhanced hydrological model (SWAT-AG) is proposed based on SWAT framework.•Close interactions of soil water, groundwater and plant growth are well described.•Hydrological processes in watershed with shallow aquifer are reasonably simulated.•SWAT-AG improves the model performance in agro-watershed compared with SWAT. This article introduces the SWAT-AG (a modified SWAT for agro-hydrological modeling) as an enhanced hydrological model for simulating the hydrological processes in agricultural watershed with shallow water tables. The model is developed based on the framework of the SWAT with significant improvements on describing the interactions of the vadose zone water, groundwater, salt and plant growth. The main features of the SWAT-AG include that it can simulate the close interactions of soil water and shallow groundwater with considering the capillary rise effects; it provides functions to simulate the soil salt movement and salt-stress on plant growth; and it incorporates a balance-based module on a sub-basin scale for shallow aquifer with involving canal seepage and ditch drainage calculation. Model testing and application were conducted in Jiyuan Irrigation System located in the Hetao of upper Yellow River basin, northwest China. The comparison between simulated and observed data showed that the SWAT-AG performed well and obviously better than the original SWAT in simulating the soil water and salt dynamics, groundwater depth fluctuations, and plant growth and water consumption. The results showed that the NSE averagely increased from −17.57 to 0.57 and from 0.71 to 0.79 for soil water storage and leaf area index, respectively, in typical croplands and natural patches. In addition, the effects of shallow groundwater in sustaining the agro-ecosystems were reasonably revealed with the spatial analysis of evapotranspiration, capillary rise and salt accumulation. The test case proved that the proposed SWAT-AG could efficiently enhance the functionality and practicality of hydrological models for agricultural watersheds with shallow groundwater.