Simulation of groundwater evaporation and groundwater depth using SWAT in the irrigation district with shallow water table

In irrigation districts with shallow water table, groundwater evaporation (ET_gw) and groundwater depth are important variables for the study of water balance. These variables are influenced by natural factors and human activity. In this study, a new method of simulating ET_gw was used for SWAT, and the computing and output modules of groundwater depth were established. In addition, based on simulations, we analyzed the influences of irrigation schedules and soil types on ET_gw and groundwater depth in the Irrigation Districts along the Lower Reach of Yellow River Basin. The applicabilities of the three methods (Hargreaves, Priestley–Taylor and Penman–Monteith) simulating potential evapotranspiration in SWAT 2000 were evaluated by the measured groundwater evaporation, and Hargreaves was applied in the simulation for irrigation district due to its smallest simulation error. The results presented that the mean groundwater depth decreased with the increase of irrigation amount. However, the changes of soil water storage in root zone and groundwater depth might have more complex effects on the variation of the mean groundwater evaporation. Loamy sand had the smallest annual mean groundwater depth and mean annual ET_gw in the study area, while silt loam corresponded to the largest groundwater depth and groundwater evaporation. This study provides a new method for making simulations and analyses of the hydrological cycle in irrigation districts which has a shallow water table.