Using a linked APSIM-MODFLOW model framework to quantify the impact of irrigation frequency on groundwater level in a typical groundwater over-exploitation region of NCP

Efforts to slow down groundwater depletion requires reliable estimates of the impacts of irrigation on shallow groundwater levels. However, spatial assessment of the effects of irrigation schedule on groundwater level change is still lacking. Here, we present a linked APSIM-MODDLOW model framework to reveal irrigation-groundwater linkages in the plain area of Ziyahe River Basin by considering irrigation schedules, crop yield, ETa and leakage. The linked APSIM-MODLFOW model effectively simulates grain yield and regional groundwater level fluctuations in the winter wheat-summer maize cropping system of the NCP. We found that the simulated grain yield and evapotranspiration increase rapidly with the increase of irrigation frequency, whereas the yield exhibits a gradual increase when irrigation exceeds three times (70 mm each time). The simulated regional average groundwater levels exhibit an increase under rain-fed and single-irrigation scenarios-with irrigation applied at the jointing stage of wheat-whereas a decline is observed under alternative irrigation regimes. These findings indicate that regional groundwater can be replenished through recharge when irrigation schedules range from single-irrigation (applied at the jointing stage of wheat) to double-irrigation (applied at both the jointing stage and the flowering and grain-filling stage of wheat) The unconfined aquifer maintains extraction-recharge equilibrium under the irrigation amount 70 – 140 mm (1-irrigation to 2-irrigations). Spatial distribution of groundwater flow field revealed that to prevent a decline in regional groundwater levels and reduce grain yield loss, the existing 3-irrigations schedule should be maintained in the southern region of study area and Shijin Irrigation District, while a 1-irrigatoin schedule should be implemented in the northern region. These findings can serve as a reference for regional irrigation and groundwater resource evaluation and management. The linked model framework has important implications for other studies where groundwater variations are highly impacted by agriculture irrigation.