A Multi-Approach Framework to Couple Independent Models for Simulating the Interaction between Crop Growth and Unsaturated-Saturated Flow Processes

Land surface and groundwater table are two key hydrologic boundaries for the water transfer from atmosphere to aquifer. Their functioning is strongly affected by the water flow through the unsaturated zone. Quantification of soilmoisture processes is a prerequisite for accurate watershed-scale groundwater modelling. Moreover, soil-moisture processes are affected by vegetation and crop growth. In many cases, the unsaturated zone has been simplified or even neglected in groundwater modelling. Depending on the depth to groundwater, the unsaturated zone cannot be neglected in every case. In shallow groundwater, capillary rise can further play an important role. It can lead to an increase in ET, thus producing a feedback between crop growth and groundwater flow. In order to simulate all the processes involved, it is important to integrate them by coupling sub-modules for the relevant processes. There are various codes to simulate vegetation and crop growth, unsaturated and saturated zone flow simultaneously in an integrated manner. However, these solutions are not sufficiently flexible for all cases. Therefore, in this paper we integrated WOFOST, a crop growth and production model, with HYDRUS-1D, an unsaturated flow model, and with MODFLOW, a saturated flow model. The coupling was done using a combination of two different approaches, external coupling (through input/output data manipulation) and with code wrapping. We used OMS3 for wrapping WOFOST, and PYTHON to write scripts. The model was tested in a synthetic case where the importance of a coupled model was shown, especially in areas with shallow groundwater.