Simulating Regional Full-Chain Water Balance Using a Novel Surface Water-Groundwater Coupled Model

The water balance serves as the foundation for hydrological and water resources research and practice. However, there have been few systematic and detailed studies on the regional water balance itself. In this study, the concept of the full-chain water balance (FCWB) is proposed for the first time, and a new surface water-groundwater coupled model is used to simulate and analyze it. Firstly, we coupled a semi-distributed hydrological model and a groundwater numerical model through spatiotemporal connection and information interaction, developed a FCWB simulation mechanism at multiple hierarchies and multi-spatiotemporal scales, and carried out a verification application in the Sanjiang Plain, China. During the model development and construction, several errors occurred in the FCWB. Through error diagnosis, tracing, and backtracking, we successfully resolved bugs in the code and issues in the input data. Subsequently, the model parameters were calibrated from three aspects: surface runoff in hilly areas, groundwater heads in plains, and irrigation volumes. Meanwhile, attention was paid to the changes of water inputs and outputs in the FCWB to ensure that main fluxes could match the existing research and evaluation results published in the region. This achieved a comprehensive calibration, rather than just calibrating partial hydrological processes that gaged. The results show that the model effectively reproduces the hydrological cycle from 2005 to 2019, and forms a detailed FCWB of the entire region, which also provides abundant information and holistic perspective for the thorough analysis of the hydrological evolution characteristics and water resources issues in the modeling area.