Simulating regional full-chain water balance using a novel surface water-groundwater coupled model

Abstract

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. Results demonstrate that the baseline model, following comprehensive calibration and validation, effectively reproduced the regional hydrological cycle during 2005–2019 and generated complete FCWB outputs. By constructing a general model under long-term average annual precipitation scenarios based on the baseline model, comparison of water balance outputs between the two models revealed that groundwater storage change shifted from 0.11 billion m³ in the baseline scenarios to −0.31 billion m³ in the general scenarios. This indicates that recent groundwater recovery is attributable to anomalously high precipitation, rather than the resolution of the groundwater overdraft problem, thereby strengthening water managers' determination to continue promoting the remediation of groundwater depletion.