Advancing global river hydrodynamics simulations by catchment-based macro-scale floodplain modeling approach

Abstract Water flows from high to low elevation, a fundamental principle governing surface hydrodynamics. Despite its simplicity, representing this physical reality in large-scale river models has long been a challenge, primarily due to the multiscale nature of river–floodplain interactions and the limitations of grid-based modeling frameworks. Traditional global hydrological and flood models often sacrifice physical consistency for computational efficiency, leading to unrealistic water routing, especially in low-relief regions where floodplain dynamics are critical. In recent years, Catchment-based Macro-scale Floodplain modelling approach (CMF approach) have emerged as a promising method to address this challenge. By discretizing the river network into sub-catchments and incorporating sub-grid-scale floodplain topography through parameterized elevation–storage relationships, these models enable efficient simulations that maintain the core physical rule: water must flow downhill. Notable implementations such as CaMa-Flood, MGB-IPH and HyMAP have demonstrated the ability to realistically reproduce inundation extent, surface water levels, and discharge variability simultaneously at continental to global scales. The physically consistent representation of floodplain hydrodynamics combined with high-precision topography data has expanded the range of applications for global river models. By producing water surface elevations and inundation patterns that align with realistic terrain gradients, CMF approach enables direct comparison with satellite observations such as altimetry and surface water extent, supporting both validation and data assimilation. This physical fidelity also enhances the credibility of global flood hazard and risk assessments, especially in low-relief and data-scarce regions. Furthermore, the explicit simulation of floodplain storage and exchange facilitates coupling with ecosystem and biogeochemical models, opening new avenues for research on wetland hydrology and carbon-water interactions. Thus, the CMF approach forms a versatile foundation for physically grounded, observation-aware Earth system applications.