How Spatial Resolutions Impact the Large-Scale River Hydrodynamic Model Simulations: Analysis Focuses on Model Physics

Abstract

Large-scale hydrodynamic models are vital for flood risk assessment and understanding the global water cycle; however, their results can include uncertainties related to spatial resolution. Few studies have evaluated hydrodynamic models across a range of spatial resolutions, with most focusing on a few variables (e.g., discharge) and often neglecting performance at ungauged sites or the role of parameter optimization. We addressed these limitations by comparing Catchment-based Macro-scale Floodplain (CaMa-Flood) model simulations in the Amazon River basin at different spatial resolutions, using the higher resolution as a benchmark in each comparison. We found good inter-resolution performance in simulating discharge and water depth, with coefficients of determination exceeding 0.88 in >80% of locations. The normalized Nash–Sutcliffe efficiencies for discharge and water depth were greater than 0.83 and 0.68, respectively, in more than 75% of locations, suggesting that most locations had consistent hydrodynamics. We detected large discrepancies in discharge between simulations at ∼2.5% of locations due to limited representation of bifurcation flow, floodplain conveyance, and backwater at river confluences in the model. Water depth also differed significantly at ∼3% of locations, mainly at headwaters, due to width bottleneck sections. Flood extent patterns differed minimally between simulations around the main stream and large sub-streams, whereas improvements in the downscaling method are required for small sub-streams. Our results demonstrate the need to improve the representation of bifurcation channels and floodplain parameterization for specific locations, although the general river hydrodynamics patterns were well-captured by computationally efficient moderate-resolution (i.e., 6 arcmin) CaMa-Flood simulations.