Enhancing Winter Climate Simulations of the Great Lakes: Importance of Integrating 3D Hydrodynamics with a Regional Climate Model

The Laurentian Great Lakes play a significant role in the climate of the Midwest and Northeast United States due to their vast thermal inertia, moisture source potential, and unique heat and moisture flux dynamics. Using a fully three-dimensional (3D) lake-ice-atmosphere coupled modeling system for the Great Lakes, this study focuses on the Great Lakes' winter climate simulation and investigates the crucial question about what are the key lake processes influencing lake thermal structure and ice cover that are missed by one-dimensional (1D) lake models but effectively captured by 3D lake models. By integrating 3D lake hydrodynamics, the regional climate model demonstrates superior performance in reproducing observed LSTs, ice cover distribution, and the vertical thermal structure of the Great Lakes, as well as enhanced simulation of over-lake atmospheric conditions, including air temperature, wind speed, and sensible and latent heat fluxes, underscoring the importance of resolving complex lake dynamics for reliable climate projections. More importantly, through process-oriented numerical experiments, we identify key 3D hydrodynamic processes—ice transport, heat advection, and shear production in turbulence—that explain the superiority of 3D lake models over 1D lake models, particularly in cold season performance and lake-atmosphere interactions for the Great Lakes system. This research underscores the necessity of incorporating 3D hydrodynamic models in RCMs to improve our predictive understanding of the Great Lakes' response to climate change. The findings advocate for a shift towards high-resolution, physics-based modeling approaches to ensure accurate future climate and limnological projections for large freshwater systems.