This study aims to assess the impact of climate change on water resources in a large watershed within the Laurentian Great Lakes region using the fully integrated surface-subsurface model HydroGeoSphere. The hydrologic model is forced with an ensemble of high-resolution climate projections from the Weather Research and Forecasting (WRF) model, which has been extended with the interactive lake model FLake to capture the effects of the Great Lakes on regional climate. The WRF ensemble includes two different moist physics configurations at resolutions of 90, 30, and 10 km, as well as four different initial and boundary conditions to control for natural climate variability. The integrated hydrologic model is run with a representative seasonal cycle, which effectively constrains natural variability while remaining computationally feasible for a large-scale model. The impacts of climate model resolution and bias correction are also investigated. The two WRF configurations show opposite responses in summer precipitation but similar trends for other seasons. Hydrologic simulations generally follow the climate forcing; however, due to subsurface memory, summer differences propagate across the entire seasonal cycle. This results in dry scenarios with reduced streamflow and water availability throughout the year, and wet