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Physics-based miniensembles of Weather Research and Forecasting (WRF) Model configurations have been employed to investigate future precipitation changes over the Great Lakes basin of eastern North America. All physics configurations have been employed to downscale multiple distinct Community Earth System Model, version 1 (CESM1), simulations driven by the representative concentration pathway 8.5 (RCP8.5) radiative forcing scenario, spanning a range from moderate (2045–60) to considerable (2085–2100) climate change. Independent of the physics configuration employed, all projected future precipitation changes are characterized by a general increase and a fattening of the tail of the daily rainfall distribution by the end of the century. The fattening of the tail can however be masked by natural variability in the case of the moderate warming expected by midcentury. The heavy-rainfall-derived precipitation increase is projected to be larger than or equal to the Clausius–Clapeyron thermodynamic reference of 7% increase per degree Celsius of surface warming, whereas the increase of average-rainfall-based precipitation becomes limited only for the largest global warming projections. This limitation is dramatically illustrated in one physics configuration at the end of the century. By downscaling the results obtained from the initial-condition ensemble, it is demonstrated that the extreme drying of the Great Lakes basin region characteristic of the most extreme end member of the CESM1 ensemble is significantly modified by downscaling with the version of WRF coupled to the Freshwater Lake model (FLake) of lake processes. This result does, however, depend upon the physics configuration employed in WRF for the parameterization of processes that cannot be explicitly resolved. [ABSTRACT FROM AUTHOR]

Accurate identification of the impact of global warming on water resources in major river systems represents a significant challenge to the understanding of climate change on the regional scale. Here, dynamically downscaled climate projections for western Canada are presented, and impacts on hydrological variables in two major river basins, the Fraser and Athabasca, are discussed. These regions are both challenging because of the complexity of the topography and important because of the economic activity occurring within them. To obtain robust projections of future conditions, and to adequately characterize the impact of natural variability, a small initial condition ensemble of independently downscaled climate projections is employed. The Community Earth System Model, version 1 (CESM1), is used to generate the ensemble, which consists of four members. Downscaling is performed using the Weather Research and Forecasting Model, version 3.4.1 (WRF V3.4.1), in a nested configuration with two domains at 30- and 10-km resolution, respectively. The entire ensemble was integrated for a historical validation period and for a mid-twenty-first-century projection period [assuming representative concentration pathway 8.5 (RCP8.5) for the future trajectory of greenhouse gases]. The projections herein are characterized by an increase in winter precipitation for the mid-twenty-first-century period, whereas net precipitation in summer is projected to decrease, due to increased evapotranspiration. In the Fraser River basin, a shift to more liquid precipitation and earlier snowmelt will likely reduce the seasonal variability of runoff, in particular the spring freshet. In the Athabasca River basin, winter precipitation and snowmelt may increase somewhat, but increasing evapotranspiration may lead to reduced streamflow in late summer. [ABSTRACT FROM AUTHOR]

• An integrated hydrological model is used to examine climate change impacts. • Predicted hydrologic change varies in both magnitude and direction. • Diverse meteorological forcing reveals the importance of lake-effect consideration. • Insight is gained with regards to the temporal resolution of climate forcing data. Climate change in the Great Lakes Basin of North America is expected to have a profound impact on hydrological processes. A greater understanding of these impacts must be developed to inform future adaptation strategies. This study aims to assess potential watershed response to changing climate conditions in southwestern, Ontario, Canada using the fully integrated surface-subsurface model HydroGeoSphere. To account for the uncertainty associated with climate projections and capture a range of possible conditions, a diverse set of meteorological forcings are used, including projections derived from Regional Climate Models (RCMs), a synthetic scenario based on IPCC fifth assessment report predictions, and temporal analogues. Simulation outputs have been compared to assess the potential influence of changing climate on groundwater hydraulic head, surface discharge, and net fluid exchange between surface and subsurface domains. The modelled projections reveal variability in both direction and magnitude of predicted hydrologic change suggesting that simulation outcomes should be interpreted probabilistically, and climate projection uncertainty needs to be characterized. Nonetheless, model outcomes reveal a greater likelihood for a significant reduction in mid-century discharge relative to any significant change in groundwater head or net exchange flux. This study also examines the influence of meteorological input with different temporal resolutions and the importance of RCM lake model coupling for capturing the regional climate influence of the Great Lakes. The latter of these considerations was found to influence spring and summer hydrologic phenomena while the former showed that both daily and monthly normal forcing yield comparable results, if monthly aggregated model outputs are considered. These findings are important for informing the design of future hydrologic investigations especially when working with computationally intensive, large-scale integrated models. [ABSTRACT FROM AUTHOR]