Hydrodynamic Modelling of Great Slave Lake Using NEMO

The subarctic region of northern Canada, including the Mackenzie River basin is deeply impacted by the changing climate. Unprecedented rates of warming in Canada’s North, up to four times the global average, have been observed in the region over the past few decades. This brings significant implications for regional hydrology, ecosystems, and human activities. A major controlling feature in the Mackenzie River Basin is Great Slave Lake, which is the second largest lake in the Northwest Territories of Canada and the deepest lake in North America. With over 60% of the population of Northwest Territories living along its shores, Great Slave Lake is a vital ecological and societal asset in the region. This study aims to further our understanding of water circulation and stratification patterns in Great Slave Lake through numerical simulation. Despite the status of Great Slave Lake as one of the largest and deepest lakes in North America, comprehensive numerical modelling has proven difficult due to lack of accurate bathymetric data. To address this gap, we collaborated with the Department of Fisheries and Oceans to develop the first complete bathymetric map of Great Slave Lake. Historical naval charts and field sheets were integrated with additional sounding data to produce a simulation domain tailored to the Nucleus for European Modelling of the Ocean (NEMO) at a horizontal resolution of 1km with 30 vertical layers. The NEMO model was chosen for application in this large lake for consistency with the existing model setup being used by Environment and Climate Change Canada (ECCC) for its operational forecasting system in the Laurentian Great Lakes. Atmospheric reanalysis is provided by ECCC’S Regional Deterministic Reanalysis System (RDRS), while surface runoff entering the lake is driven by the Community Environmental Modelling System – Surface & Hydrology (MESH) outputs from the Global Water Futures reanalysis efforts. The resulting NEMO model shows good capability of simulating lake processes with preliminary results indicating that the lake exhibits seasonal thermal stratification, consistent with dimictic behaviour, where full vertical mixing occurs twice annually. Our results also show that wind-induced mixing appears to also play a significant role in lake circulation, and a counterclockwise circulation pattern is observed, with prominent gyres in the main basin of the lake. Ongoing work focuses on further validation of the temperature profiles at select locations and sensitivity analysis to improve the overall simulation capabilities of the model for future water resource management needs.