Assessing the potential impacts of climate change on streamflows and water temperatures in a northern Canadian watershed

Directional changes in climate are occurring and largely due to the increasing concentration of greenhouse gases in the atmosphere. Projected changes in precipitation and air temperature will likely have a significant impact on hydrological regimes and thermal conditions within and among river basins. Over the past decade, potential impacts on hydrological regimes have received much attention, but less is known about the associated changes in stream water temperatures, particularly at higher latitudes. Stream temperature plays a critical role in determining the lotic ecosystem function as well as the metabolic rates of organisms and their ability to interact with other species. For example, an increase in stream temperatures may affect water quality dynamics by decreasing dissolved oxygen concentrations and increasing biochemical reaction kinetics in the stream. Therefore, it is essential to characterize the potential impacts of climate change on stream temperatures, which can primarily be achieved through the modeling of physical processes. In this study, we used the Soil and Water Assessment Tool to assess the potential climate change impacts on streamflow and stream temperature regimes in the Mackenzie River Basin in northern Canada. The Mackenzie River is the longest and largest river system in Canada and is a major influence on the global climate and ocean circulation systems. Streamflow and water temperatures were calibrated and validated from 1950-2018 using multi-site observed data. Then, an ensemble of global climate models was used to evaluate the impacts of climate change on streamflow and stream temperature. Results indicate that the magnitude of streamflow and stream temperature changes varies spatially across the watershed. Such changes in thermal regimes in the future will likely affect stream ecosystems and the persistence of freshwater species, thus requiring appropriate management measures to attenuate these impacts.