Hydrology of the Northwestern Subarctic Canadian Shield

The Canadian Shield occupies about one-third of Canada’s land area, one-fifth of the Mackenzie Basin, and contains much of Canada’s freshwater resource. The northwestern portion of the Shield has a relatively dry, subarctic climate and a heterogeneous landscape comprising exposed bedrock uplands, soil mantled slopes, wetlands and lakes. The water budget of bedrock uplands is influenced by rock fractures, slope aspect, precipitation or melt intensity, and storage capacity. The lateral transfer of runoff from exposed bedrock is crucial to the hydrology of downslope soil-filled areas where the water maintains storage to sustain evaporation and support streamflow generation. Headwater lakes are an important store of water that must be recharged to storage capacity prior to yielding outflow to higher order streams. Even in perennial streams, flow thresholds must be exceeded before runoff generated in headwaters can be transferred to basin outlets. The subarctic Shield environment has large spatial and temporal variations in available storage, where the hydrologic connectivity that dictates runoff response is controlled in part by the geometry and spatial distribution of landscape components. Streamflow regime may be dominated by snowmelt runoff from the land (nival regime) or modified by storage effects of lakes along the channel network (prolacustrine regime).