Streamflow in the Mackenzie Basin, Canada

Rivers of the Mackenzie Basin exhibit several seasonal flow patterns that include the nival (snowmelt dominated), proglacial (influenced by glacier melt), wetland, prolacustrine (below large lakes), and regulated flow regimes. The Mackenzie amalgamates and moderates these regimes to deliver spring peak flows, followed by declining summer discharge and low winter flows, to the Arctic Ocean. The mountainous sub-basins in the west (Liard, Peace, and northern mountains) contribute about 60% of the Mackenzie flow, while the interior plains and eastern Canadian Shield contribute only about 25%, even though the two regions have similar total areas (each occupying about 40% of the total Mackenzie Basin). The mountain zone is the dominant flow contributor to the Mackenzie in both high-flow and low-flow years. A case study of the Great Slave system demonstrates the effects of natural runoff, regulated runoff, and lake storage on streamflow, as well as the large year-to-year variability of lake levels and discharge. Despite a warming trend in the past three decades, annual runoff of the Mackenzie Basin has not changed. Significant warming at most climatic stations in April (and at some, also in May or June) could have triggered earlier snowmelt. The first day of hydrograph rise for the main trunk of the Mackenzie (seen as a proxy for breakup) has advanced by about three days per decade, though the trend was not statistically significant for the mountain rivers. Peak flows do not reveal any trend, but the arrival of the spring peaks has become more variable. More evidence is needed to interpret these flow phenomena properly.