Hydroclimatic controls on water balance and water level variability in Great Slave Lake

On average, 86% of riverine discharge to Great Slave Lake, Northwest Territories, Canada, was gauged during the period 1964–1998, offering an unprecedented opportunity to study and understand controls on water balance of a large northern lake at the headwaters of the Mackenzie River. A functional daily water balance model, incorporating measurements of riverine inflow, precipitation on the lake surface, evaporation, and riverine outflow was developed, which predicts the amplitude and frequency of annual water level fluctuations, and closes the water balance to within ± 6% for 28 of 35 years and ± 11% for the remaining 7 years, with an overall systematic error of + 2%. Annual water balance estimates for the period 1964–1998 reveal that about 74% of inflow into Great Slave Lake originates from the Peace‐Athabasca catchments that enter the lake via the Slave River, whereas 21% is derived from other catchments bordering Great Slave Lake, and 5% from precipitation on the lake surface. An estimated 94% of water losses occur by riverine outflow to the Mackenzie River and 6% by evaporation from the lake surface. The primary driving force behind water level fluctuations in Great Slave Lake, including the post‐regulation period following development of the W.A.C. Bennett Dam, is shown to be climate‐driven precipitation variability in the Peace‐Athabasca basins. A simple precipitation regression model is developed to simulate water level fluctuations in Great Slave Lake over the past 100 years. Copyright © 2006 John Wiley & Sons, Ltd.