Climate-Lake Interactions

Lakes cover an estimated 11% of the Mackenzie River Basin (MRB) and they are an integral part of the Basin’s energy and water cycling regime. For convenience they are classified into small, medium and large in terms of surface area. MRB lakes are subjected to a wide range in air temperature from south to north, and to substantial differences in precipitation. The ice-covered period is a function of lake size and location. Small lakes have a longer ice-covered period (6–9 months) than large lakes (4–7 months) and northern lakes have a longer icecovered period than their southern counterparts. Lake ice duration and thickness is strongly influenced by both air temperature and overlying snow depths. During the open water season, for small shallow lakes, the seasonality of convective fluxes is similar to the surrounding land surfaces, but for medium and large lakes there is a large time lag. Their total seasonal evaporation is significantly greater than for terrestrial surfaces and their considerable heat storage capacity accounts for the temporal lag in energy and water cycling. A large lake such as the Great Slave Lake is highly sensitive to interannual climate variability and achieves substantially greater heat storage, higher temperatures and greater evaporative and sensible heat fluxes during a warmer year than during an average year. Instead of exhibiting strong diurnal evaporation cycles, its thermal and evaporative behavior is dominated by synoptic systems that approach a three-day cycle. Mass transfer methods of calculating evaporation works well, but are specific to size of the lake and its exposure to atmospheric forcing. Slab models employed to describe the energy cycles of different size lakes have met with some success. Lakes of all sizes are strongly impacted by climate variability and change and this has large influences on the regional hydrologic regimes.