Climate Change Canada

 

6.3: Surface water levels: lakes and wetlands

In regions of Canada where there are sufficient data, there is no indication of long-term changes to lake and wetland levels. Future levels may decline in southern Canada, where increased evaporation may exceed increased precipitation (low confidence). Projected warming and thawing permafrost has the potential to cause future changes in many northern Canadian lakes, including rapid drainage (medium confidence).

 

Canada has more than 2 million lakes covering 7.6% of the country’s area, with 578 having an area greater than 100 km2 (Canadian National Committee, 1975; Monk and Baird, 2011). There is a wide range of lake types, including the Laurentian Great Lakes (Superior, Michigan, Huron, Erie, and Ontario) and Mackenzie Great Lakes (Great Slave and Great Bear), Arctic and sub-Arctic lakes, glacial, boreal, prairie, and shallow enclosed saline lakes (Schertzer et al., 2004). Some lake levels are monitored by Canada’s Hydrometric Network (see Box 6.1). Other than in a select few cases, there is limited information on past trends and projected future changes in lake levels. Furthermore, many of the larger lakes are regulated by humans, and there is no comprehensive national dataset for unregulated lakes. Thus, a Canada-wide assessment of past trends and future changes is challenging. This section focuses on major lakes and water bodies, reflecting the available literature and monitoring data.

The main inputs include river inflow (runoff), direct precipitation onto the water body, snowmelt, and groundwater inflow. Outputs involve river outflow, evaporation, and exchange with groundwater. The contribution from these variables varies greatly with the size of the water body. Larger lakes within very large drainage basins are affected by events far upstream, in addition to local/regional climate. Smaller lakes and wetlands are more responsive to local climatic conditions. Surface water bodies in Canada are becoming increasingly vulnerable to a variety of stresses, both climate-related and from human management (flow regulation and land-use change) (e.g., Schertzer et al., 2004).

 

6.3.1: Laurentian Great Lakes

Given their importance to Canada and the United States, the Laurentian Great Lakes are among the most studied water bodies in North America. Levels of these lakes have been monitored for more than 100 years by Canadian and US federal agencies. The levels show a large degree of variability due to natural climate variations, as well as to direct human management (e.g., dredging, diversions). These fluctuations have significant impacts on shoreline erosion, flooding of property, navigation, recreation, economy, aquatic ecosystems, and human health. Seasonally, water levels typically progress from a summer maximum to a minimum in the winter/spring (Argyilan and Forman, 2003). The lakes also exhibit year-to-year and multi-year fluctuations of less than 2.0 m, varying by lake (Wilcox et al., 2007; DFO, 2013).

All of the Laurentian Great Lakes have experienced considerable variability in overall NBS and its primary individual components (basin-wide precipitation, lake evaporation, and river runoff) during the last several decades. This year-to-year and multi-year variability is significantly influenced by naturally occurring large-scale modes of climate variability including PDO, AO, and the Atlantic Multi-decadal Oscillation (see Chapter 2, Box 2.5) (e.g., Ghanbari and Bravo, 2008; Hanrahan et al., 2010). Given the large geographic expanse of the Laurentian Great Lakes basin, trends in NBS and individual components vary from one lake to another. In Lake Superior, evaporation is increasing and runoff is decreasing, resulting in a significant decrease in NBS. These trends are also seen for Lake Erie (although not at statistically significant levels). In Lake Ontario, NBS has increased significantly, mainly due to increases in precipitation and runoff, although changes in these individual components are not significant. For the other lakes, trends are insignificant and mixed. For example, runoff is declining for Lake Erie, but rising for Lakes Michigan, Huron, and Ontario. Evaporation has increased over the last 70 years in Lakes Superior and Erie but shows relatively little change in the other lakes (although values have been higher since around 1998). Precipitation has increased in Lake Ontario but decreased in Lake Superior, while no trend is evident in the other lakes.

From 1998 to 2013, all the Laurentian Great Lakes experienced a long period of low levels, including record lows in Lakes Michigan and Huron in December 2012 and January 2013. This period ended with a quick rise in all lake levels starting in 2013. September 2014 was the first month since 1998 that all lakes were above long-term (1918–2013) average levels. The 2013 rise was attributed to increased precipitation, while the 2014 rise resulted from a combination of below-average evaporation and above-average precipitation and runoff (Gronewold et al., 2016). During spring 2017, a series of above-average precipitation events caused the level of Lake Ontario to reach its highest level since reliable measurements began in 1918 (IJC, 2017). These two opposite extremes, occurring within a few years of each other, reveal the variability in the Laurentian Great Lakes’ levels and illustrate the difficulty in projecting future lake levels in response to climate change.

Most studies of future levels have been based on CMIP3 GCM projections (see Chapter 3, Box 3.1) that have been run through RCMs (Angel and Kunkel, 2010; Hayhoe et al., 2010; IUGLS, 2012; MacKay and Seglenieks, 2013). RCMs are essential for modelling the Laurentian Great Lakes, since their finer spatial resolution (typically around 50 km versus GCM grids of around 200 to 250 km; see Chapter 3, Section 3.5) allows explicit modelling of the individual lakes. As a result, models include phenomena that can have significant effects on water balance, such as lake-effect snow, which transfers large amounts of water from the lake to the land surface. Projected NBS shows considerable changes to the seasonal cycle of Lakes Michigan and Huron for 2041–2070 compared with 1961–2000 (see Figure 6.10). These changes include an increase in NBS during the winter and early spring and a decrease in summer and early fall, largely due to projected changes in seasonal precipitation. Other lakes have similar results. Overall, these projected seasonal changes are expected to result in a decrease in NBS of 1.7% to 3.9% in Lakes Superior, Michigan, Huron, and Erie, and of 0.7% in Lake Ontario (IUGLS, 2012). On average, under a range of emission scenarios, most RCM studies project a lowering of future lake levels by 0.2 m for the 30-year time period centred on the 2050s, as compared to the 1971–2000 mean. However, there is a considerable range (from a 0.1 m increase to a 0.5 m decrease) (Angel and Kunkel, 2010; Hayhoe et al., 2010; IUGLS, 2012). These changes are less than those projected using statistically downscaled GCM output that does not incorporate the individual lakes (MacKay and Seglenieks, 2013). All studies agree that there will continue to be large year-to-year and multi-year variability in lake levels, possibly even above and below the historically observed extremes (IUGLS, 2012; Music et al., 2015).