Climate Change Canada

 

5.5: Lake and river ice

The duration of seasonal lake ice cover has declined across Canada over the past five decades due to later ice formation in fall and earlier spring breakup (high confidence). Seasonal maximum lake ice cover for the Great Lakes is highly variable since 1971 (very high confidence), with no significant trend.

Spring lake ice breakup will be 10 to 25 days earlier by mid-century, and fall freeze-up 5 to 15 days later, depending on the emissions scenario and lake-specific characteristics such as depth (medium confidence).

Canada is a lake-rich country, particularly across the north, with approximately 20% to 25% of the Arctic coastal lowlands covered by lakes (Duguay et al., 2003). Therefore, the timing of lake and river ice freeze-up and breakup (known as ice phenology) and ice thickness are important indicators of climate variability and change. Ice phenology is sensitive to changes in air temperature, whereas changes in ice thickness are linked to changes in both air temperature and snowfall. Due to the insulating properties of snow, the timing of snow accumulation on new ice and the seasonal accumulation of snow influence ice thickness. In situ records of ice cover across much of Canada are limited, because surface-based ice monitoring is not practical in many regions, so satellite remote sensing is commonly used to monitor lake and river ice (Howell et al., 2009).

Changes to ice phenology and thickness influence the role that lakes play in regional energy and water cycles (Rouse et al., 2005). Ice cover also has strong effects on lake biogeochemical processes in cold regions: changes in the ecological productivity of high Arctic lakes on Ellesmere Island are predominantly determined by variations in ice cover duration (Griffiths et al., 2017). Reductions in ice cover may also allow greater emissions of methane (a greenhouse gas) from Arctic lakes (Greene et al., 2014; Tan and Zhuang, 2015). The importance of ice cover to ecosystems is not limited to the Arctic. For instance, earlier ice melt across the Great Lakes is linked to turbidity and phytoplankton activity through enhanced wind-induced mixing (Bai et al., 2015). Seasonal roads across frozen lakes serve as a critical supply lines to remote communities and mines during winter months, while stable lake and river ice is a necessity for safe winter season recreation and travel for residents of northern communities.

 

5.5.1: Observed changes in lake and river ice

Surface observations show that ice breakup is occurring earlier, and freeze onset later, across small lakes in southern Quebec, Ontario, Manitoba, and Saskatchewan (Brown and Duguay, 2010). A significant declining trend in annual maximum ice cover was observed for the Laurentian Great Lakes over the 1973–2010 period (71% decline for all of the Laurentian Great Lakes), with the largest declines occurring in Lake Ontario (88%), Lake Superior (79%), and Lake Michigan (77%) (Wang et al., 2012). Heavy ice years in 2014, 2015, and 2018, however, result in no trend over the full 1973–2018 period (Figure 5.14). The large year-to-year variation is associated with the Arctic Oscillation/North Atlantic Oscillation (AO/NAO) and El Niño–Southern Oscillation (ENSO) (see Chapter 2, Box 2.5). For example, the record-breaking low in maximum ice cover in the winter of 2011/2012 occurred during a strong positive-phase AO/NAO and the cold phase of ENSO (La Niña event) (Bai et al., 2015). Whether variable ice cover contributes to observed increases in water temperature in the Laurentian Great Lakes is a topic under debate. Recent findings suggest that changes in winter lake ice cover play only a minor role in the observed warming trend (Zhong et al., 2016), whereas ice cover duration was linked to summer surface water temperature (particularly in nearshore areas) when the lakes were examined at a finer spatial scale (Mason et al., 2016).

Satellite measurements show that lakes in Arctic Canada have also been experiencing an earlier ice minimum (the last date of floating ice cover on the lake surface) and an earlier date when the water is clear of ice (see Figure 5.15; see also Duguay et al., 2006; Prowse, 2012; Cooley and Pavelsky, 2016). These changes are consistent with a recent circumpolar assessment, which showed that approximately 80% of Arctic lakes experienced declines in ice cover duration from 2002 to 2015, due to both a later freeze-up and an earlier breakup (Du et al., 2017). Results from northern Alaska (which are likely similar to those in northwestern Canada) show that lake ice has begun to thin in recent decades (Alexeev et al., 2016). From 1992 to 2011, approximately one-third of shallow lakes in which the entire water volume historically froze to the bed by the end of winter had changed to floating ice (Arp et al., 2012; Surdu et al., 2014). Canada’s northernmost lake, Ward Hunt Lake (located on Ward Hunt Island), had maintained stable, continuous year-round ice cover for many decades until very warm summers of 2011 and 2012, when the ice cover fully melted (Paquette et al., 2015). This loss of inland perennial freshwater ice cover occurred nearly simultaneously with the collapse of the nearby Ward Hunt ice shelf (Mueller et al., 2009; Veillette et al., 2010). Analysis of a 15-year time series (1997–2011) of radar and optical satellite imagery provides further evidence that some lakes in the central and eastern Canadian high Arctic are transitioning from continuous (year-round) to seasonal ice cover (Surdu et al., 2016).

It is difficult to provide an assessment of river ice changes across Canada because of sparse observations and a lack of recent assessments of the available data. There is evidence of earlier river ice breakup, consistent with increases in surface temperature (Prowse, 2012). However, the impact that climate-driven changes in ice phenology and thickness, combined with changing seasonal flow regimes (see Chapter 6, Section 6.2) and the influence of hydraulic processes (i.e., changing ice strength), will have on ice jams and flood events is not fully understood (Beltaos and Prowse, 2009).

 

5.5.2: Projected changes in lake and river ice

Changes in lake ice can be projected only indirectly, because lake models are not embedded within global climate models and individual lakes are not spatially resolved. When forced by a future climate under a medium emission scenario (RCP4.5), lake ice models project that spring breakup will occur between 10 and 25 days earlier by mid-century (compared with 1961–1990), and freeze-up will be five to 15 days later across Canada (Brown and Duguay, 2011; Dibike et al., 2012) (Figure 5.16). This results in a reduction of ice cover duration of 15 to 40 days for much of the country. More extreme reductions of up to 60 days are projected in coastal regions. The range in projected changes is due to regional variability in temperature and snowfall changes, and to lake-specific variables such as size and depth. The Laurentian Great Lakes can be resolved by lake models if the projected climate forcing data are downscaled. This approach has identified consistent results, with reduced ice cover duration of between 25 to 50 days across the Laurentian Great Lakes by mid-century, due to both later freeze-up and earlier melt (Gula and Peltier, 2012). Mean seasonal maximum ice thickness is projected to decrease by 10 to 50 cm by mid-century, with a more pronounced decrease in the eastern Canadian high Arctic (Brown and Duguay, 2011).

Warming is projected to drive an earlier river ice breakup in spring, which is due to decreased mechanical ice strength and earlier onset of peak discharge (Cooley and Pavelsky, 2016). More frequent mid-winter breakup and associated ice jam events are anticipated (Beltaos and Prowse, 2009), although projected changes in river ice properties may reduce ice obstructions during the passage of the spring freshet (the increased flow resulting from snow and ice melt in the spring) (Prowse et al., 2010). A shorter ice cover season and reduced ice thickness may affect food security for northern communities by reducing the reliability of traditional icebased hunting routes and the safety of ice-based travel. The reliability and predictability of ice roads as supply lines to northern communities and development sites is not fully dependent on climate, because these ice roads are partially engineered each season (i.e., snow is removed to accelerate ice growth). However, there have been instances of severely curtailed ice-road shipping seasons due to unusually warm conditions in the early winter (Sturm et al., 2016). The seasonal operational duration for such ice roads is expected to decrease as a result of winter warming (Perrin et al., 2015; Mullan et al., 2017).