Degrees of Change – Water Resources
2.0 The NRTEE’s Degrees of Change diagram: Illustrating the Impacts of Climate Change in Canada
Water Resources
| Previous | Table of Contents | Next |
This category includes freshwater systems (rivers, ponds, lakes, glaciers, snowpack, reservoirs, groundwater aquifers) and sources that replenish them. Although we recognize the important connections between surface and groundwater flows, here we highlight effects on surface waters. With only half of one per cent of the world’s population, Canada currently has 20% of the world’s stock of surface freshwater, and our average annual renewable freshwater supply or water yield is 3,472 km2 — the third largest in the world.[63] Within Canada, most people live along the southern border and much of the economic activity occurs there, yet the majority of surface water flows to the north.
Access to clean, sustainable supplies of water is essential for the health of Canadians and for the functioning of economic activities and sectors. Water scarcity is not a national problem in Canada, but seasonal variability and demand from multiple users already present management challenges in important agricultural regions (e.g., south-central Prairies and southwestern British Columbia). In Changing Currents, the NRTEE concluded that economic and population growth, coupled with anticipated effects of climate change, will impact Canada’s freshwater systems and create new pressures on the long-term sustainability of our water resources.
Warmer average temperatures affect precipitation patterns and evaporation rates, as well as the frequency, intensity, and duration of extreme weather and climate events like droughts, heat waves, and storms. A national picture of the potential effects on water is challenging to develop: effects will be highly localized, influenced in part by natural processes that regulate hydrology.
 |
What we can expect
BOTH LESS AND MORE WATER SUPPLY.
Changes in precipitation patterns are already evident, with, on average, 20 more days with rain in Canada today compared with the 1950s.[64] In a warmer world, we can expect further changes to the amount and timing of precipitation and to regional hydrology. Overall precipitation is expected to increase slightly in the north and east, and decrease slightly in the south and west, with less in summer, and more as intense events.[65] Studies project increasing runoff in Québec, Newfoundland and Labrador, and the Territories as global temperatures rise up to around 3°C above pre-industrial levels.[66]
Freshwater systems reliant on snow and ice accumulations for replenishment are likely to see dwindling supplies, particularly in summer months. Mountain glaciers in Canada are already shrinking. Studies show an increase in runoff associated with melting glaciers,[67] with runoff declining as glaciers disappear. Some western basins may have already experienced an increased flow phase from glacial melt.[68] At global average temperatures about 2 to 4°C above pre-industrial levels western glaciers could shrink significantly, with smaller glaciers at risk of disappearing.[69]Snow accumulations in alpine areas and across the Prairies are also likely to diminish.[70] Parts of British Columbia and the Prairie provinces will likely experience decreasing supplies and shifts in streamflow timing to earlier in the year, facing increasing water shortages as a result.
Changes in seasonal variability and air moisture also affect regional water availability. For example, despite projections of a rise in precipitation in Maritime provinces, seasonal and yearly variations in precipitation will combine with higher evapotranspiration rates to induce drier summer conditions.[71] In the Prairies, lower spring and summer stream flows are likely to occur in what is already a dry region, increasing both soil water deficits and surface water deficits.[72] At global temperature rises of about 2°C to 3°C, flows in the South Saskatchewan River basin could see significant declines.[73] Studies project drier conditions in the Prairies, with the area of land at risk of desertification increasing 50% by mid-century,[74] and drought frequency doubling at global average temperatures 3 to 4°C above pre-industrial levels.[75]
WATER STRESS AND COMPETITION OVER ACCESS AND USE OF WATER.
Water stress and related restrictions in use are a result of mismatches between available supplies and demands for water. A few locations in Canada are already facing restrictions in water use. For example, in August 2006, the Alberta government stopped accepting applications for new allocations of water in the Oldman, Bow, and South Saskatchewan sub-basins. Climate change affects both the amount of water available for use and the demand for the resource. In the Okanagan region of British Columbia, climate change is expected to both cause changes to runoff and increase irrigation demand, leading to challenges for water managers in maintaining adequate supply[76] while ensuring water quality and ecosystem health. Lower water levels in the Great Lakes, which some climate scenarios project, will likely restrict municipal water use.[77]
Reduced seasonal water supplies and increased demands over the next several decades could enhance competition among water users and lead to conflict in some basins.[78] This has implications for complying with water sharing agreements between Canadian jurisdictions and between Canada and the United States,[79] with the potential to increase the level of current conflicts and create new ones heightening at global average temperatures 2°C and above.
| BOX 7: WARMER GREAT LAKES WATERS |
|
Covering an area of over 240,000 km2, the Great Lakes system contains one-fifth of the world’s stored freshwater, and important coastal wetlands, fish and water fowl populations, while also supporting a variety of activities including shipping and transportation, commercial and recreational fisheries, agriculture, and hydroelectric generation. One in three Canadians and one in eight Americans live in the region surrounding the Great Lakes. Evidence suggests that warmer air temperatures are changing some physical characteristics of the Great Lakes. Average surface temperatures of all lakes in the system have increased over the past decades. Between 1968 and 2002, Lake Huron warmed 2.9°C, Lake Ontario and Lake Erie warmed 1.6°C and 0.9°C, respectively, over the same timeframe. Since 1980, surface waters of Lake Superior are 2.5°C warmer. The duration of ice cover is also declining, further contributing to the warming of Great Lakes waters. Among other ecological effects, the warming trend will favour production of warm-water fish (such as bigmouth buffalo and flathead catfish) over cool- and cold-water fish (such as lake trout). Sources: Dobiesz and Lester (2009); Austin and Colman (2007); Assel (2005); The Great Lakes: Basic Information – http://epa.gov/greatlakes/basicinfo.html. Map adapted from Chiotti and Lavender (2008) 
|
Declines in supplies of water — because of increasing evaporation rates, changing precipitation patterns, increasing demand, or all of the above — affect the quality of water. Warmer air temperatures affect the chemistry of water bodies, contributing to thermal layering in the water column, accelerating plant and animal use of dissolved oxygen, and resulting in oxygen depletion.[80] Less water reduces the ability of water bodies to dilute chemical pollutants and nutrients, which among other effects, diminishes the taste and smell of our drinking water.[81] An increase in the frequency of intense rainfall events, as is expected in a changing climate, increases the risk of water contamination carried by runoff from urban and rural waste and nutrients.
[82] Water quality would likely suffer in some Canadian regions with warming beyond that experienced over the 20th century.[83]
What we can do about it
Continued access to clean water is important for households, industry, communities, and governments. As managers and stewards of water resources, provincial and territorial governments are already developing or introducing water management programs, mostly to deal with existing issues related to supplies and demands. For example, the Ontario Clean Water Act (2006) requires local authorities and stakeholders to develop source protection plans for individual watersheds, including assessments of how much water is available within each watershed.
Effective water conservation and management strategies will need to incorporate changes in moisture and shifts in demand associated with climate change, including demand for potable consumption, irrigation, hydroelectric generation, and other industrial uses, and consider in-stream ecosystem needs as well. The implications of climate change effects on water resources will also need to factor into renegotiation of water-sharing agreements. Within industry, levels of awareness of and concern about the impacts of climate change on water availability differ across sectors, but incorporating uncertainty of climate change projections into management practices is a common struggle.
Adaptive strategies include developing and applying technologies for efficient water use, and changing water use behaviour. Governments can implement programs and policies to shift water use and consumption patterns, including pricing regimes, updating permitting requirements, and providing information on best practices.
________________
Footnotes
63 Statistics Canada (2010).
64 Vincent & Mekis (2006).
65 Bruce et al. (2000).
66 Milly et al. (2005) show increasing run off in the territories, and in Quebec and Newfoundland and Labrador in 2050 based on SRES A1B. Similar results are found in a global assessment by Falloon et al. (2006). There is already some evidence for increasing run-off in the Northwest Territories (St Jacques & Sauchyn 2009), so we place the impact “Run-off in northern and eastern Canada increasing” on the diagram using a range that reflects the current limited observations and the projections for 2050 (upper end of likely range for A1B scenario). Note that there is some contention in the cold region hydrology community that the increases in river flow detected, presumably on account of permafrost degradation in the once instance (St Jaques and Sauchyn), may be because of less water going into storage because river ice formation and growth is retarded under a warming influence (M. Demuth, personal communication, April 1, 2010).
67 Jansson et al. (2003); Pietroniro et al. (2006); Fleming and Clarke (2005).
68 The early increase in glacier run-off may have already occurred in some basins (Demuth and Pietroniro [2003]; Stahl and Moore [2006]; Comeau et al,[ 2009]). Evidence supporting the past peak decline notwithstanding, a period of flow enhancement may not be out of the question. Rigorous hydrological modelling estimates using best possible estimates of future glacier cover scenarios have yet to be produced (M. Demuth, personal communication, April 1, 2010).
69 The end of temperature range (around 4°C) for this impact on the degrees of change diagram corresponds to the expected decline in glacier volumes (see Error! Reference source not found. under Ice, snow and sea).
70 For example, Lapp et al. (2005) project substantial decreases in spring runoff due to a decline in snowpack in watersheds in western Canada. This has significant implications for seasonal flows.
71 Vasseur & Catto (2008).
72 Martz et al. (2007); Bruce et al. (2000).
73 Martz et al. (2007) estimated a 2–36% decrease in surface water availability in a 2 x CO2 scenario. Pietroniro et al. (2006) estimate an 8.5% decrease in flows in the 2050s. Taking into account both estimates, we position the impact statement on the Degrees of Change diagram between 1.9 and 2.8°C (best estimates for range of SRES scenarios for 2050s, reading off AR4 WGII Figure TS4 and represented relative to pre-industrial levels). These studies are consistent with the findings of Milly et al. (2005) and Falloon et al. (2006).
74 Sauchyn et al. (2005) calculated the aridity index for the Prairies in 2050 under a B2 scenario and projected that the area of land at risk of desertification will increase 50% by mid-century. We used likely range for B2 scenario to plot this impact on the Degrees of Change diagram.
75 Early studies suggested that prairie drought frequency could double with a 2x CO2 warming scenario (Williams et al. 1988; this corresponds to approximately 550ppm CO2 at 2080s, which is about 2.6°C according to AR4 WGII Figure TS4 and represented relative to pre-industrial levels). More recent projections (Sheffield and Wood [2007]) show a doubling to quadrupling in the frequency of droughts lasting 4–6 months for Western North America (including the prairies), and a slight increase in drought frequency for Eastern Canada for the A1B and A2 scenarios by the end of the 21st century. They found smaller increases in the frequency of long droughts lasting 12 months or more. Burke et al. (2006) describe similar findings. The temperature range shown in the diagram is based on best estimates from the combination of Williams et al. and Sheffield and Wood, establishing low and high ends of the range (2.6-3.9°C).
76 Merritt et al.( 2006).
77 Lemmen & Warren (2004); Moulton & Cuthbert( 2000).
78 Lemmen et al. (2008); Bruce et al. (2000).
79 Bruce et al. (2003) project challenges to meeting boundary and transboundary water agreements for several river systems in 2050 under an A2 scenario. Cohen et al. (2000) model the effects of warming on the transboundary Columbia River system, and conclude that “Climate change has the potential to increase the level of current conflicts and to create new ones”. By highlighting potential water availability issues in a changing climate in the Okanagan, Poplar, and Red River basins, as well as the Great Lakes basin, Koshida et al. (2005) also suggest that there may be heightened competition for water resources in some basins as a result of warming. Bruce & Haites (2008) also discuss issues meeting transboundary water sharing agreements. In plotting this impact on degrees of change, we use the likely ranges for the A2 scenario for 2050s and 2080s to bookend low and high end of range, but this impact is likely to continue beyond the high end of range.
80 Field et al. (2007).
81 Mortsch et al. (2003); Murdoch et al.(2000).
82 Lemmen & Warren (2004).
83 Murdoch et al.(2000)
© 2013