Understanding the vulnerability of Canada's water resources to climate change is vitally important. Water is one of Canada's greatest resources. We depend on the availability of a clean, abundant water supply for domestic use; food, energy and industrial production; transportation and recreation; and the maintenance of natural ecosystems. It is estimated that water's measurable contribution to the Canadian economy reaches $7.5 to 23 billion per year.⁽¹⁾

Canada has a relative abundance of water, possessing 9% of the world's renewable freshwater, yet only 0.5% of the global population.(2) However, the water is not evenly distributed across the country, and water availability varies both between years and with the changing seasons. As a result, most regions of the country have experienced water-related problems, such as shortages (droughts), excesses (floods) and associated water quality issues. For example, the drought of 2001 affected Canada from coast to coast (Table 1), with significant economic and social impacts. In the 1990s, severe flooding in the Saguenay region of Quebec (1996) and Manitoba's Red River valley (1997) were two of the costliest natural disasters in Canadian history.

Table 1: The 2001 drought across Canada ⁽³⁾

In its Third Assessment Report, the Intergovernmental Panel on Climate Change projects an increase in globally averaged surface air temperatures of 1.4-5.8°C by 2100. Changes of this magnitude would significantly impact water resources in Canada.⁽⁴⁾ Climatic variables, such as temperature and precipitation, greatly influence the hydrological cycle, and changes in these variables will affect runoff and evaporation patterns, as well as the amount of water stored in glaciers, snowpacks, lakes, wetlands, soil moisture and groundwater. However, there remains uncertainty as to the magnitude and, in some cases, the direction of these changes. This is related to the difficulty that climate models have in projecting future changes in regional precipitation patterns and extreme events, and to our incomplete understanding of hydroclimatic processes.

In addition to the expected shifts in hydrological parameters, potential changes in the economic, demographic and environmental factors that influence water resources must also be considered. The response of water users, as well as water management mechanisms, to climate change will greatly influence the vulnerability of water resources. Both the ability and the willingness of society to undertake appropriate adaptive measures are critically important.

The impacts of climate change on water resources will vary across the country, due to regional differences in climate changes, hydrological characteristics, water demand and management practices. Some of the major potential impacts are listed in Table 2.

From this table, it is evident that the potential impacts of extreme events, seasonal shifts in flow regimes and reduced winter ice cover are key issues for several regions of Canada.

Table 2: Potential impacts of climate change on water resources (derived from Figure 15-1 in reference 4)

This chapter examines current research on these and other issues, as well as recent progress in adaptation research. Focus is placed on the impacts on water supplies and demand, and on options to adapt to these impacts. Many other aspects of water resources related to transportation, health and fisheries are addressed in other chapters of this report. While significant uncertainty remains in projecting future impacts, it does not limit our ability to take action to reduce our vulnerability to climate change. By understanding the range of possible impacts, as well as the intricate role of societal response to changing conditions, we will be better prepared to reduce losses and capitalize on potential benefits.