Water resources is one of the highest-priority issues with respect to climate change impacts and adaptation in Canada. A clean and reliable water supply is critical for domestic use, food and energy production, transportation, recreation and maintenance of natural ecosystems. Although Canada possesses a relative abundance of water on a per capita basis, the uneven distribution of water resources and year-to-year variability mean that most regions of the country have experienced water-related problems, such as droughts, floods and associated water quality issues.

Such problems are expected to become more common as a result of climate change. The hydrological cycle is greatly influenced by temperature and precipitation, and even small changes in these parameters can affect water supply through shifts in runoff, evaporation and water storage (e.g., in glaciers, lakes and soil). There are still uncertainties, however, regarding the magnitude, and in some cases the direction, of future changes, in part due to the limitations of climate models. Although impacts would vary on a regional basis, it is apparent that certain aspects, including extreme events, reduced ice cover and shifts in flow regimes, are concerns in many areas of the country. Overall, the most vulnerable regions would be those already under water stress, such as parts of the Prairies and the Okanagan Valley, where demand is already approaching or exceeding supply.

In many regions, decreases in flow volumes and water levels are expected to create or increase water supply problems during the summer months. In Prairie rivers, for example, summer flows are expected to decrease due to reduced water supply from snowmelt and glacier runoff. In fact, data indicate that a long-term trend of declining flows has already begun. Accompanying decreases in shallow groundwater resources could further compound water shortages. Water supply issues are also expected to become a greater concern in the Great Lakes basin, where a range of sectors would be affected by declining water levels (Figure 2). In the winter, however, less ice cover, more rain-on-snow precipitation events and more frequent winter thaws would increase the risk of flooding in many regions of the country.

Figure 2: Water resources is a crosscutting issue larger image [JPEG, 91.2 kb, 800 X 589, notice]

Changes in flow patterns and water levels could also result in decreased water quality. Lower water levels and higher temperatures could increase levels of bacterial, nutrient and metal contamination, while an increase in flooding could increase the flushing of urban and agricultural waste into source water systems. This would cause taste and odour problems and increase the risk of water-borne health effects in communities across the country. Water supplies, recreational activities and natural ecosystems would all be affected. Some regional water quality concerns include saltwater intrusion in coastal areas and the rupture of water infrastructure in the North as a result of permafrost degradation.

As water supplies diminish, at least seasonally, and water quality problems increase, there would be less high-quality water available for human use. At the same time, agricultural, domestic and industrial demands (e.g., irrigation, lawn watering and equipment cooling, respectively), would likely increase in parts of the country that become warmer and drier. As a result, supply-demand mismatches are expected to become more common, and technological, behavioural and management changes would be required to deal with potential conflicts.

Many of the commonly recommended adaptation options to address climate change in the water resources sector, including water conservation and preparedness for extreme events, are based on strategies for dealing with current climate variability. Structural adaptations, such as dams, weirs and drainage canals, tend to increase the flexibility of management operations, although they also incur economic, social and environmental costs. For this reason, upgrading existing infrastructure to better deal with future climates may often be preferable to building new structures. Design decisions should focus primarily on extreme events and system thresholds, rather than on changes in mean conditions.

Demand management is an important institutional and social adaptation, which involves reducing consumer demands for water through mechanisms such as water conservation initiatives and water-costing mechanisms. Community water conservation programs can be very effective at reducing water consumption, while economics, pricing and marketing can help balance water supply and demand.

Climate change should be incorporated into current water management planning. Although widespread inclusion of climate change in water management has yet to be realized, there are regions, such as the Grand River basin in southwestern Ontario, that do consider future climate in their planning activities. To best deal with the uncertainties regarding climatic and hydrological change, managers should consider climate change in the context of risk management and vulnerability assessment.