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(A Canadian Perspective)
"The consequences of climate change for water resources depend not only on possible changes in the resource base (supply)…but also on changes in the demand, both human and environmental, for that resource.”
Future water demand will be affected by many factors, including population growth, wealth and distribution. Globally, it is estimated that between half a billion and almost two billion people are already under high water stress, and this number is expected to increase significantly by 2025, due primarily to population growth and increasing wealth. Warmer temperatures and drier conditions due to climate change would further increase future water demand in many regions.
Where climate change is associated with increased aridity, it would directly affect water demand with respect to agricultural and domestic uses. For example, outdoor domestic water uses (e.g., gardening and lawn watering) and drinking-water demand tend to increase in warmer, drier conditions. In some cases, technological and management changes may sufficiently increase water use efficiency to address the increased demand. Management changes that work to reduce the demand for water will also be important. Warming of surface waters would have a direct impact on industrial operations
by decreasing the efficiency of cooling systems, which could in turn reduce plant outputs.
Another major demand on water resources is hydroelectric power generation, which fulfills approximately two-thirds of Canada’s electricity requirements. Studies suggest that the potential for hydroelectric generation will likely rise in northern regions and decrease in the south, due to projected changes in annual runoff volume. For example, lower water levels are expected to cause reductions in hydro generation in the Great Lakes basins. An increase in annual flows, however, will not always lead to increased hydro production. Increases in storms, floods and sediment loading could all compromise energy generation. In western Canada, changes in precipitation and reduced glacier cover in the mountains will affect downstream summer flows and associated hydroelectric operations. Moreover, changes in the ice regimes of regulated rivers will likely present the hydro industry with both opportunities, in terms of shorter ice seasons, and challenges, from more frequent midwinter break-ups.
The seasonality of the projected changes, with respect to both the availability of and demands for water resources, is another important factor. For example, during the summer months, lower flow levels are projected to reduce hydroelectric generation potential, while more frequent and intense heat waves are expected to increase air-conditioner usage and therefore electricity demand. Demand for hydroelectric power exports is also likely to increase in the summer, due to increased summer cooling needs.
Increased demand in any or all of these sectors would increase the conflict between alternative water uses, including in-stream needs to retain ecosystem sustainability. Improvements in water use efficiency may be required to prevent the extinction of some aquatic species and the degradation of wetlands, rivers, deltas and estuaries.
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