WATER DEMAND
(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.
