Impacts of snow-cover changes on hydroelectric power, particularly in the American West,
human economies and well-being Canada, and Europe
81,82
. The declining springtime snow
cover in the Pacific Northwest of the United States and
Impacts on water resources rising snowlines projected for many mountain areas,
noted in the ‘Trends and outlook’ section above, threaten
One of the most dramatic impacts of changing snow these critical water supplies.
cover is on water resources. Snow cover in mountain
regions provides critical water supplies, serving nearly Mountain snow cover typically develops in the autumn
one-sixth of the global population with freshwater for and grows to a maximum depth in early spring (Figure
domestic, agricultural and industrial uses
79
. Much of the 4.11). As day length and sun angles increase, so do air tem-
arid American West
79
and Central Asia
80
(Figure 4.10) peratures, causing snow cover to warm and begin to melt.
depends heavily (about 75–85 per cent) on snow melt to Snow cover balances the availability of water in mountain
supply water for municipalities and agriculture. Snow environments. Where winter precipitation falls as rain,
melt driven water resources are crucial for generation of surface runoff occurs almost immediately. In contrast,
(a) (b)
Figure 4.10: Snow cover provides critical water supplies used for many purposes.
(a) Melting of prairie snow cover, seen here in Saskatchewan, Canada, provides spring ponds that are essential for recharge of
groundwater and soilwater, for farm water supplies and as spring wetlands for waterfowl migrations through what is otherwise a
semi-arid environment.
(b) Melting of alpine snow cover forms a small stream in the Rocky Mountains in British Columbia, Canada. This segment of the
Rocky Mountains contains the headwaters of the Columbia River, which supplies water to a large area of western Canada and north-
western United States including many important irrigation and hydroelectric generation projects.
Photos: J. Pomeroy
CHAPTER 4 SNOW 53