Geoscience Reference
In-Depth Information
the smaller volume of warm water involved. In addition,
in contrast to the Norwegian Sea, the shape of the
Alaskan coastline prevents the extension of the drift to
high latitudes (see Figure 7.29).
The Pacific coast ranges greatly restrict the inland
extent of oceanic influences, and hence there is no
extensive maritime temperate climate as in western
Europe. The major climatic features duplicate those of
the coastal mountains of Norway and those of New
Zealand and southern Chile in the belt of southern
westerlies. Topographic factors make the weather and
climate of such areas very variable over short distances,
both vertically and horizontally. A few salient char-
acteristics are selected for consideration here.
There is a regular pattern of rainy windward and drier
lee slopes across the successive northwest to southeast
ranges, with a more general decrease towards the
interior. The Coast Range in British Columbia has mean
annual totals of precipitation exceeding 2500 mm, with
5000 mm in the wettest places, compared with 1250 mm
or less on the summits of the Rockies. Yet even on the
leeward side of Vancouver Island, the average figure at
Victoria is only 700 mm. Analogous to the 'westerlies-
oceanic' regime of northwest Europe, there is a winter
precipitation maximum along the littoral (Estevan
Point in Figure 10.16), which also extends beyond
the Cascades (in Washington) and the Coast Range
(in British Columbia), but summers are drier due to the
strong North Pacific anticyclone. The regime in the
interior of British Columbia is transitional between
that of the coastal region and the distinct summer
maximum of central North America (Calgary), although
at Kamloops in the Thompson valley (annual average
250 mm) there is a slight summer maximum associated
with thunderstorm-type rainfall. In general, the shel-
tered interior valleys receive less than 500 mm per year.
In the driest years certain localities have recorded only
150 mm. Above 1000 m, much of the precipitation falls
Figure 10.16
Precipitation graphs for stations in western Canada. The shaded portions represent snowfall, expressed as water
equivalent.
