It is axiomatic
that water defines a river, but it is particularly so for the Columbia River,
where the unique geography and climate of the river basin contribute to the
tremendous volume of annual runoff — fourth-largest in North America behind
Mississippi, Mackenzie, and St. Lawrence. Historic precipitation patterns
influence ecological processes such as the location and abundance of fish and
wildlife populations, human uses of the land, and regimes of fire and flood.
climate west of the Cascade Mountains is influenced by the proximity of the
Pacific Ocean. Winters are mild, and rainfall is frequent and at times heavy.
Snowfall is rare west of the Cascades except at the higher elevations of those
mountains and in the Coast Range. In the low-lying areas of the Columbia and
Willamette river valleys snow usually only occurs within a period of weeks in
January and February. The climate east of the Cascades is markedly different, a
continental climate of cold, snowy winters and warm, dry summers. The
continental climate extends into British Columbia, where successive mountain
ranges also catch winter storms and snowfall is frequent and heavy, but summers
generally are warm and dry.
precipitation varies from 45 inches in the Portland/Vancouver metropolitan
area, to 100 inches or more in the heart of the
Columbia River Gorge,
to fewer than 8 inches in the rain shadow area immediately east of the
Cascades. Most of the interior Columbia River Basin receives between 12 and
about 30 inches of precipitation annually, with the exception of the Snake
River Plain in southern Idaho, which is drier.
mountain ranges within the Columbia River Basin typically receive 100 to 200
inches of snow annually; this is one reason for the Columbia’s huge annual
runoff volume, which averages 192 million acre-feet. The annual spring freshet,
when the snow melts and runoff peaks in the spring and early summer,
historically provided the transit to the estuary and ocean for juvenile salmon
and steelhead. Dams altered this flow regime by catching and holding
water in reservoirs for winter power generation, thus reducing the volume and
velocity of the spring flow.
also affects growing seasons in the Columbia River Basin. At higher elevations,
the season can last as few as 30 days. In the intermontane valleys and
plateaus, however, such as the interior plateau that stretches mostly unbroken
from central Washington to central Oregon, and in the comparatively damp
Willamette Valley of Oregon, growing seasons are 150 to 200 days long.
quality in the Columbia Basin is heavily affected by wind, and the interior
parts of the basin can be very windy. The average wind speed in the Columbia
River Gorge, where the steep walls can act as a funnel, is 10 miles per hour.
This is primarily why the Gorge has become so popular with wind surfers.
Frequent and sustained winds of 20 miles per hour or faster are common. Farther
to the east, in central and southeastern Washington and northern and
northeastern Oregon, the fine-grained loessal soils are particularly
susceptible to wind erosion, and periodic dust storms in the spring and summer
can raise clouds of roiling dust that halt traffic on the inland highways. It
is not unusual for eastern Washington to be blanketed with dust from spring and
summer winds from the west. The frequency of sustained winds has prompted a
renaissance of wind-power developments in southeastern Washington and
northeastern Oregon. Long rows of 100 or more spinning turbines are becoming an
increasingly common sight on the mostly treeless ridgetops.
the Gorge funnels wind, hot in summer and cold in winter, into the
Portland/Vancouver area, the largest population center in the Columbia River
Basin, with dramatic effects. In summer, the hot wind can blow temperatures to
over 100 degrees F and cause a marked drop in humidity in the Portland area.
The winds continue down the river all the way to Astoria, where the temperature
might climb into the 80s or 90s. Yet just a few miles south of Astoria, where
the river wind doesn’t reach, it will be 30 degrees cooler and foggy. In
winter, cold winds blowing down the Gorge can chill the Portland area to well
below freezing. When a warm, wet weather system overrides the surface-level
cold air, the temperature difference between the surface and about 2,000 feet
in elevation can be 15 or 20 degrees — enough to keep the inevitable rain from
turning to snow before it hits the ground. These storms can be vicious, dumping
up to 10 feet of snow in the western end of the Gorge, although that has not
happened since the early 20th century, but more commonly laying down
a coating of solid ice. Such a storm paralyzed the Portland area for four days
in January 2004.
Climate change impacts and the Columbia River Basin
A significant proportion of scientific opinion, based on both empirical data
and large-scale climate modeling, holds that the Earth is warming due to
atmospheric accumulation of carbon dioxide (CO2), methane, nitrous oxide, and
other greenhouse gasses. The increasing atmospheric concentration of these
gasses appears to be largely from human activities, in particular, the burning
of fossil fuels. The effects of warming may include changes in atmospheric
temperatures, storm frequency and intensity, ocean temperature and circulation,
and the seasonal pattern and amount of precipitation. Possible beneficial
aspects to warming, such as improved agricultural productivity in cold climates,
on balance appear to be outweighed by adverse effects such as increased
frequency of extreme weather events, flooding of low-lying coastal areas,
ecosystem stress and displacement, increased frequency and severity of forest
fires, and northward migration of warm-climate diseases. While there is general
agreement on the fact and impacts of global warming, significant uncertainties
remain regarding the rates and ultimate magnitude of warming and its effects.
In its Fifth Northwest Power
Plan, the Council addresses potential impacts of climate change. Two
appendices, Appendix M and Appendix N, address global climate change policy and
effects of global climate change on the Columbia River Basin hydroelectric
system, respectively. Global models seem to agree that Northwest temperatures
will be higher, but they disagree regarding levels of precipitation. Current
thinking by Northwest scientists leans toward a warmer and wetter climate. The
proportion of winter precipitation currently falling as high-elevation snow is
expected to decline, and peak runoff is expected to shift from springtime to
winter. Summer stream flows would decline as a result of loss of snow pack.
Warming would lead to a relative reduction in winter peak electricity demand and
an increase in the frequency and intensity of summer peaks.