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Executive Summary
In
the American West, no other effect of climate disruption is as
significant as how it endangers the region’s already scarce snowpacks
and water supply. With the inherent vulnerability of the dry West to
even small changes in the snow-water cycle, these risks alone present
ample reason for Westerners to take action to protect this special
region.
The Likely Effects of Climate Disruption on the West’s Water
Scientists believe that climate disruption in the West likely will
result in more heat, less snowpack, and earlier snowmelt and runoff.
This may be accompanied by other adverse effects, including increased
intensity, frequency, and duration of drought.
■
More heat. Temperature increases in the West are likely to be even
greater than the projected 3° to 10°F worldwide increase by the end of
the 21st Century, compared to 1990. The heating is likely to be greater
in the winter than in the summer and at higher elevations than in
lowlands, with significant implications for snowpacks and water
availability.
■
Smaller snowpacks. It is very likely that more winter precipitation
will fall as rain instead of snow, periods of snowpack accumulation
will be shorter, and snowpacks will be smaller.
■
Earlier snowmelt. Warming earlier in the year very likely will melt
snowpacks sooner. Peak water flows would occur that much sooner than
the summertime peak water needs of cities, farmers and ranchers, and
others.
■
More evaporation and dryness. Higher temperatures would increase
evaporation from streams and reservoirs, soil dryness, and the needs of
crops and other plants for supplemental water.
■
More flood-control releases. Warming in the mountains in late winter
and early spring very likely will increase snowmelt and river flows
then, and reduce them later in the year. The risk of flooding likely
will increase, and water managers may be forced to make flood-control
releases more often from reservoirs, leaving less water to be stored
for summertime needs.
■
Less groundwater. Snowpacks also are essential contributors to the
West’s groundwater, so reduced snowpacks could reduce groundwater
supplies, too.
■
More legal restrictions. Environmental constraints, which sometimes now
limit the water available for consumptive use in the West, may be
triggered more often as a result of climate disruption. Changes in
water supplies also may trigger water-use restrictions under interstate
compacts.
■ More droughts. Climate disruption could lead to more intense, frequent, and longer-lasting droughts in the interior West.
More
heat, less snowpack, less available water, and possibly more droughts
are likely to lead to other changes across the West. Most
significantly, wildfires are likely to increase in number and severity.
Climate Disruption Is Under Way In the West
It is now accepted by the scientific community that, worldwide, the
climate is changing as a result of human activities. In the American
West, too, climate disruption is under way.
■
More heat. The United States, along with the rest of the world, has
warmed, with temperature increases in the West greater than in other
regions of the contiguous states.
■ Less snowfall. As the West has warmed, less winter precipitation now is falling as snow and more as rain.
■
Smaller snowpacks. At most snowpack-measurement sites across the West,
snowpack levels have declined over the period 1950 to 2000.
■
Earlier snowmelt. Across the West, springtime peak streamflows are
earlier than 50 years ago. In many cases, the peak snowmelt advanced by
10 to 30 days.
■
More wildfires. Wildfire in the West has increased, particularly in the
last two decades. Researchers have identified climate factors as being
a significant contribution to this trend.
New Findings
For
this report, the Rocky Mountain Climate Organization (RMCO) conducted a
new analysis of government temperature and snowpack records for the
upper basins of the Columbia River, Missouri River, Colorado River, and
Rio Grande for evidence of human-caused climate change.
■
Increased temperatures. In each river basin, the most recent five-year
period was the hottest in the past 110 years. In the upper Columbia
River basin, 2000-2004 was 1.5°F hotter than the historic average; in
the upper Missouri basin, 1.5°F hotter; in the upper Colorado basin,
2.1°F hotter; and in the upper Rio Grande, 2.5°F hotter. These
temperature increases coincided with and worsened the effects of the
recent West-wide drought, by increasing evaporation rates from streams
and reservoirs, soil dryness, and the water needs of crops and other
plants.
■
Greatest warming in winter and spring. In all four basins, the monthly
pattern of the warming that occurred in 1995 through 2004 reveals what
could be regarded as a signature of climate disruption: The warming has
been greatest in January, February, and March. This timing is
consistent with predictions that warming resulting from climate
disruption will be greatest in winter and spring. Also, this is when
warming has the greatest effects on the size of snowpacks and the
timing of snowmelt.
■
Reduced snowpacks. At government snowpack-measurement sites with
records going back to 1961, from 1990 on snowpack levels have been
below average for 13 of the last 16 years in the Columbia River basin,
11 of 16 years in the Colorado River basin, 14 of 16 years in the
Missouri River basin, and 10 of 16 years in the Rio Grande basin.
In
sum, the RMCO analysis offers further evidence that climate disruption
is already under way in the West in ways that jeopardize the region’s
snow and water resources.
Projections of Future Changes
Scientists believe that the changes in climate observed so far are just
a mild foretaste of what is likely to come if global-warming emissions
continue to increase. A few illustrative examples of climate
projections for the West from recent scientific studies include:
• For the Colorado River basin, losses of 24% of the basin’s snowpack are predicted by 2010-2039 and 30% by 2040-2069.
•
For the Columbia River basin, losses of 35% of the basin’s snowpack are
predicted by 2050 and 47% by 2090. For the milderwinter Cascade
Mountains, the predicted losses are nearly 60% by 2050 and 72% by 2090.
• For California, losses of 29 to 89% of the state’s snowpack are predicted by 2070-2099.
Changing the Odds
With all that the West has at risk, the region has good reason not only
to do its share to deal with climate disruption, but also to be a
leader in showing the rest of the nation and world what can be done.
Encouragingly, there are growing signs of new western leadership and
action in addressing climate disruption. Much more needs to be done,
but these first steps suggest that Westerners are beginning to choose a
new path to keep the region such a special place.
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