Download Mountain Snowpack in Western North America

Mountain Snowpack in Western North America:
locations, characteristics, and changes over the
20th and 21st century with global warming
Jane X and John Y
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Introduction
Global change has many implications throughout our world. One such implication is global
warming due to anthropogenic causes, such as carbon dioxide (CO2) emissions from the
burning of fossil fuels and deforestation; (figure 1). An impact of global warming is the
reduction of mountain snowpack throughout the world’s mountains. While global warming is
affecting mountain snowpack worldwide, this paper will focus on the changes in snowpack in
western North American mountains, more specifically in the mountain ranges of the Cascades,
Rockies, and Sierra Nevada’s of the Western United States, from the 1900’s through the 21st
century. Not only will this paper describe why the snowpack is important, but it will also detail
implications of decreased snowpack on our environment and society.
Figure 1: Carbon Dioxide Variations in the Earth’s atmosphere over the last 400,000 years. Source: Climate Change Resource
Center, www.fs.fed.us/.../figures/primer/-figure3.gif
Snowpack, winter precipitation and water resources
Snowpack is defined as an area of naturally formed, packed snow that usually melts
during the warmer months, (yahoo.com). Snowpack in the western United States is influenced
by the elevation of the mountain ranges, westerly trade winds, and by the El Nino/Southern
Oscillation, (ENSO) event. ENSO is an atmospheric process that can greatly influence global
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weather, (Rohli, Vega 2008). In the United States, during an El Nino phase, the normal track of
the polar front jet stream is altered, and the jet stream may even split into two distinct
branches; a north branch and a south branch, (Rohli, Vega 2008). This altered path of the jet
stream often brings more precipitation into the southern and central regions of the United
States, increasing snowpack in the Rocky Mountains, while at the same time reducing the
amount of precipitation in the Pacific Northwest, thus impacting the snowpack of the Cascade
Range. Figure 2 below illustrates the difference in the path of the North American Westerly
trade winds that occur during an El Nino event and a La Nina event. A La Nina event is a more
intense variation of normal climatic conditions.
.
Figure 2: El Nino and La Nina Conditions over North America
Source: Climate Change Resource Center, www.fs.fed.us/.../figures/primer/-figure3.gif
In much of the west, up to 70% of the annual precipitation falls during the winter,
(Guido, 2008). This winter precipitation, especially that falling as snow, is crucial to the west, as
two of the west’s main sources of water are reliant upon snow melt, the west’s rivers and its
groundwater. For example, Arizona is heavily reliant upon the Colorado River, relying upon the
waters of the river to meet up to 70% of the state’s annual water needs. The Colorado River, in
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turn, is reliant upon the snow fall in the Rocky Mountains, (Guido, 2008). However, Arizona is
not the only state which relies on the Colorado River. In fact the Colorado River Basin, which is
extremely dry and hot, averaging only around four inches of rain per year with an evaporation
rate of 87%, provides water to 25 million people as of 2005. Between 70-80% of the flow of the
Colorado River is from snow melt in the upper elevations of the basin, (Saunders and Maxwell,
2005). Figure 3, below depicts the Colorado River Basin.
Figure 3: Map of Colorado River Basin
Source: Water and Encyclopedia, Science and Issues at www.waterencyclopedia.com/images/wsci_o1_ing
Although the rivers of the west have been developed, through the construction of dams
and reservoirs, in order to maximize the year round use of available water, the greatest water
reservoir in the west is snow. Snow holds water in a semi-frozen state until the water is
released during periods of warmer weather, historically corresponding to the increased need of
water by humans and the environment.
Humans have a greater need for water during the spring and summer months in the
west due to increased requirements for irrigation of lawns, gardens, and irrigated agriculture.
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This increased demand has, in the past, typically corresponded with the available water from
melted winter snowpack. The ecosystem is also reliant upon the spring and summer water from
melted snowpack for a variety of reasons, two of which are listed here. One reason is that
spring and summer melt water provides a critical lifeline for plants and animals during some of
the hottest and driest months of the year which occur between winter and summer
precipitation in many states. Another reason is that many plants and animals of the region have
evolved with the timing of the spring snowpack melt and their budding, reproduction, and
interaction cycles are dependent upon the melt, (Guido, 2008).
Climate change and impacts on western mountain snowpack
Global temperatures are expected to increase between three and ten degrees
Fahrenheit by the end of the 21st century. Temperatures in the western United States are
expected to increase even more than the global average projection with more heating
occurring at higher elevations and during the winter months, (Saunders and Maxwell, 2005).
For example, the higher elevations of the Northern Rocky Mountains have experienced an
increase in temperature three times that of the global average over the last century, (Farge,
2008). With the warming of global temperatures, due largely to anthropogenic causes, less
precipitation is and will be falling as snow, and more is and will be falling as rain throughout the
mountain ranges of the Western United States. This is especially evident in the Cascade
Mountains of the Pacific Northwest where there has been an observed decrease in winter
snowpack of 35% within the last 50+ years, (American Meteorological Society, 2005). This
change in precipitation patterns affects the amount of water that is stored as snow for late
Spring, and early summer release as melt water.
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Figure 4: Changes in April 1 snow water equivalent in the Western United States. Linear trends in April 1 snow water equivalent
(SWE) relative to 1950 at 798 snow course locations in the Western United States and Canada for the period 1950-1997.
Negative trends are shown by red circles and positive by blue circles. SWE is a common measurement for the amount of water
contained in snowpack if it were melted instantaneously. Source: Climate Change Resource Center,
www.fs.fed.us/.../figures/primer/-figure3.gif
Warming temperatures have also caused the snowpack that does form to melt earlier in
the year. In the last 50 years the dates of peak snowmelt runoff have shifted earlier in the year
from 10-40 days, (American Meteorological society, 2005). Increased temperatures which are
reducing snowpack, and causing earlier snowpack melting, is detrimental to both humans and
the natural environment.
As mentioned previously, the majority of the rivers in the west have been largely
developed, through the construction of dams and reservoirs. The development of the rivers
provides humans with the ability to utilize the rivers’ water year round, control floods, and to
provide hydro-electrical power to the growing cities of the west. Earlier snowpack melting may
cause reservoirs to fill prior to an increased need downstream by humans for the water. If the
early melting of snow occurs when reservoirs are already filled to capacity two things could
happen. First, flooding could occur which could cause significant damage to riparian areas and
human infrastructure. Second, untimely releases of water from the reservoirs could have
detrimental effects upon water availability throughout the region during summer months and
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even severely impact the amount of water in reserve for future drought conditions, (Guido,
2008).
Decrease in snowpack also has detrimental consequences for humans throughout the
region as less water is available to store in man-made reservoirs for either summer use, or as a
precaution against drought conditions. Decrease snowpack also means that less water is
available for release from the dams for the production of hydroelectricity. Figure 5 below
depicts the average flow of run-off from snow melt for the Colorado River from 1980-2006. As
less water is available to communities that largely depend from snow run-off, water managers
will face difficult decisions regarding water supplies.
Figure 5: Colorado River Flow
Perhaps more important than the effects on humans of decreased snowpack and earlier
snow melt, is the effect the two have on the environment. Plants and animals rely on snowmelt
to provide water in the spring for reproduction purposes, and also during the summer, when
temperatures are at their highest, and the rains have not yet come. Lack of available water
during spring and summer stresses the ecosystems and increases the risk of insect infestations,
wildfire, and the loss of biodiversity, (Guido, 2008).
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In the Columbia River Basin, which is often thought of as a wet area, is very dry in the
summer. The basin, which is consists of both the Columbia and Snake Rivers and their
tributaries, relies on the upper-basin snowmelt from the Cascade Mountains to provide
summer flow, (Slaughter, Reading). Changes in the amount and timing of the river flow through
the basin may have severe consequences on an ongoing, multi-billion dollar attempt to restore
the endangered salmon population, (Saunders and Maxwell, 2005). Figure 6 below shows the
area covered by the Columbia River Basin.
Figure 6: Map of the Columbia River Basin
According to research that has been conducted by various researchers of the Western
Mountain Initiative, major fire years and insect outbreaks are associated with drought
conditions. The Western Mountain Initiative (WMI) is a collaboration of scientists whose
research focuses on understanding and predicting responses of western mountain ecosystems
to climatic variability and change. In 2006 it was observed that drought conditions in the Rocky
Mountains and in the Eastern Cascades were responsible for insect outbreaks which have
raised the concerned about forest dieback and forest fires. As of 2006 drought was already
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responsible for forest dieback in parts of the Southern Rocky Mountains as well as parts of the
Sierra Nevada’s, (Stephenson et al, 2006).
Figure 7: Important Rivers and Mountain Ranges in California
Another result of decreased snowfall and snow accumulation due to warming
temperatures is the changing elevation of the tree line. As snowpack levels decrease and
temperatures increase, higher elevations become great habitat for tree species that would
otherwise be found at lower elevations. Change in forest composition will cause a change in
other plant and animal species at that particular elevation. As warming continues, the higher
elevation ecosystems are in jeopardy of becoming extinct, and species composition will be
greatly altered at these elevations, (Stephenson et al, 2006).
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Snowpack in the mountains of the western United States has been decreasing for the
last few decades and is expected to continue into and through the 21st century. Scientists
believe that the changes that have already occurred are mild compared to the changes that
may occur if carbon dioxide emissions continue to increase. The following are a few examples
of Western climate projections from scientific studies, (Stephenson et al, 2006):
Colorado River basin: losses of 24% of the basin’s snowpack are predicted by 2010-2039 and
30% by 2040-2069.
Columbia River basin: losses of 35% of the basin’s snowpack are predicted by 2050 and 47% by
2090.
Milder winter Cascade Mountains: the predicted losses are nearly 60% by
2050 and 72% by 2090.
California: losses of 29 to 89% of the state’s snowpack are predicted by 2070-2099
Summary
Global change, in the form of global warming due to anthropogenic causes, is
responsible for the decrease in snowpack in the mountains of the western United States and
around the world. This paper has not only attempted to describe the importance of mountain
snowpack in the west in regards to both the ecosystem and to humans, but has also attempted
to describe consequences of reduced mountain snowpack for the western United States. While
many changes in ecosystem ecology and water management have already begun to show up
due to warming temperatures throughout the region, scientific studies are pointing to more
pronounced changes for the future, if carbon emissions continue to increase global and
regional temperatures.
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Works Cited
Atkins, William Arthur. "Water and Encyclopedia: Science and Issues." Water and Encyclopedia:
Science and Issues. Water Encyclopedia, 2010. Web. 12 Apr. 2010.
<www.waterencyclopedia.com/images/wsci_01.ing>.
Climate Change in Mountain Ecosystems. Ed. Daniel Farge. US Dept of the Interior, USGS, 24
July 2008. Web. 28 Mar. 2010. <http://nrmsc.usgs.gov/research/global.htm>.
Declining Mountain Snowpack in Western North America: Implications for Water Resource
Management in the Western U.S. Proc. of Environmental Science Series (ESSS), Dirksen
Senate Office Bldg, Room G-50. American Meteorological Society, 25 Aug. 2009. Web.
01 Apr. 2010. <http://www.ametsoc.org/atmospolicy/50526ESSS.html>.
Francis, Paul. "Las Vegas Ranked #4 by Businessweek as Most Desirable City to Move To." Las
Vegas Living Condictions. Las Vegas Real Estate For You, 06 Jan. 2009. Web. 13 Apr.
2010. <lasvegasrealestate4u.files.wordpress.com/12008>.
Guido, Zack. "Mountain Snowpack in the West and Southwes." Mountain Snowpack in the West
and Southwest. The University of Arizona, Board of Regents, 2009. Web. 01 Apr. 2010.
<http://www.southwestclimatechange.org/impacts/water/snowpack>.
Houghton Mifflin. Web. 01 Apr. 2010.
<http://education.yahoo.com/reference/dictionary/entry/SNOWPACK>.
The Natural Climate System. Publication. United States Forest Service, Climate Change Resource
Center. Web. 12 Apr. 2010. <www.fs.fed.is/.../figures/primer/gig3.gif>.
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Rohli, Robert V., and Anthony J. Vega. Climatology. 1st ed. Sudbury, Mass.: Jones and Bartlett,
2008. 73-78. Print.
Saunders, Stephen, and Maureen Maxwell. Less Snow, Less Water:Climate Disruption in the
West. Rep. The Rocky Mountain Climate Organization, Sept. 2005. Web. 01 Apr. 2010.
<http://www.rockymountainclimate.org/website%20pictures/Less%20Snow%20Less%2
0Water.pdf>.
Slaughter, Richard, and Don Reading. "Snake River Case Study: Institutions, Adaptaions, the
Prior Appropriation Doctorine, and the Development of Water Markets." Snake River
Case Study: Institutions, Adaptaions, the Prior Appropriation Doctorine, and the
Development of Water Markets. University of Washington, Climate Impacts Group, Joint
Institute for the Study of Atmospher and Ocean. Web. 12 Apr. 2010.
<cses.washington.edu/cig/figures/crbtopo1_BIG.gis>.
Stephenson, Nate, Dave Peterson, Dan Farge, Craig Allen, Don McKenzie, Jill Baron, and Kelly
O'Brian. Rep. Response of Western Mountain Ecosystems to Climatic Variability. The
Western Mountain Initive. Web. 30 Mar. 2010.
<http://www.fs.fed.us/psw/cirmount/wkgrps/ecosys_resp/postings/pdf/WMI_Park%20
Science_2006.pdf>.
Web. <http://gc.energy.gov/NEPA/nepa_documents/EIS/eis-0232/html/scans/f3-1.gif>.
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