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Long-Duration Drought Variability and Impacts on Ecosystem Services: A Case
Study from Glacier National Park, Montana
Earth Interactions
Volume 10, Paper 4, January 2006.
Gregory T. Pederson1,2, Stephen T. Gray3,
Daniel B. Fagre2, and Lisa J. Graumlich1
1 Big Sky Institute, Montana State University, Bozeman, Montana
2U.S. Geological Survey, Glacier Field Station, W. Glacier, Montana
3U.S. Geological Survey, Desert Laboratory, Tucson, Arizona
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ABSTRACT:
Instrumental climate records suggest that summer precipitation and winter snowpack in
Glacier National Park (Glacier NP), Montana, vary significantly over decadal to
multidecadal time scales. Because instrumental records for the region are limited
to the twentieth century, knowledge of the range of variability associated with
these moisture anomalies and their impacts on ecosystems and physical processes are
limited. The authors developed a reconstruction of summer (June-August) moisture
variability spanning A.D. 1540-2000 from a multispecies network of tree-ring
chronologies in Glacier NP. Decadal-scale drought and pluvial regimes were
defined as any event lasting 10 yr or greater, and the significance of each
potential regime was assessed using intervention analysis. Intervention analysis
prevents single intervening years of average or opposing moisture conditions
from ending what was otherwise a sustained moisture regime. The reconstruction
shows numerous decadal-scale shifts between persistent drought and wet events
prior to the instrumental period (before A.D. 1900). Notable wet events include
a series of three long-duration, high-magnitude pluvial regimes spanning the end
of the Little Ice Age (A.D. 1770-1840). Though the late-nineteenth century was
marked by a series of >10 yr droughts, the single most severe dry event occurred
in the early-twentieth century (A.D. 1917-41). These decadal-scale dry and wet
events, in conjunction with periods of high and low snowpack, have served as a
driver of ecosystem processes such as forest fires and glacial dynamics in the
Glacier NP region.
Using a suite of paleoproxy reconstructions and information from previous studies
examining the relationship between climate variability and natural processes,
the authors explore how such persistent moisture anomalies affect the delivery
of vital goods and services provided by Glacier NP and surrounding areas.
These analyses show that regional water resources and tourism are particularly
vulnerable to persistent moisture anomalies in the Glacier NP area.
Many of these same decadal-scale wet and dry events were also seen among a
wider network of hydroclimatic reconstructions along a north-south transect
of the Rocky Mountains. Such natural climate variability can, in turn, have
enormous impacts on the sustainable provision of natural resources over wide
areas. Overall, these results highlight the susceptibility of goods and
services provided by protected areas like Glacier NP to natural climate
variability, and show that this susceptibility will likely be compounded
by the effects of future human-induced climate change.
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