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Long-Duration Drought Variability and Impacts on Ecosystem Services: A Case Study from Glacier National Park, Montana

Glacier National Park, Montana USA.  Photo by Greg Pederson. 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
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.
Download data from the WDC Paleo archive:
Glacier National Park Drought Reconstruction

Figure 4. (B) Mean centered reconstructed MSD (blue line) smoothed with a 10 yr cubic spline (thick red line) and spanning A.D. 1540-2000. Gray lines represent ± 1 sigma, and light blue and dark red line represent ± 2 sigma respectively from the long-term mean. (C) Decadal-scale drought regimes exhibiting the significant step-changes in the mean (event intensity) identified by the intervention model.
Figure 4. The summer drought reconstruction for Glacier NP.
To read or view the full study, please visit the AMS website.
It was published in Earth Interactions, Volume 10, Paper 4, January 2006.
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