watervulnerability

Using Historic Data
One finding consistent to all the pilots was the value
of local historic data in providing local context and
understanding of climate change. Display of historic
changes with strong connection to local water resource
values is typically easier to understand and appreciate
than projections of future conditions. Projections
are uncertain becaues they are associated with future
emission scenarios and modeling assumptions.
Differences between models increase as they are
projected multiple decades into the future and display
high variability that may be unsettling to managers.
Figure 5. Duration of Ice Cover (days) on Lake Mendota
in Wisconsin, 1855-2008
Snow Depth (in) Max, Mean & Min
250
200
150
100
50
0
1945
1955
1965
1975
1985
1995
Klamath Province
Trinity Basin
West side of forest
(22 stations)
2005
2015
8 | ASSESSING THE VULNERABILITY OF WATERSHEDS TO CLIMATE CHANGE
Historic data helps both analysts and decision-makers
by providing local context and trends in climatic
conditions.
Two examples from the pilot assessments are included
here. The first shows changes to ice cover on Lake
Mendota in southern Wisconsin (Figure 5). This
historical trend was obtained from the Wisconsin
Initiative on Climate Change Impacts (WICCI) by
the Chequamegon-Nicolet NF during the assessment
process. The second example shows changes in snow
depth from the Trinity and Sacramento River basins in
the Shasta-Trinity NF (Figure 6).
Climate Change Projections
Evaluation of climate exposure was the most difficult
component of the assessment for several pilot Forests,
due primarily to lack of experience with downscaled
global climate modeling data. There were two basic
challenges: deciding which climate change projections
to use, and selecting the climate metrics.
The availability of downscaled climate model data has
increased substantially since the WVA pilot project was
initiated. Of particular note is data now available from
the Climate Impacts Group (CIG) at the University of
Washington. The CIG has evaluated available Global
Circulation Models (GCMs), and determined which
models and ensembles of models produce the best fit
with historic data, for the major river basins of the
western United States. Data provided by CIG were used
Snow Depth (in) Max, Mean & Min
250
200
150
100
50
0
1920
1930
1940
1950
1960
1970
1980
1990
2000
2010
Southern Cascades
Sacramento Basin
East side of forest
(19 stations)
Figure 6. Changes in average snow depths from snow courses located in the Trinity River basin (1945-
2009) and Sacramento River basin (1930-2009). Blue is the mean, red is the minumum, and green is the
maximum snow depth.)