watervulnerability

level of uncertainty. Though there may be uncertainty
in characterizing resource value, especially when ratings
comprise more than one resource (for example, frogs plus
fish species), descriptions of resource locations generally
have little error. Likewise, assessments of sensitivity, as
we will see in the next section, are composites of both
intrinsic and anthropogenic factors. Schemes to combine
or weigh the factors contain error, relative to how these
factors are expressed in nature. Nevertheless, these
assessment components are likely to be more accurate
than projections of future temperature and snowpack,
especially regarding what will actually occur decades
from now.
On the White River, Gallatin, and Coconino NFs,
changes to snowmelt hydrology were determined to
be the primary hydrologic change affecting selected
resources. In both the White River NF and Coconino
NF assessments, changes to the existing snow line due
to projected temperature increases were anticipated. The
watershed area within zones of predicted snow elevation
change was used to characterize relative exposure
of subwatersheds. The Gallatin NF assessment used
projected changes in snowpack from the CIG (Figure 8).
The Gallatin NF also included assessments of changes to
summer and winter flow (from VIC) in their assessment.
A similar approach was taken on the Shasta-Trinity NF.
The impact of climate change on stream temperatures
and habitat for salmonids was the focus on four
National Forests (Umatilla, Sawtooth, Helena, Shasta-
Trinity). These pilots employed data that looked deeper
12 | ASSESSING THE VULNERABILITY OF WATERSHEDS TO CLIMATE CHANGE
at potential hydrologic changes than other assessments.
The Chequamegon-Nicolet NFs included a salmonid
(brook trout) in their assessment of potential impacts
of stream temperature increases on 16 species of cold,
cool, and warmwater fishes. In addition to stream
temperature, the Sawtooth NF evaluated potential
changes to frequency of flood flows critical to bull trout
habitat condition. This evaluation was possible because
of support from the Rocky Mountain Research Station, a
leader in assessing potential climate change impacts on
aquatic ecosystems.
The Ouachita NF selected aquatic communities as the
resource of concern, and identified increased sediment
production as the most likely adverse effect to that
resource. Changes in precipitation and temperature
from The Nature Conservancy’s Climate Wizard (see
Table 2) were captured by month from the composite
climate change models. The predicted changes in climate
were then used to modify the climate generator in the
Watershed Erosion Prediction Project (WEPP) Model
(Elliot et al. 1995), which were then used to estimate
sediment production under different climatic scenarios.
The Chequamegon-Nicolet NFs’ assessment considered
how climate change might affect important aquatic
habitats, including lakes and wetlands. A Soil Water
Balance Model was used to assess how potential
groundwater recharge might change in the future
and whether any change will differ by soil type. A
groundwater flow model will eventually be used to
Historic 2040s 2080s
Snowpack Vulnerability
Rainfall Dominant
Transitional
Snowfall Dominant
Change from Historic
Snowmelt Dominant to Transitional
Transitional to Rainfall Dominant
Gallatin National Forest
5th Level HUC
Figure 8. Projected changes in snowpack vulnerability between historic and two future
scenarios, Galatin NF. Data from CIG, using the CIG composite model