watervulnerability

sensitivity. Most were derived from the Watershed
Condition Classification (Figure 12). The Gallatin NF
characterization of sensitivity had two components:
one included intrinsic watershed attributes, the other
included levels of disturbance. The Watershed Condition
Classification ratings of “functioning,” “functioning at
risk,” and “non-functioning” were used to characterize
disturbance. Since National Forests and Grasslands now
have completed the Watershed Condition Classification,
this data would be useful in conducting future WVAs.
Pilot Forests that took advantage of existing condition
ratings tended to apply them to all resource issues. Several
pilot Forests, however, identified different indicators for
each resource value. While many indicators are important
influences on multiple water resources, some are not.
For instance, the most important factors affecting peak
flows and infrastructure may differ from those that most
influence springs and other aquatic habitats.
Pilot Forests took several approaches to developing
ratings of watershed sensitivity. In the simplest
applications (Ouachita and Chequamegon-Nicolet
NFs), sensitivity indicators (e.g., basin slope, peat land
type) were used to place watersheds into different
categories. Other pilot Forests produced sensitivity
ratings based on numerous indicators. When multiple
indicators were used, pilot Forests developed methods
of weighting and rating the relative influence of the
attributes. For example, when considering influences
on stream habitat, the amount of water withdrawn
from a subwatershed is likely more important than the
condition of terrestrial vegetation, and would therefore
be given greater weight in calculating a sensitivity score.
One approach to weighting sensitivity indicators, from
Subwatershed Attribute Type of Attribute Relative Weight
Geochemistry of parent geology Inherent to watershed 0.25 Buffer
Extent of glaciation Inherent to watershed 0.75 Buffer
Aspect Inherent to watershed 0.50 Additive
Hydroclimatic regime Inherent to watershed 1.0 Additive
Weighted precipitation Inherent to watershed 1.0 Buffer
Extent of surface water features Inherent to watershed 1.0 Buffer
Extent of large-scale pine beetle
mortality
16 | ASSESSING THE VULNERABILITY OF WATERSHEDS TO CLIMATE CHANGE
Sensitivity x Stressors
Risk Ranking Matrix
Stressors
Net Effect Relative to
Climate Change
Inherent to watershed 0.5 Buffer (short term)
Water uses Anthropogenic 1.0 Additive
Development (primarily roads) Anthropogenic 0.5 Additive
Extent of beetle salvage Anthropogenic 0.5 Additive (short term)
Table 6. Summary of attribute types affecting subwatershed resilience to climate change (White River NF)
Sensitivity
Low
Moderate
High
Low Moderate
Low
Low
High
High
Low Low
Low
High
High
High
Figure 13. Scheme used to rate watershed sensitivity
on the GMUG NFs. The matrix combines ratings for
water shed stressors and sensitivity. Ratings of erosion
sensitivity (6 elements) and runoff sensitivity (7 elements)
were combined to produce the sensitivity rating. Stressor
rating was derived by combining ratings of past management
(2 elements), roads (3 elements), vegetation treatments,
private land, and mining.
the White River NF assessment, is shown in Table 6. In
several cases, pilot Forests distinguished intrinsic and
anthropogenic factors, and used a categorical matrix
Figure 14. Bayesian belief network for determining overall
physical condition, from the Sawtooth NF WVA. Contri buting
factors included habitat access, flow, channel condition, habitat
elements, water quality, and watershed conditions.