watervulnerability

White River National Forest Watershed Vulnerability Assessment, Rocky Mountain Region (R2)
glaciation (0.75), south aspect (0.50), hydroclimatic regime (1.0), weighted precipitation (1.0), extent of
surface water features (1.0), extent of pine beetle mortality (0.5), water uses (1.0), development/roads
(0.5), and the extent of beetle salvage (0.5).
Determination of a Summary Numeric Ranking for Each Subwatershed
At this point, the seven natural and three anthropogenic attributes that could either add to or buffer the
expected climate change effects have been identified. These factors have also been categorized as having
a high, moderate, or low influence and they have been weighted based on the relative strength of their
influence. See the summary in Table 1 below.
In order to aggregate these factors into a single rating, a simple numeric scheme was used. Factors
exerting a high influence were assigned a value of 5, medium a value of 3, and low a value of 1. The
score for each attribute was multiplied by the weighting factor, and those products were averaged for all
attributes within a subwatershed.
Once the average score was calculated for all the subwatersheds, they could easily be partitioned into
groups based on their numeric ‘vulnerability.’ Again, given that no actual physical/biological thresholds
exist based on the numbering scheme used, quartiles served as a consistent and systematic way to
categorize subwatersheds with high, moderate, and low risk of impacts from climate change. Of all the
166 subwatersheds evaluated, the 25% with the highest overall scores were ranked as high vulnerability.
The 25% with the lowest overall scores were ranked as low vulnerability. The middle 50% were ranked as
moderate vulnerability.
Subwatershed Attribute Name Type of Attribute
Relative
Weight
Net Effect Relative to
Climate Change
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 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 1. Summary of attribute types affecting subwatershed resiliency to climate change
Presentation of Results
Recall that the subwatershed attributes were rated based on their effect on one of the resource values
(Aquatic Habitat, Water Uses, or Infrastructure/roads). Consequently, the previously described steps had
to be repeated for each resource value. The results are graphically shown in Figures 7 through 9.
Note that the presence or absence of the resource value did not play a role in the numeric ranking and
categorization. Rather, the subwatershed’s vulnerability was assessed based on the natural and
anthropogenic attributes, then the known resource value occurrences were overlaid on top of those
ratings. In this case, the mapped elements included Colorado River cutthroat trout and boreal toad
populations for the Aquatic Habitat resource value, points of diversion for Water Uses resource value, and
road-stream crossing locations for the Infrastructure/Roads resource value. Therefore, areas of initial
concern for managers would be those subwatersheds with high vulnerability AND a high concentration of
the resource value.
123 Assessing the Vulnerability of Watersheds to Climate Change