watervulnerability

Shasta Trinity National Forest Watershed Vulnerability Assessment, Pacific Southwest Region (R5)
Figure 16. Ranking of watershed sensitivity based on snow dominated runoff processes. Higher numerical scores
represent higher percentage of the watershed with snow.
Combining Values, Exposure (Stressor) and Sensitivity
A rating of each element (resource value, exposure, and sensitivity) was derived for each watershed, and
these scores divided into fifths to obtain relative ratings of 1-5, based solely on values on the Shasta
Trinity National Forest. They do not represent ecological thresholds. A “one” represents the lowest value
(or stressor). A “five” corresponds to the highest value (or stressor).
Each of the ratings is the combination of several elements. For example, the aquatic features resource
combined information on both springs and lakes (see Table 3). The scores were then added together using
the weighted average approach from the WVA (USDA 2011) to obtain a total “resource value” score, a
total “exposure” score and a total sensitivity score.
The process of combining two data sets into one combined ranking is displayed by using both Table 3 and
Figure 17. For example, the final “value score” in Table 3 (6 th column from the left) is multiplied by 10.
Refer next to the matrix (Figure 17) to find the intersection of this “resource value” score (10 to 50) and
the corresponding “exposure” score (1 to 5); this intersection (labeled from Low to High) represents the
combined “value/exposure” ranking. Again, a “low” combined score is represented by the number 1, up
200 Assessing the Vulnerability of Watersheds to Climate Change