watervulnerability

Chugach National Forest Watershed Vulnerability Assessment, Alaska Region (R10)
Figure 3. An example of the community graphs provided by SNAP. The black bars show the amount of variation
among the five models used for these projections. Graphs are also available for precipitation and with projections for
low and high emissions scenarios as well.
The predicted changes to hydrologic processes were only examined qualitatively. In part, this was due to
the limited availability of personnel, hydrologic models for Alaska, and stream gauge data. Moreover, the
available quantity of water does not appear to be a problem in Alaska as it is in other areas. The climate
models call for increased precipitation in all months of the year and the relatively high average elevations
of the watersheds would appear to buffer potential changes in snowmelt and runoff timing.
To determine effects on water resources and values, I investigated the use of the NetWeaver
knowledge-based decision support system. The appeal of this and similar systems is that they can
incorporate empirical data as well as “expert opinion” in a logical transparent method. I thought this
might be useful given the limited amount of available data for current and historic stream flows, water
temperatures, and other parameters. It might also have been useful for comparing conditions across
watersheds, since the system output is a numerical score measuring how “true” a certain proposition
might be – for example, “Watershed X can sustain a viable coho salmon population.”
The usefulness of this method, however, is limited by the complexity of the situation, how qualitative
input is scaled (high, medium, low or numerically), and the confidence the experts have in making a
rating or judgment. In short, this method did not prove to be practical and the analysis was not completed.
My experience, however, provides a practical lesson for land managers that will be addressed in the
assessment section.
Further determination of the effects on aquatic resources and values, and the overall watershed risks, were
made qualitatively, based on information in the literature, consideration of stressors and buffers, current
investigations in the area, and personal communications. The issues are complex and there is a great deal
of uncertainty, especially with the biological effects. These will be presented in the discussion.
273 Assessing the Vulnerability of Watersheds to Climate Change