watervulnerability

White River National Forest Watershed Vulnerability Assessment, Rocky Mountain Region (R2)
LESSONS LEARNED
The important thing to remember is that this analysis is an attempt to determine the relative vulnerability
of subwatersheds to the anticipated effects of climate change and to give managers a general idea about
geographic areas of concern. It is, by nature, a broad-brush approach, and the level of precision and detail
of the input parameters need to be commensurate with the precision of the final product. To a significant
degree, less is more.
As an example, when the scope of the analysis is being determined, there is inevitably a lot of
brainstorming about what resource values would be affected by certain aspects of a changing climate. The
initial list of resource values can be long. We found that resource issues often had similar sensitivities and
expected responses. For example, two resource values that both respond negatively to decreases in
streamflow are likely to give very similar vulnerability results. In the mountainous region of the Rocky
Mountain west, it may be reasonable to limit resource values to one affected by timing/magnitude of
decreasing flows, one affected by timing/magnitude of increasing peak flows, and/or one affected by
changes in stream temperatures.
Similarly, the list of inherent subwatershed attributes and anthropogenic influences (e.g., geology,
precipitation, roads) that affect the vulnerability of a resource value can also be quite long. Although
many small factors can cumulatively affect resource value vulnerability, they may not exert much
influence in a particular numeric rating scheme. We found that factors with a low influence (assigned
weights) had very little influence on the final rating. It would be a simple matter to do a sensitivity
analysis of the numeric results to see if some attributes could be dropped early in the process, to
streamline the analyses.
Finally, as time goes on, much more detailed data on climate change exposure becomes available. Models
are constantly being tuned and down-scaled to smaller areas. These data have limits based on their
uncertainty, and that uncertainty grows with down-scaling. We structured this analysis so that the actual
values for temperature changes, runoff changes, etc. were not critical. Rather, we focused on the
magnitude and direction of the predicted change. We were more concerned with the direction of change
(increasing or decreasing) and whether that change was a big number or small number relative to the
annual variability that we see now. Not getting lost in the myriad of details of the Variable Infiltration
Capacity model results was easily justified by keeping the original goal of the process in mind.
REFERENCES
Christensen, N. and D.P. Lettenmaier. 2006. A multimodel ensemble approach to assessment of
climate change impacts on the hydrology and water resources of the Colorado River basin. Hydrology and
Earth System Sciences Discussion, 3:1-44.
Merritt, D.M. and N.L. Poff. 2010. Shifting dominance of riparian Populus and Tamarix along gradients
of flow alteration in western North American rivers. Ecological Applications, 20(1): 135-152.
Painter, T.H., J.S. Deems, J. Belnap, A.F. Hamlet, C.C. Landry and B. Udall. 2010. Response of
Colorado River runoff to dust radiative forcing in snow. Proceedings of the National Academy of
Sciences of the United States of America. 6 pp. Full report available at
http://www.pnas.org/content/early/2010/09/14/0913139107.full.pdf+html
128 Assessing the Vulnerability of Watersheds to Climate Change