watervulnerability

White River National Forest Watershed Vulnerability Assessment, Rocky Mountain Region (R2)
available from Oregon State University was used to determine composite precipitation values for each
subwatershed, weighted by elevation. Since the amount of precipitation a subwatershed receives has a
direct effect on aquatic ecosystems, weighted precipitation is used as a measure on inherent resiliency.
Extent of surface water features. Groundwater movement and storage plays a large role in maintaining
streamflow and stream temperatures. We found that the parent geology was not necessarily a reasonable
predictor of shallow groundwater that regularly interacts with surface water. Instead, the presence of
surface water and springs from the National Hydrography Dataset (NHD) GIS layers was used to estimate
the percentage of a subwatershed with surface water or springs. Because of the buffering effects shallow
groundwater has on aquatic ecosystems, this attribute was also used as a measure of inherent resiliency.
Extent of large-scale pine beetle mortality. In snow-dominated systems, vegetation locally affects
hydrology through evapotranspiration, canopy interception, and extent of snow scour. As the pine beetle
epidemic progresses across western Colorado, we expect to see less evapotranspiration, less canopy
interception, and more redistribution of snow as forest openings increase. Because of these effects on the
annual hydrograph, the percentage of a subwatershed affected by pine beetle mortality was used as a
measure of resiliency to a changing climate.
Anthropogenic Influences in the Project Area Subwatersheds
Human influences can also affect the resiliency of a subwatershed, depending on the amount of
management-related activity that occurs. For the White River National Forest, the following
anthropogenic influences were considered to have potentially significant effects on aquatic resources:
Water uses. The amount of water withdrawn from a steam has a direct effect on the health of the aquatic
system. The more water that is withdrawn, the more stress a system is exposed to and the less resilient it
is to additional changes in water supply. Additionally, changes in streamflow have been associated with a
competitive advantage for invasive species (Merritt and Poff 2010). In order to capture the cumulative
change to the natural hydrology, the number of diversions per square mile was used as a measure of
resiliency to climate change.
Development (primarily roads). Roads and road ditches can have significant effects on how water is
routed across the landscape. Ditches collect surface water (or intercept shallow subsurface water) on hill
slopes, and act as tributary extensions of the stream network. Routing water off the landscape more
quickly would have the net effect of exacerbating anticipated effects of climate change on runoff. In order
to capture the influence of roads on the stream network, the road density, calculated as miles per square
mile, was used as a measure of resiliency to climate change.
Extent of beetle salvage. Performing salvage logging operations to remove standing dead trees can have
additional effects on watershed hydrology. First, removing standing dead trees further reduces the
interception of snow and can increase snow scour as openings increase in size. Additionally, most logging
operations typically involve some new roads, at least temporarily. These effects may be slightly buffered
in the long term since removal of trees may allow for quicker reforestation and subsequent hydrologic
recovery. The percentage of a watershed proposed for salvage logging was used as a measure of
resiliency to climate change.
Step 4. Assess the Relative Vulnerability of the Resource Values
In order for the relative vulnerability among subwatersheds to be determined, each inherent and
anthropogenic attribute needs to be broken into categories of high, medium or low. Then each attribute
121 Assessing the Vulnerability of Watersheds to Climate Change