watervulnerability

Grand Mesa, Uncompahgre and Gunnison National Forest Watershed Vulnerability Assessment, Rocky
Mountain Region (R2)
This watershed vulnerability assessment was focused on water-related resources and did not incorporate
predicted changes to terrestrial resources, particularly vegetation, and the implications of warmer
temperatures and potentially reduced precipitation to changes in disturbance regimes (fire, insect, and
disease), shifts in species composition (increase of invasive species) and the resulting viability of existing
vegetation communities. Compounding effects on terrestrial ecosystems can have significant influences
over hydrologic regimes. Similarly, changes in vegetation due to inherent sensitivities (high fire risk) may
have more influence over watershed conditions than climate changes.
What were the most useful data sources?
Climate change reports for the State of Colorado (Ray et al. 2008; Colorado Water Conservation Board
Draft 2010) provided general statewide projections that also provided information relative to the GMUG.
Downscaled information and development of two climate change scenarios (Barsugli and Mearns Draft
2010) served to further describe the range of climate changes that are likely to happen specifically in the
Gunnison Basin; however, the area where the two scenarios may apply included the entire GMUG Forest
area.
VIC data available from the Climate Impacts Group further refined the potential climate changes that may
occur under several different models. Raster data available at the 6 km-grid scale (approximately) were
reviewed to see the elevation differences in parameter outputs. Data were also summarized at the HUC-5
watershed scale. We further summarized data at the geographic-area scale on the GMUG (see Figure 4) to
see how predicted climate changes might occur on different areas of the Forest that had similar climatic
regimes.
What were the most important data deficiencies?
Much of the data assembled concerning values, sensitivities, and stressors were limited to that available
for NFS lands. Some of these data were not complete inventories for the entire GMUG, or the data did not
portray exact locations (e.g., culvert/crossing locations, stream locations, water rights locations). As a
result, the composite rankings are more accurate for those subwatersheds (HUC-6) that occur mostly on
NFS lands, while subwatersheds with larger amounts of off-Forest areas may have erroneous results,
causing the assessment to compound uncertainties. Collaborative efforts with other agencies and
landowners/land managers of non-NFS lands within subwatersheds on the GMUG needs to occur so that
these data gaps can be filled and management implications of climate change can be addressed at a
complete subwatershed/watershed scale.
In an effort to save time and build on previous analyses on the GMUG, we used data compiled in 2005 for
unrelated analyses, and these data were collected at slightly different scales. In some cases, these data are
no longer current. In others, conversion from the scale used in earlier analyses to the modified
subwatershed scale used for the WVA was done mathematically, using weighted averages, rather than
based on spatial data. This introduced further uncertainties into the WVA.
Because of the inherent sensitivities for erosion/sediment production and runoff response of many
subwatersheds on the GMUG, the potential effect of extreme storm events is considered to be a big
vulnerability. There is limited information on extreme storm event frequency and location, and current
climate change models do not provide projections of storm.
Baseline stream temperature data is extremely limited, making it hard to interpret what the potential
effects will be of increased air temperature on stream temperature and changes in cold-water fisheries
habitat.
109 Assessing the Vulnerability of Watersheds to Climate Change