watervulnerability

Grand Mesa, Uncompahgre and Gunnison National Forest Watershed Vulnerability Assessment, Rocky
Mountain Region (R2)
Fisheries and aquatic habitats can be directly affected by the predicted changes in temperature and
precipitation. Temperature increase may have both negative and positive effects on cold-water fisheries in
general and on cutthroat trout populations in particular. Occupied habitats at lower elevations may be
eliminated as stream temperatures increase due to increases in air temperatures. The loss of cold-water
fisheries may allow an expansion of occupied habitat for several sensitive species (e.g., bluehead sucker,
roundtail chub) currently only found in streams and rivers at lower elevations. Increases in stream
temperatures at higher elevations may actually benefit fish populations by making these streams more
productive due to increasing growth rates of the fish that occupy them. Our current thinking is that low
water temperatures in high-elevation streams limit fish growth and recruitment. Because current stream
temperature data are lacking for most of the Forest, it is unknown if and specifically where low stream
temperature could be having these effects. In 2011, the Forest began a multi-year project to collect and
summarize baseline stream temperature data. The collection effort will focus on streams that support
conservation populations of cutthroat trout; however, additional streams will be sampled in order to
develop a robust dataset from which changes in stream temperature may be modeled.
Botanical aquatic habitats (fens, wetlands, riparian areas) can also be directly impacted by predicted
changes in temperature and precipitation, in much the same way water use values were affected. Predicted
increases in temperature, associated increases in evapotranspiration, and decreases in aridity indices will
all result in reducing water availability. Prolonged drought will further reduce groundwater recharge.
Aquatic habitats in areas where these changes are more pronounced will be most vulnerable. Aquatic
habitats are currently limited in the drier geographic areas (Uncompahgre, West Elk, Cochetopa) and are
likely to become even more so. Aquatic habitats on the Grand Mesa may be most vulnerable because the
aridity index is predicted to drop from above 1 to below 1.
In reviewing the six previous figures, some areas have high risk much more often than others. Figure 32
displays a count of how often a given subwatershed has a high risk ranking for the combination of values,
sensitivities, and stressors. The San Juans geographic area has the largest area (339,717 acres) and largest
number of subwatersheds (9) that received “High” rankings for all combinations of values, sensitivities,
and stressors. The Upper Taylor geographic area has the largest area (476,936 acres) of subwatersheds
with three or more “High” risk rankings.
106 Assessing the Vulnerability of Watersheds to Climate Change