watervulnerability

Grand Mesa, Uncompahgre and Gunnison National Forest Watershed Vulnerability Assessment, Rocky
Mountain Region (R2)
Consumptive water use values (public and private water rights for irrigation, domestic and stock water
use, and source water protection areas for communities) are vulnerable due to predicted changes in
temperature and precipitation. Increased temperatures can alter the timing of runoff and lengthen the
season of demand for water in the spring and fall. Aridity indices are expected to decrease even if
precipitation does not change, because warmer temperatures will result in increased evapotranspiration.
The result is potentially less available water for ecological processes and human use. Predicted reductions
in annual precipitation, along with the potential for longer and more frequent droughts, further reduce
water availability. Water will be most limited in those areas with aridity indices below 1.0 (Uncompahgre,
West Elk, and Cochetopa). If these landscapes become more arid, existing water developments may no
longer hold water, potentially reducing livestock management opportunities. Consumptive water uses on
the Grand Mesa geographic area may be most vulnerable, because the aridity index is predicted to
decrease to less than 1.0. It is not clear how the large concentration of existing waterbodies and associated
riparian/wetland habitats found on the Grand Mesa may buffer predicted effects.
Aquatic Ecological Values Vulnerability
Similar to water use values discussed above, aquatic ecological values are vulnerable to predicted climate
changes in several ways. Aquatic values, such as fisheries and riparian/wetland habitats associated with
streams, are vulnerable to flooding and sediment/debris loading. Risk is exacerbated in subwatersheds
that have inherent sensitivity and are impacted by past management activities. Aquatic Ecological Values
related to Erosion Sensitivity × Activity Stressors are shown in Figure 30. The areas where erosion or
sediment potential has the highest risk of affecting aquatic ecological values are highest in the Upper
Taylor and San Juans geographic areas. Aquatic Ecological Values related to Runoff Response Sensitivity
× Activity Stressors are shown in Figure 31. The areas where runoff potential has the highest risk of
affecting aquatic ecological values are in the San Juans geographic area, with smaller groupings of
subwatersheds in the remaining geographic areas.
Flooding due to earlier and/or rapid runoff can result in scouring out of aquatic habitats, resulting in loss
of vegetation and other habitat features, as well as flushing resident trout or eggs out of the most suitable
habitats. Increased sediment loads could fill in aquatic habitats and riparian areas, as well as smother
nesting gravels for stream-dwelling fish. Debris flows simplify channel habitats through removal of banks
and large wood, especially in headwater streams with moderate to high gradient. Wetlands and offchannel
habitats become filled with sediment, reducing the size and functionality of these habitats.
Subwatersheds with aquatic ecological values in the Upper Taylor and San Juans geographic areas are
most vulnerable to these combined effects.
104 Assessing the Vulnerability of Watersheds to Climate Change