watervulnerability

Grand Mesa, Uncompahgre and Gunnison National Forest Watershed Vulnerability Assessment, Rocky
Mountain Region (R2)
Season Precipitation (%) Temperature (˚C) Temperature (˚F)
Annual -10.0 +3.0 +5.4
Winter ~0.0 +3.0 +5.4
Spring -15.0 +3.0 +5.4
Summer -20.0 +4.0 +7.0
Fall -10.0 +3.0 +5.4
Table 2. Temperature and Precipitation Changes for “More Extreme” Climate Change Scenario
developed by Barsugli and Mearns for the Gunnison Basin
Predicted changes under the “more extreme” scenario include:
1. Increase in annual temperatures of 3 ˚C (5.4 ˚F).
2. A 10% decrease in annual precipitation, with greater decreases in warm season precipitation.
3. Decrease in precipitation and increase in temperature, both act to reduce annual stream flow totals
in the range of 20% to 25%.
4. Warming temperatures lead to a later accumulation of snow in the fall and earlier snowmelt in the
spring. Because this likely represents a hot/dry scenario for much of the west, the potential exists
for more frequent dust deposition events, which also may lead to an earlier melt and to reduced
water yield from the snowpack.
5. Snowmelt-driven stream flow will peak about two or more weeks earlier in the spring, though this
effect may be less if dust effects on snowmelt are strong. The combined effects of dust and
temperature on snowmelt timing tend to be dominated by the dust effects.
6. The much earlier melt, along with decreased summer precipitation and increased summer
temperatures, will result in extremely low amounts of water stored in the soils during summer and
fall.
VIC Model Climate Change Predictions
The primary predictive model used to display climate changes was the VIC hydrologic model. Data
derived using the VIC model were available from the Climate Impacts Group (CIG) at the University of
Washington. Historic trends were developed from the climate record from 1916 to 2006. Future
prediction results for temperature- and precipitation-related parameters were generated using: 1) a
composite of the 10 climate models that best resembled the historic trend, 2) the MIROC_3.2 model
(more extreme temperature increases), and 3) the PCM1 model (less extreme temperatures increases) for
two time periods (2030-2059 and 2070-2099) using the A1B emissions scenario. Data were available at
the ~6 km-grid scale for monthly averages for 21 parameters for each model, but not all parameters were
reviewed by the GMUG team. (Data downloaded from
ftp://ftp.hydro.washington.edu/pub/climate/USFS_monthly_summaries/CO/ on 11/5/2010).
In addition, some of the data were summarized at the HUC-5 scale. (Data downloaded from
ftp://ftp2.fs.fed.us/incoming/gis/PNF/WVA/ on 10/22/2010). Outputs obtained from the VIC Model data
are described below.
84 Assessing the Vulnerability of Watersheds to Climate Change