watervulnerability

Grand Mesa, Uncompahgre and Gunnison National Forest Watershed Vulnerability Assessment, Rocky
Mountain Region (R2)
Climate change projections for the State of Colorado are summarized in “Climate Change in Colorado: A
Synthesis to Support Water Resources Management and Adaptation” (Ray et al. 2008) and include the
following projections.
1. In Colorado, temperatures have increased about 2 ˚F in the past 30 years. Climate models project
Colorado will continue to warm 2.5 ˚F [+1.5 to +3.5 ˚F] by 2025, relative to the 1950-99 baseline,
and 4 ˚F [+2.5 to +5.5 ˚F] by 2050. The 2050 projections show summers warming by +5 ˚F [+3 to
+7 ˚F], and winters by +3 ˚F [+2 to +5 ˚F].
2. Winter projections show fewer extreme cold months, more extreme warm months, and more
strings of consecutive warm winters.
3. In all seasons, the climate of the mountains is projected to migrate upward in elevation, and the
climate of the desert southwest is projected to progress up into the valleys of the Western Slope.
4. Variability in annual precipitation is high and no long-term trend in annual precipitation has been
detected for Colorado. Multi-model average projections show little change in future annual mean
precipitation, although seasonal shift in precipitation does emerge.
5. Dramatic declines in lower-elevation (< 8,200 ft) snowpack are projected, due to more winter
precipitation coming as rain than snow. Modest declines in snowpack are projected (10%-20%)
for Colorado’s high-elevations (> 8,200 ft) by 2050.
6. Between 1978 and 2004, the onset of spring runoff from melting snow has shifted earlier by two
weeks. By 2050, the timing of runoff is projected to shift earlier in the spring, and late-summer
flows may be reduced. These changes are projected to occur regardless of changes in
precipitation.
7. The Upper Colorado River Basin average runoff is projected to decrease as much as 20% by
2050, compared to the 20 th century average.
8. Increased storm intensity and variability are projected to elevate risks for floods and droughts.
9. Increasing temperature and soil moisture changes may shift mountain habitats higher in elevation.
Forest, rangeland, and riparian plant communities may change with more xeric, drought-tolerant
species becoming more abundant.
10. More extensive wildfire activity, especially at lower elevation/fire dominated ecosystems is
predicted.
11. Decreased snowpack and earlier spring melt could diminish recharge of subsurface aquifers that
support late summer and winter baseflows.
Downscaled Scenarios for Gunnison Basin for 2040-2060
Downscaled climate changes were also available for the GMUG. Barsugli and Mearns (Draft 2010)
developed two climate change scenarios for a Climate Change Adaptation Workshop for Natural
Resource Managers in the Gunnison Basin, facilitated by The Nature Conservancy. These scenarios were
specifically designed to represent a “moderate” and a “more extreme” scenario for the 2040-2060
timeframe. These scenarios were designed using the A2 emissions scenario because the world is already
on this scenario path. Two hydrologic change scenarios were developed in tandem with the climate
change scenarios, which produced quantitative estimates of how soil moisture, snowpack, and runoff
would change, consistent with the temperature and precipitation change scenarios. These hydrologic
scenarios were developed using the Sacramento Soil Moisture Accounting hydrology model, coupled to
the “Snow-17” snow model, developed by the NOAA.
82 Assessing the Vulnerability of Watersheds to Climate Change