BOARD00043 ‎(3)‎

• Board Meeting Date: 9/19/2006
• Description: CF Section - Finance Subcommittee Meeting
• Board Meetings - Doc Type: Meeting

Description of project:
Streamflow in Colorado is driven primarily by the springtime melting of deep
snowpacks that accumulate during the winter. Recent studies of streamflow timing in the
Western United States indicate that over the past 50 years, snowmelt runoff in much of
the West is occurring earlier than in the past. The analysis noted that changes were most
pronounced in the Sierra Nevada, Cascades, and northern Rocky Mountains, and only
minor changes in streamflow timing were identified in Colorado, suggesting that the state
was relatively immune to climate change due to the state's cold snowpacks and high
elevations. The study raised important issues about the potential effects of climate change
on water supplies in the west, but the results for Colorado were somewhat puzzling given
local perceptions that recently, melt has been occurring earlier in Colorado as well.
Additionally, the previous studies inferred earlier snowmelt based on changes in runoff
timing, rather than by analyzing actual snowpack data.
The USGS, Colorado Water Science Center would like to conduct and publish a
detailed analysis of snowpack melt timing, streamflow runoff timing, and trends in
monthly air temperature and precipitation in high-elevation areas in Colorado. The
objective is to document recent trends in snowmelt and runofftiming, and to quantify
how those pa.rameters are affected by changing climate. Snowmelt timing would be
analyzed for the period of record (1978 - present) using data from 72 SNOTEL sites in
the state; streamflow timing would be analyzed for the same period using 50 headwater
streams with minimal or no diversions. All ofthe major river basins in the western part
of the state, including those in the Front Range, would be covered. Climate data would
be obtained from meteorologic stations co-located with the SNOTEL sites. Trend
analyses would be conducted using anew, robust statistical method called the Regional
Kendall Test, which provides increased power of trend detection in short records with
substantial inter-annual variability. Results will be used to estimate potential changes in
runoff amount and timing under a variety of climate change scenarios.

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