BOARD00070 ‎(2)‎

• Board Meeting Date: 11/13/2006
• Description: En-Bloc Non Reimbursable Investments USGS Snowmelt Timing Study
• Board Meetings - Doc Type: Memo

ST A TE OF COLORADO

Colorado Water Conservation Board

. Department of Natural Resources
I~B Sherman Street, ROO1l1 721
Denver, Cnlor<ldo 110203
Phone: (~03) H6n-~+l1
FAX: (~03) Hb6-!-!7-!
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MEMORANDUM

Bill Owens
Governor

TO: -- -- -----C6rorado Water Conservafion Board- ~----- -
FROM :-- - - Michelle Garrison, Wat~r Supply Protection Program

Russell George
Executive-Director

Rod Kuharich
CWCS Director

DATE:
RE:

November 13. 2006
Agenda Item 11f: En-Bloc Non-Reimbursable Investments
USGS Snowmelt Ti!l1i!,g ~~udy

Dan McAuliffe
Deputy Director

Introduction

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 identitied in Colorado. 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 occLlrring earlier in Colorado as well.

Because of the puzzling results for Colorado, the USGS Colorado Water Science Center conducted preliminary
analyses on a dozen SNOTEL and streamflow sites in selected river basins in Colorado. Results indicate that
snowmelt and runoff are occun'ing earlier at almost all of the sites that were tested, in some cases by as much as 2
weeks. There appear to be important regional variations in the snowmelt- and runoff-timing trends, with relatively
strong trends in the Animas and Arkansas river basins and weaker trends in the South Platte river basin. Changes in
snowmelt timing at the pilot study sites were strongly correlated with increasing springtime air temperatures. These
preliminary results suggest a more detailed analysis is warranted, which could provide new information having
important implications for water resource management and availability in Colorado.

Discussion

The USGS Colorado Water Science Center proposes a detailed analysis of snowpack melt timing, streamtlow
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 runoff timing, and to quantify how those parameters are
affected by changing climate. Snowmelt timing will be analyzed for selected SNOTEL sites and streamtlow timing
will be analyzed for selected headwater streams with minimal or no diversions. All of the major river basins in the
westem part of the state, including those in the Front Range, will be covered. Climate data will be obtained from
meteorologic stations co-located with the SNOTEL sites, and trend analyses of monthly air temperature and
precipitation will be conducted. Results will be used to estimate potential changes in runoff amount and timing
under a variety of climate change scenarios to understand possible implications to water resources in Colorado
including changes in water use, reservoir operations, timing and magnitude of snowmelt flooding, drought
response, and availability of flow at certain times to meet in stream flow rights.
.

Flood rrotection . Water Supply rlanning and Finance. Sh'eam and Lake Protection
Water Supply Protection. Conservation and Drought Planning