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• Board Meeting Date: 7/22/2008
• Description: Directors' Reports - CWCB Director
• Board Meetings - Doc Type: Memo

the Rio Grande Basin". This project was a small extension of the larger CWCB funded effort that has
been ongoing for the last four years. In the main Project we are in Phase III that links SNODAS to an
experimental distributed hydrologic model for comparisons of products and streamflow forecasts to those
of the Colorado Basin River Forecast Center.
SNODAS model outputs offer several benefits over SNOTEL observations including spatially continuous
estimates of snow cover characteristics as well as estimates of transport processes like snowmelt and
sublimation that affect whether snow ablation is available for runoff. Simply put the CWCB was working
with RTI to provide the Division of Water Resources with weekly tools and data to track the monthly
NRCS Basin Outlook reports that serve as the official water supply forecasts.
RTi collected and processed SNODAS, streamflow, natural flow, forecasts, SNOTEL and climate data for
the Rio Grande Basin and provided weekly GIS mapping and spreadsheets of SNOTEL and SNODAS
data for May and June 2008. RTi also performed a limited investigation of the NRCS seasonal water
supply forecasts for the Rio Delco forecast point.
The investigation of NRCS official water supply forecasts focused on WY 2005 and 2007 due to the high
and low discrepancies between the forecasts and observed runoff values. The summary from this project
is that the surface sublimation and condensation product from SNODAS shows potential for predicting
snow losses that do not translate into streamflow. A monthly water balance analysis indicated that four
variables may contribute between actual and forecasted seasonal runoff volumes: soil moisture, summer
precipitation, snowmelt timing and sublimation.
Recommendations from the RTi report are to continue processing he SNODAS data and produce weekly
data for WY 2009 melt season that include SWE and sublimation information; develop the water balance
spreadsheet into an extra forecasting tool, implement a hydrologic model that has soil moisture
accounting, graph SNODAS SWE by elevation band to show changes in snow distribution over time, and
utilize SNODAS data to identify gaps in existing monitoring networks. At the completion of the project
it was agreed by the DWR, CWCB, NRCS, and RTi that SNODAS data does provide value added to
SNOTEL data and the existing water supply forecasts. For copies of this report search the WRIC or
contact Michelle Garrison or Joe Busto on CWCB staff. The graphic is an example of the weekly
product that was a GIS map provided to the DWR staff that delineated the sub basins, calculated
snowpack snow water equivalent at a point in time in a sub basin above a forecast point and provided the
SWE change from the previous week. (Tom Browning)
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