1. UW Hydrologic Forecasting: Yakima R. Discussion
Andy Wood
and
Dennis P. Lettenmaier
Department of Civil and Environmental Engineering
for
Washington State Drought Task Force
Olympia, WA
April 25, 2005

2. Presentation Outline 1. UW Experimental Hydrologic Forecasting System
2. Water Year 2005 Assessment for Yakima R. above Parker

3. UW Experimental Hydrologic Forecasting System
funded by
Objective: To create a model-based testbed for evaluating potential sources of improvement in seasonal forecasts since inception of regression/ESP methods
operational seasonal climate forecasts (model-based and otherwise)
greater real-time availability of station data
computing advances
new satellite-based products (primarily snow cover)
distributed, physical hydrologic modeling for macroscale regions

4. UW Forecasting: Model used to estimate conditions
Snowpack
Initial Condition
Soil Moisture
Initial Condition

5. UW Forecasting: SNOTEL merged with model SWE
The pattern of observed SWE values, which are merged with the forecast initial conditions, is generally in good agreement with the VIC simulated snow state.
The PNW currently has had near record low snowpacks, while the Southwest and California have had record high snowpacks.

6. UW Forecasting: Streamflow simulations calibrated
VIC model runoff is routed to streamflow gages, and verified against observations

7. UW Forecasting: Sample Streamflow ‘Products’
locations
monthly
hydrographs
targeted statistics
e.g., runoff volumes

8. UW Forecasting: Sample Spatial Forecasts
Precip
Temp
SWE
Runoff
Soil Moisture
Mar-05
Apr-05
May-05

9. Comments on Yakima Basin forecasts
1. We do not yet have calibrated streamflow forecasts for the Yakima R. basin, but have started working on 3 gages (more are possible).
2. We have water-balance forecasts produced by averaging variables over the model grid cells in the basin.
3. Without full model calibration, these are best used for seasonal (summer) runoff (hence streamflow) forecasts, since the weekly/monthly timing may not be accurate.
Yakima R. at Cle Elum
Naches R. at Naches
Yakima R. nr. Parker

10. Presentation Outline 1. UW Experimental Hydrologic Forecasting System
2. Water Year 2005 Assessment for Yakima R. above Parker
- April 1, Western US conditions
- April 15, conditions for PNW only
- basin-averaged forecasts for Yakima R. near Parker, WA

11. WY2005, Apr. 1 hydrologic conditions

12. WY2005, Apr. 15 hydrologic conditions
Snow Water Equivalent
(Yakima nr Parker basin highlighted)
value (mm)
% of normal
percentile

13. WY2005, Apr. 15 hydrologic conditions
Soil Moisture
(Yakima nr Parker basin highlighted)
note: it appears headwaters have elevated SM, perhaps from recent early melt
value (mm)
% of normal
percentile

14. 4/15 ESP forecast: WY2005 Precip, Temp
plots show current + forecast
(ESP; min, max and quartiles)
against historical
min, max and quartiles
Yakima R. Basin near Parker, WA

15. 4/15 ESP forecast: WY2005 SM, SWE, RO
Apr-Sep % of avg
3/15 4/15 chg
max 61 57
min

16. Forecast Summary
ESP forecast is ~50% chance of 42-50% of normal summer runoff.
Precip. has fed SM and runoff instead of snow, so Jun-Jul-Aug. will be hit worse than Apr-May.
Situation has improved since 1 month ago, slightly: forecast median hasn’t changed much but the lowest forecasts from 1 month ago are no longer possible.
Snowpack state is extremely low, but soil moisture appears to be near or slightly above normal, which will offset the effects of the low snowpack in the near term.

17. Questions?
website:
/ Lettenmaier / Projects / fcst /
contact: Andrew Wood
Research Assistant Professor
Dept. Civil and Environmental Engineering
Hydrology and Water Resources