1. Mid-Range Water Supply Forecasts for Municipal Water Supplies Matthew Wiley, Richard Palmer, and Michael Miller Department of Civil and Environmental Engineering

2. 2 Today’s Presentation Need for forecast Describe approach Present forecasts Introduce Website www.tag.washington.edu

3. 3 Goals Evaluate the value of a 6-month meteorological forecast in making water resources decisions Use meteorological forecast to create a forecast of streamflows Evaluate the meteorological data Evaluate the hydrologic response

4. 4 Seattle Public Utilities Tacoma Water Everett Public Utilities Partner Utilities

5. 5 Problem Setting Project Setting – Puget Sound Region Water supply to 2.6 million Flood Control Navigation Hydropower Environmental

6. 6 Water Supply Utility Challenges Provide safe, reliable and inexpensive drinking water Preserve environmental quality, demonstrate resource stewardship Maintain/enhance Infrastructure Provide stable and economically viable rate structure Adapt to evolving water quality requirements

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8. 8 Primary Purposes of Forecast Refill decisions in spring Supply evaluation in early summer Decisions related to fish flows (when is water most needed) Curtailment decisions in late summer Drawdown decisions in fall

9. 9 Value of Forecast Utility has established operating policies Forecast is valuable if it provides information that modifies policy and forecast is correct Accurate forecasts of normal, below, or above normal are desired (can result in policy change)

10. 10 Approaches Historical Streamflows Assume averages are sufficient Ensemble Streamflow Predictions (ESP) Well-established approach Used by Weather Service Can be conditioned on climate condition

11. 11 ESP Forecast obs Recently Observed Meteorological Data Ensemble of Meteorological Data to Generate forecast ICs Spin-upForecast hydrologic state

12. 12 Approaches National Centers for Environmental Prediction (NCEP) 6-month forecasts Uses Global Climate Model to produce forecast ensembles Can be compared to ESP

13. 13 National Centers for Environmental Prediction (NCEP) climate forecast. Initial and Predicted SST for next 6 months 20 different Initial states of the atmosphere 20 unique forecasts of the climate over the next six months We use the raw model output at this point. 2x2 degree GSM Coupled Ocean-AGCM Official NCEP Climate Forecast Correlation Analysis Past Experience Probability Mapping 20 Ensemble Forecast

14. 14 National Centers for Environmental Prediction (NCEP) climate forecast. Initial and Predicted SST for 6 months 10 different initial states that existed of the atmosphere 10 unique hindcasts of the climate for each year over the next six months We use Hindcasts for bias correction and retrospective analysis 2x2 degree GSM Coupled Ocean-AGCM Official NCEP Climate Forecast (210 hindcasts) Used in conjunction with forecasts for bias correction 10 Ensemble Hindcasts Years 1979 1980 1981 1999 Years 1979 1980 1981 1999 21 years

15. 15 Forecasts being produced ESP NCEP http://www.tag.washington.edu/projects.html

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18. 18 South Fork Tolt River, August 2004, Unconditioned ESP

19. 19 South Fork Tolt River, August 2004, ENSO based ESP

20. Cedar River, August 2004, Unconditioned ESP

21. Cedar River, August 2004, ENSO based ESP

22. 22 Meteorological Forecast

23. 23 Meteorological Forecast

27. 27 Tentative Conclusions Streamflow Forecast In small west slope basins, NCEP is generally more useful than ESP Monthly forecast Poor in December Better in later months of the forecast Seasonal Forecast Better in the spring and early summer Poor in late winter NCEP is in the process of revising its mid- range forecasting procedures

28. 28 Future Work continues Water Temperature Modeling Improve Web Viewing Continue With Forecasts Additional Evaluation of the Quality of the Forecast Conditional evaluations Evaluate other types of Forecasts IRI, CPC

29. 29 Stream Temperature Forecasts

30. 30 Stream Temperature Forecasts

31. 31 Future Work continues Water Temperature Modeling Improve Web Viewing Continue With Forecasts Further Evaluation of Forecast Quality Consider other climate forecasts: IRI, CPC Additional Water Supply Basins White River Bull Run Tualatin

32. 32 Web Page http://www.tag.washington.edu Projects Mid-Range Forecasts