1. Alan F. Hamlet Andy Wood Dennis P. Lettenmaier JISAO Climate Impacts Group and the Department of Civil Engineering University of Washington September, 2001 Hydroclimatology of the Pacific Northwest and Long-Lead Streamflow Forecasts for the Columbia River Basin for 2002

2. Hydrologic Characteristics of the Columbia Basin Elevation (m) Avg Naturalized Flow The Dalles Flows Originating in Canada Milner

3. Winter Summer

4. Effects of the PDO and ENSO on Columbia River Summer Streamflows Cool Warm

5. PDO/ENSO Effects PDO EffectsENSO Effects Naturalized Flow at The Dalles, OR

6. Naturalized Summer Streamflow at The Dalles

7. Cedar at Chester Morse Lake--PDO Effects

8. Cedar at Chester Morse Lake--ENSO Effects

9. Cedar at Chester Morse Lake--PDO/ENSO Effects

10. Overview of Long-Range Forecasting Methods and Long-Range Forecasts for Water Year 2002

11. Global Climate Models Regional Climate Models Hydrology Models Water Resources Models Overview of Modeling Linkages water demand streamflow temp precip wind downscaling Observed Meteor. Data

15. Time Line for 12-month Lead Time Retrospective Forecasts Climate Forecast Estimated Initial Conditions Forecast Ensemble Lead time = 12 months

16. 1998 cool PDO/warm ENSO

17. 1999 cool PDO/cool ENSO

18. 2000 cool PDO/cool ENSO

19. 2001 cool PDO/ENSO neutral

20. 2002 Forecast Construction Details: Hindcast hydrologic state for August 1, 2001 based on observed weather data VIC driving data from August 1- Sept 30 is taken from 15 observed water years from 1949-2000 associated with winter ENSO neutral conditions in the tropics. This produces 15 forecast ensembles from Oct, 2001 to September, 2002 Experimental Forecasts for 2002 Based on Resampled Observed Driving Data

21. Raw streamflow forecast ensemble at The Dalles compared to 50-year “observed” min, max and mean monthly simulated streamflow. All ENSO neutral. Observed Long Term Mean Highest Observed Lowest Observed

22. Summary of raw streamflow forecast ensemble compared to 50- year “observed” min, max and mean monthly simulated streamflow {whiskers show 90th and 10th percentiles of forecast} Natural Flow at The Dalles

23. Cool PDO/ENSO Neutral Raw Forecast

24. Summary of Cool PDO/ENSO Neutral Raw Forecast

25. 2002 Forecast Construction Details: Hindcast hydrologic state for August 1, 2001 based on observed weather data VIC driving data from August 1, 2001- February 28, 2002 are taken from 20 climate global climate model ensembles. VIC driving data from March 1- September 30, 2002 are based on median 1953 meteorological data This produces 20 forecast ensembles from Oct, 2001 to September, 2002 Experimental Climate Model Driven Forecasts for 2002

26. Climate Model-Based 20-member streamflow forecast at The Dalles 1953 driving data for March-Sept

27. Summary of raw streamflow forecast ensemble compared to 50- year “observed” min, max and mean monthly simulated streamflow {whiskers show 90th and 10th percentiles of forecast}

28. Conclusions: Typical relationships between categorical PDO/ENSO state and PNW winter climate can be exploited to produce useful long lead time streamflow forecasts for PNW rivers using several methods. The 2001 drought has produced unusually dry late summer soil conditions in the Columbia River basin, and winter flows in 2002 are expected to be somewhat below average. ENSO neutral conditions for winter 2002 are most likely to produce near normal summer streamflows at The Dalles. Assumption of cool PDO conditions for winter 2002 increases the likelihood of above average flows and decreases the likelihood of below average flows.

29. Effects to System Storage Retrospective Forecast Method

30. Trends in Regulated Peak Flow at The Dalles Completion of Major Dams

31. Observed System Storage Sept 1, 2001 Observed System Storage April 1, 2001 Obs. 1977-1978 refill sequence full Forecast System Storage: Oct, 2001- Sept, 2002 Firm Energy is met in 3 out of 15 simulations (20% reliability) empty

32. Summary of System Storage Simulation {whiskers are 10th and 90th percentiles} 1977-1978 reference refill

33. Ensemble Average Energy Shortfalls from ColSim Associated with Streamflow Forecast

34. Effects to System Storage Climate Model Based Forecast Method

35. Observed System Storage Sept 1 Forecast System Storage: Oct, 2001- Sept, 2002 Firm Energy is met in 8 out of 20 simulations (40% reliability)

36. Ensemble Average Energy Shortfalls from ColSim Associated with Streamflow Forecast

37. Conclusions Drought conditions in 2001 will increase the likelihood of below average winter flows in 2002 due to reduced soil moistures. Current reservoir contents and limited summer refill in 2001 will produce high vulnerability to capacity-related hydro system shortfalls in winter 2002, and will likely also prevent complete reservoir refill in summer 2002. Normal “firm” energy production from the hydro system is shown to be about 20-40% reliable in the simulations, with most shortfalls occurring in Jan and Feb. Reservoir storage in spring 2002 will be comparable to spring 2001. Expected energy shortfalls (as compared to normal conditions) for winter 2002 are on the order of 850,000 MW-hrs.