1. Recap of Water Year 2007 Hydrologic Forecast and Forecasts for Water Year 2008 Alan F. Hamlet Andrew W. Wood Dennis P. Lettenmaier JISAO/CSES Climate Impacts Group Dept. of Civil and Environmental Engineering University of Washington

2. Recap of WY 2007

3. http://www.ecmwf.int/products/forecasts/d/charts/seasonal/forecast/plumes/ Obs.

5. Validation of 2007 Forecast Modified Flow (cfs) The Dalles

6. Natural Flows at Milner 1928-1989

7. Milner 2007 Nino3.4 Range 0.7 to 1.5 Natural Flow (KAF) Red = long term mean Blue = ensemble mean Gray = ensemble members Black = range of observations 2007 Forecast for Natural Flow at Milner

8. Milner 2007 Nino3.4 Range 0.7 to 1.5 Warm PDO Natural Flow (KAF) Red = long term mean Blue = ensemble mean Gray = ensemble members Black = range of observations 2007 Forecast for Natural Flow at Milner

9. Upper Snake Storage (KAF) 2007 System Storage Forecasts for the Upper Snake (Oct-Aug) Nino3.4 Range 0.7 to 1.5 Nino3.4 Range Warm PDO Full Obs. Storage 9/30/07 (423.8 KAF)

10. WY 2008 Forecast

11. http://www.ecmwf.int/products/forecasts/d/charts/seasonal/forecast/seasonal_range_fo recast/nino_plumes_public_s3!3.4!200709!/

12. 1916-2002 April-September Naturalized Flow for the Columbia River at The Dalles, OR from Historic Water Years vs January Nino 3.4 Anomalies.

13. Natural Flows at Milner 1928-1989

14. West-Wide Hydrologic Forecast

15. Modified Streamflow (cfs) Bias-Adjusted West Wide Forecast at The Dalles (1961-2000) The Dalles Red = long term mean Blue = ensemble mean Gray = ensemble members Black = range of observations

16. Natural Flow (KAF) Red = long term mean Blue = ensemble mean Gray = ensemble members Black = range of observations Simulated Natural Flow at Milner (ESP all years) Milner

17. Natural Flow (KAF) Red = long term mean Blue = ensemble mean Gray = ensemble members Black = range of observations Simulated Natural Flow at Milner (ESP cool ENSO) Milner

18. Upper Snake Storage (KAF) Full SnakeSim Storage Forecast (cool ENSO composite)

19. Conclusions: The WY 2007 ESP forecast predicted increased likelihood of drought. Observed summer flows at Milner in 2007 were strongly below average (~55% of normal for April-Sept) and were towards the bottom of the ensemble. A moderate to strong cool ENSO event is expected for the winter of 2007-2008, which historically is associated with increased likelihood of above average Apr-Sep flow at Milner. Dry initial soil conditions in the basin are projected to systematically reduce natural flows at Milner from April-Sept for water year 2008. However even with dry soils, the forecast at Milner shows increased chance of high flows. Snakesim model simulations suggest increases in carry over storage in the upper Snake in Sept 2008 above about 1.0 MAF.

20. WY 2007WY 2008 Potential Implications of ENSO Transition States

21. 19041.47 19071.00 19211.00 19250.49 19320.39 19430.88 19650.90 19711.55 19742.22 19840.58 1989-0.40 19960.93 19990.89 Historic Dalles Apr-Sept streamflow anomalies for water years with previous winter warm ENSO, current winter cool ENSO Stats: 12 of 13 above 0.39 11 of 13 above 0.49 9 of 13 above 0.88 WYStd Ann.

22. Natural Streamflow (cfs) Based on Dalles Climatology 1901-2003

23. 1932-0.235 19431.137 19651.238 19712.170 19741.686 19841.883 1989-0.080 Historic Milner Apr-Sept streamflow anomalies for water years with previous winter warm ENSO, current winter cool ENSO WYStd Ann. Stats: 5 of 7 above 1.1 3 of 7 above 1.7

24. enso_2008enso_trans_2008 Based on Milner ESP 1961-2000 Natural Flow (KAF)