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.
Obs.

5. Ensemble Streamflow Forecast for the Columbia River at The Dalles for WY (Nino3.4 anomalies between 0.7 and 1.5)
Black = Climatological Extremes
Gray = Forecast Ensemble Members
Red = LTM from
Blue = Ensemble Mean
Modified Flow (cfs)

6. Validation of 2007 Forecast
Modified Flow (cfs)

7. ColSim Reservoir System Storage Forecast
All Years from for which J. Nino3.4 Anom. >= 0.7 AND <= 1.5
Obs Storage
Sept 30, 2007
45.86 MAF
2007

8. WY 2008 Forecast

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

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

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

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

14. West-Wide Hydrologic Forecast

15. Bias Adjusted West Wide Forecast (1961-2000)
Modified Streamflow (cfs)

16. Bias Adjusted West Wide Forecast (1961-2000)
Modified Streamflow (cfs)

17. Bias Adjusted West Wide Forecast (1961-2000)
[ to ]
Modified Streamflow (cfs)

18. ColSim Storage Forecast (cool ENSO composite 1961-2000)

19. Conclusions:
The WY 2007 ESP forecast predicted increased likelihood of drought. Observed summer flows in 2007 were below average and were close to the ensemble forecast mean (skillful forecast).
A moderate to strong cool ENSO event is expected for the winter of , which historically is associated with increased likelihood of above average Apr-Sep flow at The Dalles.
Dry initial soil conditions in the basin are projected to systematically reduce natural flows from Jan-July for water year 2008 by about 8 percent. The combined forecast is for near normal conditions, because the cool ENSO signal and soil moisture signal are roughly equal and in opposite directions.

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

21. Historic Dalles Apr-Sept streamflow anomalies for water years with previous winter warm ENSO, current winter cool ENSO
1904
1.47
1907
1.00
1921
1925
0.49
1932
0.39
1943
0.88
1965
0.90
1971
1.55
1974
2.22
1984
0.58
1989
-0.40
1996
0.93
1999
0.89
Stats:
12 of 13 above 0.39
11 of 13 above 0.49
9 of 13 above 0.88

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