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.

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

Recap of WY 2007

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

Obs.

Validation of 2007 Forecast

Mod

ified

Flo

w (

cfs)

The Dalles

5000

10000

15000

20000

25000

30000

-3 -2 -1 0 1 2 3 4

Nino 3.4 Anomaly (C)

Apr

il-S

epte

mbe

r A

vg N

atur

aliz

ed

Str

eam

flow

(cf

s)

Natural Flows at Milner 1928-1989

Milner2007Nino3.4 Range0.7 to 1.5

Nat

ural

Flo

w (

KA

F)

Red = long term meanBlue = ensemble meanGray = ensemble membersBlack = range of observations

2007 Forecast for Natural Flow at Milner

Milner2007Nino3.4 Range0.7 to 1.5Warm PDO

Nat

ural

Flo

w (

KA

F)


2007 Forecast for Natural Flow at Milner

Upp

er S

nake

Sto

rage

(K

AF

)

Upp

er S

nake

Sto

rage

(K

AF

)

2007 System Storage Forecasts for the Upper Snake (Oct-Aug)

Nino3.4 Range0.7 to 1.5

Nino3.4 RangeWarm PDO

FullFull

Obs. Storage 9/30/07 (423.8 KAF)

WY 2008 Forecast

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

150000

200000

250000

300000

350000

400000

450000

-3 -2 -1 0 1 2 3 4

NINO3.4 Index Anomaly

Ap

ril-

Se

pte

mb

er

Av

era

ge

S

tre

am

flo

w

1916-2002

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

5000

10000

15000

20000

25000

30000

-3 -2 -1 0 1 2 3 4

Nino 3.4 Anomaly (C)

Apr

il-S

epte

mbe

r A

vg N

atur

aliz

ed

Str

eam

flow

(cf

s)

Natural Flows at Milner 1928-1989

West-Wide Hydrologic Forecast

Mod

ified

Str

eam

flow

(cf

s)

Bias-Adjusted West Wide Forecast at The Dalles (1961-2000)

The Dalles


Nat

ural

Flo

w (

KA

F)


Simulated Natural Flow at Milner (ESP all years)

Milner

Nat

ural

Flo

w (

KA

F)


Simulated Natural Flow at Milner (ESP cool ENSO)

Milner

Upp

er S

nake

Sto

rage

(K

AF

)Full

SnakeSim Storage Forecast (cool ENSO composite)

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.

WY 2007 WY 2008

Potential Implications of ENSO Transition States

1904 1.47

1907 1.00

1921 1.00

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

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

WY Std Ann.

Nat

ural

Str

eam

flow

(cf

s)Based on Dalles Climatology 1901-2003

1932 -0.235

1943 1.137

1965 1.238

1971 2.170

1974 1.686

1984 1.883

1989 -0.080

Historic Milner Apr-Sept streamflow anomalies for water years with previous winter warm ENSO, current winter cool ENSO

WY Std Ann.

Stats:

5 of 7 above 1.1

3 of 7 above 1.7

enso_2008 enso_trans_2008

Based on Milner ESP 1961-2000N

atur

al F

low

(K

AF

)

Nat

ural

Flo

w (

KA

F)

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.

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