Alan F. HamletNate MantuaTodd Mitchell •JISAO/CSES Climate Impacts Group•Dept. of Civil and Environmental Engineering

University of Washington

ENSO Transition and the Potential for Extremely Wet Winters in the PNW

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

Nino 3.4 Forecast (2010)

Nino 3.4 Forecast (2011)

Nino 3.4 Forecast (2011)

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

Stats:

12 of 14 above 0.39

11 of 14 above 0.49

9 of 14 above 0.87

Water Year Average April-Sept Flow (cfs)

Anomaly(cfs)

Std. Anomaly (number of standard deviations from the mean)

1904 381769 82595 1.4659411907 355726 56552 0.9983251921 355607 56433 0.9961921925 327301 28127 0.4879461932 321917 22743 0.3912691943 348757 49583 0.8731951965 350140 50966 0.8980331971 386065 86891 1.5430851974 423785 124611 2.2203581984 332255 33081 0.5768991989 277693 -21481 -0.402791996 353565 54391 0.9595331999 350530 51356 0.9050322006 310757 10631 0.190885

Nat

ural

Str

eam

flow

(cf

s)Based on Dalles Climatology 1901-2003

Warm season flow in 2008 was slightly above the long term mean.

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 Deviations from the Mean

Stats:

5 of 7 above 1.1

3 of 7 above 1.7

enso_2008 enso_trans_2008

Based on Milner ESP 1961-2000

Nat

ural

Flo

w (

KA

F)

Nat

ural

Flo

w (

KA

F)

Emerging Prospects for Long-Term Predictability

Source: Okumura, Y.M. and C. Deser, 2010: Asymmetry in the Duration of El Niño and La Niña, http://journals.ametsoc.org/doi/pdf/10.1175/2010JCLI3592.1

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3 4 5 6 7

8 9 10 11 12

7/12 warm ENSO events above 1.0

threshold are followed by cool ENSO events

5/12 warm ENSO events above 1.0 are followed by

cool ENSO events below 1.0

Conclusions

Water year pairs with ENSO transitions from warm to cool phase in a single year are strongly associated historically with above average flow in Columbia and Snake Rivers in the second (cool ENSO) year.

Historically such paired (warm/cool) events are more likely to occur when a strong (above 1.0 std deviation) warm event occurs.

Thus increased odds of above average flow are predictable with very long lead times of up to 24 months under certain conditions. In June 1997, with a strong warm ENSO event clearly underway, elevated odds of high flows in warm season 1999 would have been predicted, for example.

These kinds of long range forecasts have potentially useful application to water resources management problems. In particular, the amount of storage that can be safely used during low flow conditions in warm ENSO years is arguably a function of the strength of the warm ENSO event.