Post on 19-Dec-2015
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
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)
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
1 2
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.