F. Hamlet ony L. Westerling P. Barnett is P. Lettenmaier AO/CSES Climate Impacts Group t. of Civil and Environmental Engineering University of Washington ipps Institute of Oceanography ool of Engineering, University of California, Merced Evaluating Recent 20th Century Changes in Cool Season Precipitation Variability in the Western U.S. in the Context of Paleoclimatic Reconstructions
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Alan F. Hamlet Anthony L. Westerling Tim P. Barnett Dennis P. Lettenmaier
Evaluating Recent 20th Century Changes in Cool Season Precipitation Variability in the Western U.S. in the Context of Paleoclimatic Reconstructions. Alan F. Hamlet Anthony L. Westerling Tim P. Barnett Dennis P. Lettenmaier JISAO/CSES Climate Impacts Group - PowerPoint PPT Presentation
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Alan F. HamletAnthony L. WesterlingTim P. BarnettDennis P. Lettenmaier
•JISAO/CSES Climate Impacts Group•Dept. of Civil and Environmental Engineering
University of Washington•Scripps Institute of Oceanography•School of Engineering, University of California, Merced
Evaluating Recent 20th Century Changes in Cool Season Precipitation Variability in the Western U.S. in the Context of Paleoclimatic Reconstructions
Consensus Forecasts of Temperature and Precipitation Changes from IPCC AR4 GCMs
Pacific Northwest
°C
0.4-1.0°C0.9-2.4°C 1.2-5.5°C
Obse
rved 2
0th
centu
ry v
ari
abili
ty
+1.7°C+0.7°C
+3.2°C
Pacific Northwest
%
-1 to +3%-1 to +9% -2 to +21%
Obse
rved 2
0th
centu
ry v
ari
abili
ty
+1% +2%
+6%
-3
-2
-1
0
1
2
3
419
16
1920
1924
1928
1932
1936
1940
1944
1948
1952
1956
1960
1964
1968
1972
1976
1980
1984
1988
1992
1996
2000
Std
An
om
alie
s R
elat
ive
to 1
961-
1990
PNW
CA
CRB
Regionally Averaged Cool Season Precipitation Anomalies
PRECIP
-3
-2
-1
0
1
2
319
16
1920
1924
1928
1932
1936
1940
1944
1948
1952
1956
1960
1964
1968
1972
1976
1980
1984
1988
1992
1996
2000
Std
An
om
alie
s R
elat
ive
to 1
961-
1990
PNW
CA
CRB
Regionally Averaged Warm Season Precipitation Anomalies
PRECIP
2000
3000
4000
5000
6000
7000
8000
9000
1916
1921
1926
1931
1936
1941
1946
1951
1956
1961
1966
1971
1976
1981
1986
1991
1996
2001
Str
eam
flo
w (
cms)
OBS
REG
0
50
100
150
200
250
300
350
400
450
1916
1921
1926
1931
1936
1941
1946
1951
1956
1961
1966
1971
1976
1981
1986
1991
1996
2001
Str
eam
flo
w (
cms)
OBS
REG
R2 = 0.83
R2 = 0.91
Columbia River
Sacramento River
Cool Season Precipitation Explains Most of the Variability in Annual Flow in the PNW and CA
Relationship Between Annual Flow and
Cool Season Precip.
Relationship Between Annual Flow and
Cool Season Precip.
200
300
400
500
600
700
800
900
1000
1100
1916
1921
1926
1931
1936
1941
1946
1951
1956
1961
1966
1971
1976
1981
1986
1991
1996
2001
Str
eam
flo
w (
cms)
OBS
REG
200
300
400
500
600
700
800
900
1000
1100
1916
1921
1926
1931
1936
1941
1946
1951
1956
1961
1966
1971
1976
1981
1986
1991
1996
2001
Str
eam
flo
w (
cms)
OBS
REG
R2 = 0.56
Colorado River
R2 = 0.18
Colorado River
Cool Season Precip Explains Most of the Variability in Annual Flow in the CRB, but the Summer Monsoon Also Plays a Role
Simulated Changes in System Wide Energy Production in the Western U.S.
DJF
Avg
Tem
p (
C)
20-year Flood for “1973-2003” Compared to “1916-2003” for a Consistent Late 20th Century Temperature Regime
X20 ’73-’03 / X20 ’16-’03
X20 ’73-’03 / X20 ’16-’03
Hamlet A.F., Lettenmaier D.P., 2007: Effects of 20th Century Warming and Climate Variability on Flood Risk in the Western U.S., Water Resour.
Res., 43, W06427
Long-Term Comparison of Annual Flow Records from Observations and Paleo Reconstructions
PNW:Observed (naturalized) annual flow in the Columbia River at The Dalles, OR
1858-1877 (reconstructed from observed peak river stage)1878-2003 (naturalized from observed monthly records)
CA:Reconstructed combined annual flow in the Sacramento/San Joaquin basin from tree-ring records.
(Overlapping period 1858-1977)
(Meko, D.M., 2001: Reconstructed Sacramento River System Runoff From Tree Rings, Report prepared
for the California Department of Water Resources, July)
Colorado River Basin:Reconstructed annual flow in the Colorado River at Lees Ferry, AZ from tree ring records.
(Overlapping period 1858-1977)
(Woodhouse, C.A., S.T. Gray, and D.M. Meko, 2006: Updated Streamflow Reconstructions for the Upper
Colorado River Basin, Water Resources Research, Vol. 42, W05415)
-1.5
-1
-0.5
0
0.5
1
1.5
1868
1874
1880
1886
1892
1898
1904
1910
1916
1922
1928
1934
1940
1946
1952
1958
1964
1970
1976
1982
1988
sum lag1 correl
sum inter-regional correl
sum CV
Changes in Streamflow Variability from Long-Term Observations and Paleo Reconstructions (1858-1977)
-1.5
-1
-0.5
0
0.5
1
1.5
1868
1874
1880
1886
1892
1898
1904
1910
1916
1922
1928
1934
1940
1946
1952
1958
1964
1970
1976
1982
1988
sum lag1 correl
sum inter-regional correl
sum CV
Changes in Streamflow Variability from VIC Simulations of Annual Flow (1916-2003)
-1.5
-1
-0.5
0
0.5
1
1.5
1868
1874
1880
1886
1892
1898
1904
1910
1916
1922
1928
1934
1940
1946
1952
1958
1964
1970
1976
1982
1988
sum lag1 correl
sum inter-regional correl
sum CV
Changes in Streamflow Variability from Combined Paleo Reconstructions and VIC Simulations of Annual Flow (1916-2003)
All three metrics high together
Conclusions
•Cool season precipitation is a major driver of annual river flow, hydropower production, and flood risk in the West.
•Substantial and persistent changes in cool season precipitation variability have emerged over the West since about 1975, including increased CV, within-region persistence, and inter-regional correlation.
•Long-term streamflow reconstructions show that the current changes in variability are very unusual in the context of natural variations over the last 150 years or so.
•Can these changes in cool season precipitation be related to changes in circulation associated with greenhouse-forced warming?