alan f. hamlet philip w. mote martyn clark dennis p. lettenmaier jisao/sma climate impacts group and...
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Alan F. HamletPhilip W. MoteMartyn Clark
Dennis P. Lettenmaier
JISAO/SMA Climate Impacts Groupand Department of Civil and Environmental Engineering
University of Washington
May 20, 2004
Effects of Temperature and Precipitation Variability on Snowpack
Trends in the Mountain West
Motivation
April 1 SWE (mm)
Current Climate “2020s” (+1.7 C) “2040s” (+ 2.5 C)
-44% -58%
Changes in Simulated April 1 Snowpack for the Cascade Range in Washington and Oregon
0
1000
2000
3000
4000
5000
6000
7000
8000
900010
/1
10/2
9
11/2
6
12/2
4
1/21
2/18
3/18
4/15
5/13
6/10 7/8
8/5
9/2
Date
Infl
ow
(ac
re-f
t) Simulated 20thCentury Climate
2020s ClimateChange Scenario
2040s ClimateChange Scenario
Hydrologic effects to the Cedar Riverfor “Middle-of-the-Road” Scenarios
+ 1.7 C
+ 2.5 C
Man-made storage ~ 10% of annual flow
If global warming has affected the PNW significantly over the 20th century, we should see it in the Cascades in the historic snow and streamflow records.
What can we say about less sensitive areas?
Why Do We Need Model Simulations of the Historic Record?
•Longer Record (Avoids problems with PDO from 1950-1997)
•Spatial Coverage (high and low elevations not in the observations)
•Temporal Resolution (daily time step)
•Consistency between temp, precip, SWE, and streamflow
•Explicit sensitivity analysis for effects of temperature and precipitation
150000
200000
250000
300000
350000
400000
450000
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200
0
Ap
r-S
ept F
low
(cfs
)
Effects of the PDO and ENSO on Columbia River Summer Streamflows
Cool CoolWarm Warm
PDO
Red = Warm ENSO Green = ENSO neut. Blue = Cool ENSO
Snow Model
Schematic of VIC Hydrologic Model and Energy Balance Snow Model
PNW
CACRB
GB
Preprocessing Regridding
Lapse Temperatures
Correction to RemoveTemporal
Inhomogeneities
HCN/HCCDMonthly Data
Topographic Correction forPrecipitation
Coop Daily Data
PRISM MonthlyPrecipitation
Maps
Schematic Diagram for Data Processing of VIC Meteorological Driving Data
Preprocessing Regridding
Lapse Temperatures
Correction to RemoveTemporal
Inhomogeneities
HCN/HCCDMonthly Data
Topographic Correction forPrecipitation
Coop Daily Data
PRISM MonthlyPrecipitation
Maps
Preprocessing Regridding
Lapse Temperatures
Correction to RemoveTemporal
Inhomogeneities
HCN/HCCDMonthly Data
Topographic Correction forPrecipitation
Coop Daily Data
PRISM MonthlyPrecipitation
Maps
Schematic Diagram for Data Processing of VIC Meteorological Driving Data
Result:Daily Precipitation, Tmax, Tmin
1915-1997
Met Data1915-1997
VIC SWELinear Trend
Analysis
Overview of Simulation and Analysis
•1916-1997 •1924-1946 (cool to warm PDO)•1947-1997 (warm to cool PDO)•1924-1946 with 1977-1995 (warm to warm PDO)
Linear Trends:
Experiments:•Base—combined effects of temp and precip trends•Static Precip—effects of temperature trends only•Static Temp—effects of precipitation trends only
Source: Mote et al. (2004)
Trends in April 1 SWE 1950-1997
Trend %/yr
DJF
T
(C
)
Trend %/yr
DJF
T (
C)
Trend %/yrD
JF T
(C
)
Mar 1 Apr 1 May 1
Trend %/yr Trend %/yr Trend %/yr
Red = PNWBlue = CAGreen = COBlack = GBAS
1916-1997
Relative Trend in April 1 SWE
(% per year)
1916-1997
DJF
AV
G T
(C
)
Relative Trend in April 1 SWE
(% per year)
1916-1997Effects of Temp
DJF
AV
G T
(C
)
Relative Trend in April 1 SWE
(% per year)
1916-1997Effects of Precip
DJF
AV
G T
(C
)
Fig 31916-1997
A)
B)
C)
Trend %/yr
Trend %/yr
Trend %/yr
djf
avg
T (
C)
djf
avg
T (
C)
djf
avg
T (
C)
Trend %/yr
Trend %/yr
Trend %/yr
Both Temp and Precip
Precip Effects Only
Temp Effects Only
Fig 41924-1976
A)
B)
C)
Trend %/yr
Trend %/yr
Trend %/yr
djf
avg
T (
C)
djf
avg
T (
C)
djf
avg
T (
C)
Trend %/yr
Trend %/yr
Trend %/yr
Both Temp and Precip
Precip Effects Only
Temp Effects Only
Fig 51947-1997
A)
B)
C)
Trend %/yr
Trend %/yr
Trend %/yr
djf
avg
T (
C)
djf
avg
T (
C)
djf
avg
T (
C)
Trend %/yr
Trend %/yr
Trend %/yr
Both Temp and Precip
Precip Effects Only
Temp Effects Only
Fig 61924-1946with1977-1995
A)
B)
C)
Trend %/yr
Trend %/yr
Trend %/yr
djf
avg
T (
C)
djf
avg
T (
C)
djf
avg
T (
C)
Trend %/yr
Trend %/yr
Trend %/yr
Both Temp and Precip
Precip Effects Only
Temp Effects Only
Physical Characteristics of the Mountain West
Elevation (m) DJF Temp (C) NDJFM PCP (mm)
Figure 7
1
2
3
Region 1 (Coastal)Region 2 (Inland)Region 3 (Interior)
Region 1
Region 2
Region 3
Trend %/yr
Trend %/yr
Trend %/yr
Trend %/yr
djfa
vgT
(C
)
Trends from 1916-1997
Effects due toprecip trends
only
b) Max Accumulation c) 90 % Melta) 10 % Accumulation
Change in Date
Change in Date
Change in Date
Change in Date
DJF
Tem
p (C
)
Change in Date
DJF
Tem
p (C
)
Change in Date
DJF
Tem
p (C
)
Change in Date Change in Date
DJF
Tem
p (C
)
Change in Date
DJF
Tem
p (C
)
DJF
Tem
p (C
)
Change in Date Change in Date
DJF
Tem
p (C
)
Change in Date
DJF
Tem
p (C
)
DJF
Tem
p (C
)
Change in Date Change in Date
DJF
Tem
p (C
)
Change in Date
DJF
Tem
p (C
)
DJF
Tem
p (C
)
b) Max Accum. c) 90 % Melta) 10 % Accum.
Effects ofTemperatureonly
Effects ofPrecipitationonly
Effects ofTemperatureandPrecipitation
20th Century Climate Change Impacts in the Cascades
Elevation (m)
Cascades Sub Domain
0
100
200
300
400
500
600
700
oct
nov
dec
jan
feb
mar ap
r
may jun jul
aug
sep
Are
a A
ve
rag
e W
ate
r
(de
pth
in m
m)
precipitation
swe
runoff+baseflow
soil storage
evapotranspiration
Monthly Water Balance for the Washington Cascades
~1.8 trillion gallons
0
100
200
300
400
500
600
1Wat
er B
alan
ce f
rom
Ap
ril-
Sep
tem
ber
(dep
th in
mm
) precipitation
snowmelt
soil drainage
streamflow
ET
33%45%
22%
58%
42%
InputsOutputs
WA Cascades Water Balance from April-September1916-1974
0
100
200
300
400
500
600
1Wat
er B
alan
ce f
rom
Ap
ril-
Sep
tem
ber
(dep
th in
mm
) precipitation
snowmelt
soil drainage
streamflow
ET
38%39%
23%
56%
44%
InputsOutputs
WA Cascades Water Balance from April-September1975-1995
y = -3.3822x + 365.25
0
100
200
300
400
500
600
19
50
19
53
19
56
19
59
19
62
19
65
19
68
19
71
19
74
19
77
19
80
19
83
19
86
19
89
19
92
19
95
1-Apr
Linear (1-Apr)
y = -1.6073x + 319.11
0
50
100
150
200
250
300
350
400
450
19
50
19
53
19
56
19
59
19
62
19
65
19
68
19
71
19
74
19
77
19
80
19
83
19
86
19
89
19
92
19
95
1-Apr
Linear (1-Apr)
y = -1.7927x + 337.32
0
50
100
150
200
250
300
350
400
450
500
19
50
19
53
19
56
19
59
19
62
19
65
19
68
19
71
19
74
19
77
19
80
19
83
19
86
19
89
19
92
19
95
1-Apr
Linear (1-Apr)
Trends in Simulated Average APR 1 SWE for the Cascades in WA and OR (1950-1995)
Effects of TMP and PCP -54%
Effects of TMP -26% Effects of PCP -28%
SW
E (
mm
)
SW
E (
mm
)
y = -0.7939x + 319.540
100
200
300
400
500
600
1916
1921
1926
1931
1936
1941
1946
1951
1956
1961
1966
1971
1976
1981
1986
1991
1-Apr
Linear (1-Apr)
y = -0.7284x + 319.09
0
50
100
150
200
250
300
350
400
450
500
1916
1921
1926
1931
1936
1941
1946
1951
1956
1961
1966
1971
1976
1981
1986
1991
1-Apr
Linear (1-Apr)
y = -0.0896x + 291.69
0
50
100
150
200
250
300
350
400
450
500
1916
1921
1926
1931
1936
1941
1946
1951
1956
1961
1966
1971
1976
1981
1986
1991
1-Apr
Linear (1-Apr)
Effects of TMP and PCP -22%
Effects of TMP -20% Effects of PCP -2.5%
Trends in Simulated Average APR 1 SWE for the Cascades in WA and OR (1916-1995)
SW
E (
mm
)
SW
E (
mm
)
Cedar River: -30.7%
y = -0.0020x + 4.3416
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
1945 1955 1965 1975 1985 1995 2005
May
-Sep
t fr
acti
on
of
ann
ual
flo
w
May-Sept frac
Linear (May-Septfrac)
SFTolt River: -15.7%
y = -0.0010x + 2.2890
0
0.1
0.2
0.3
0.4
0.5
0.6
1945 1955 1965 1975 1985 1995 2005
May
-Sep
t fr
acti
on
of
ann
ual
flo
w
May-Sept frac
Linear (May-Septfrac)
Summer Water Availability is Declining
55 years
Figures courtesy of Matt Wiley and Richard Palmer at CEE, UW
20th Century Climate Change Impacts in the Snake River Basin
y = 0.0918x + 145.86
0
50
100
150
200
250
300
1916
1921
1926
1931
1936
1941
1946
1951
1956
1961
1966
1971
1976
1981
1986
1991
Ba
sin
Av
era
ge
SW
E (
mm
)
1-Apr
Linear (1-Apr)
Effects to SWE Upstream of Milner
y = 0.0004x + 0.4156
0.3
0.4
0.5
0.619
16
1921
1926
1931
1936
1941
1946
1951
1956
1961
1966
1971
1976
1981
1986
1991
1996
VIC
OBS
Linear (VIC)
Linear (OBS)
Simulated and Observed Natural Streamflow for Snake River at Milner
Fra
ctio
n of
Ann
ual F
low
fro
m J
une-
Sep
t
Dworshak
y = -0.0006x + 0.506
0.3
0.4
0.5
0.6
0.7
0.8
streamflow
Linear (streamflow)
Simulated Natural Streamflow for N. Fork Clearwater at Dworshak Dam
Fra
ctio
n of
Ann
ual F
low
fro
m J
une-
Sep
t
-10%In 82 yrs
Boise
y = -0.0003x + 0.2951
0.2
0.3
0.4
0.5
1916
1921
1926
1931
1936
1941
1946
1951
1956
1961
1966
1971
1976
1981
1986
1991
1996
2001
streamflow
Linear (streamflow)
Simulated Natural Streamflow for Boise River at Boise
Fra
ctio
n of
Ann
ual F
low
fro
m J
une-
Sep
t
-9.4%In 88 yrs
Fine Scale Comparison Between VIC and April 1 Snow course Observations
a) b) c)
d) e) f)
Pictures fo all 1144 sites available at:
ftp://ftp.atmos.washington.edu/philip/VICsnowbands_obs.ps
Conclusions
The Western US is experiencing large losses of SWE in sensitive areas (such as the Cascade mountain range) due to observed regional warming.
Without precipitation trends, essentially the entire mountain west would be experiencing declines in April 1 SWE due to large-scale warming.
Precipitation trends remain the major driver in areas with cold winter temperatures.
Precipitation trends seem to be most strongly associated with regionally-specific decadal-scale climate variability. A consistent global warming signal for precipitation across the West is not apparent.
Decadal variability is apparently not a good explanation for losses of snowpack associated with temperature trends. (Any period paired with 1977-1997 will show negative trends in SWE associated with temperature).
These results are consistent with the broad features of many global warming scenarios—i.e. rapid warming since the mid 1970s, modest increases in winter precipitation, streamflow timing shifts.