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ASSESSING POTENTIAL IMPACTS OF
CLIMATE CHANGE ON WATER
RESOURCES:
THREE WESTERN U.S. CASE STUDIES
Dennis P. Lettenmaier
Department of Civil and Environmental Engineering
University of Washington
Center for Streamside Studies and Center for Urban Water Resources
Management
Annual Review of Research
February 6, 2003
Humans are altering
atmospheric
composition
Natural Climate Influence
Human Climate Influence
All Climate Influences
Trends in timing of spring snowmelt (1948-2000)
+20d later
–20d earlier
Courtesy of Mike Dettinger, Iris Stewart, Dan Cayan
Trends in snowpack
Climate
Scenarios
Global climate
simulations, next
~100 yrs
Hydrologic
Model (VIC)
Natural
Streamflow
Downscaling
Delta
Precip,
Temp
Performance
Measures
Reliability
of System
Objectives
Reservoir
Model
DamReleases,
Regulated
Streamflow
Accelerated
Climate Prediction
Initiative (ACPI) –
NCAR/DOE
Parallel Climate
Model (PCM) grid
over western U.S.
Climate Change Scenarios
PCM Simulations (~ 3 degrees lat-long)
Historical
B06.22 (greenhouse CO2+aerosols forcing)
1870-2000
Climate Control
B06.45 (CO2+aerosols at 1995 levels)
1995-2048
Climate Change
Climate Change
Climate Change
B06.44 (BAU6, future scenario forcing)
B06.46 (BAU6, future scenario forcing)
B06.47 (BAU6, future scenario forcing)
1995-2099
1995-2099
1995-2099
PNNL Regional Climate Model (RCM)
Simulations (~ ¾ degree lat-long)
Climate Control
B06.45 derived-subset
1995-2015
Climate Change
B06.44 derived-subset
2040-2060
Downscaling
monthly PCM
anomaly (T42)
interpolated to
VIC scale
VIC-scale
monthly simulation
observed
mean fields
(1/8-1/4 degree)
Coupled LandAtmosphere-Ocean
General Circulation
Model
Hydrology Model
Reservoir
Model
BAU 3-run average
historical (1950-99)
control (2000-2048)
PCM
Business-as-Usual
scenarios
Columbia River Basin
(Basin Averages)
PCM
Business-AsUsual
Mean
Monthly
Hydrographs
Columbia
River Basin
@ The Dalles,
OR
1
month
12
1
month
12
Period 3
Period 2
Period 1
Percent of Control Run Climate
2040-2069
140
120
PCM Control Climate and
Current Operations
100
PCM Projected Climate
and Current Operations
PCM Projected Climate
with Adaptive Management
80
60
Firm
Hydropower
Annual Flow
Deficit at
McNary
Percent of Control Run Climate
2070-2098
140
PCM Control Climate and
Current Operations
120
PCM Projected Climate
and Current Operations
100
PCM Projected Climate
with Adaptive
Management
80
60
Firm
Hydropower
Annual Flow
Deficit at
McNary
BAU 3-run average
historical (1950-99)
control (2000-2048)
PCM
Business-as-Usual
scenarios
California
(Basin Average)
PCM
Business-as-Usual Scenarios
Snowpack Changes
California
April 1 SWE
PCM
Business-AsUsual
Mean
Monthly
Hydrographs
Shasta
Reservoir
Inflows
1
month
12
1
month
12
Central Valley Water Year Type Occurrence
Percent Given WY Type
0.6
hist (1906-2000)
0.5
2020s
2050s
2090s
0.4
0.3
0.2
0.1
0.0
Critically Dry
Dry
Below Normal
Water Year Type
Above Normal
Wet
PCM Projected Colorado R. Temperature
Timeseries
Annual Average
ctrl. avg.
hist. avg.
Period 1 2010-2039
Period 2 2040-2069
Period 3 2070-2098
Annual Average Hydrograph
Simulated Historic (1950-1999)
Control (static 1995 climate)
Period 1 (2010-2039)
Period 2 (2040-2069)
Period 3 (2070-2098)
Natural Flow at Lee Ferry, AZ
Natural Flow at Lee Ferry Stream Gage
30
Annual Flow (BCM)
25
allocated
20.3 BCM
20
15
Currently used
16.3 BCM
10
5
0
1900
1910
1920
1930
Annual Flow
1940
1950
10 Year Average
1960
1970
1980
Running Average
1990
2000
Annual Releases to the Lower Basin
Figure 9
14
1.2
Average Annual Release to Lower Basin (BCM/YR)
Probability release to Lower Basin meets or exceeds target (probability)
12
1
target release
10
8
0.6
6
0.4
4
0.2
2
0
0
Historical
Control
Period 1
Period 2
Period 3
Probability
BCM / YR.
0.8
Annual Releases to Mexico
Figure 10
1.2
Average Annual Release to Mexico
(BCM/YR)
3
Probability release to Mexico meets or
exceeds target (probability)
BCM / YR.
2.5
1
0.8
2
target release
0.6
1.5
0.4
1
0.2
0.5
0
0
Historical
Control
Period 1
Period 2
Period 3
Probability
3.5
Annual Hydropower Production
Figure 12
18000
Minimum
16000
Average
Energy, GW - hr
14000
Maximum
12000
10000
8000
6000
4000
2000
0
Historical
Control
Period 1
Period 2
Period 3
Conclusions and Comparative analysis
• 1) Columbia River reservoir system primarily provides within-year
storage (total storage/mean flow ~ 0.3). California is intermediate (~
0.3), Colorado is an over-year system (~4)
• 2) Climate sensitivities in Columbia basin are dominated by
seasonality shifts in streamflow, and may even be beneficial for
hydropower. However, fish flow targets would be difficult to meet
under altered climate, and mitigation by altered operation is
essentially impossible.
• 3) California system operation is dominated by water supply (mostly
ag), reliability of which would be reduced significantly by a
combination of seaonality shifts and reduced (annual) volumes.
Partial mitigation by altered operations is possible, but complicated
by flood issues.
• 4) Colorado system is sensitive primarily to annual streamflow
volumes. Low runoff ratio makes the system highly sensitive to
modest changes in precipitation (in winter, esp, in headwaters).
Sensitivity to altered operations is modest, and mitigation possibilities
by increased storage are nil (even if otherwise feasible).