dennis p. lettenmaier department of civil and environmental engineering university of washington
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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 EngineeringUniversity of Washington
Department of Hydrology and Water ResourcesUniversity of Arizona
December 4, 2002
Outline of this talk
1) Climate variability and change context
2) Prediction and assessment approach
3) Accelerated Climate Prediction Initiative (ACPI)
4) Hydrology and water management implications for Columbia, Sacramento-San Joaquin, and Colorado River basins
5) Conclusions and comparative analysis
1) Climate variability and change context
Humans are altering atmospheric composition
The earth is warming -- abruptly
Natural Climate Influence Human Climate Influence
All Climate Influences
Temperature trends in the PNW over the instrumental record
• Almost every station shows warming (filled circles)
• Urbanization not a major source of warming
Trends in timing of spring snowmelt (1948-2000)
Courtesy of Mike Dettinger, Iris Stewart, Dan Cayan
+20d later–20d earlier
Trends in snowpack
Northwest warming
44
45
46
47
48
49
50
51
52
53
54
1900
s
1920
s
1940
s
1960
s
1980
s
2000
s
2020
s
2040
s
Deg
rees
F
warmest scenario
average
coolest scenario
observed
CGCM1
2) Prediction and assessment approach
Climate Scenarios
Global climate simulations, next ~100 yrs
Downscaling
Delta Precip,Temp
HydrologicModel (VIC)
Natural Streamflow
ReservoirModel
DamReleases,Regulated
Streamflow
PerformanceMeasures
Reliability of System Objectives
ReservoirModel
Hydrology Model
Coupled Land-Atmosphere-Ocean General Circulation
Model
Accelerated Climate Prediction Initiative (ACPI) – NCAR/DOE Parallel Climate Model (PCM) grid over western U.S.
Bias Correction and Downscaling Approach
climate model scenariometeorological outputs
hydrologic model inputs
snowpackrunoffstreamflow
• 1/8-1/4 degree resolution• daily P, Tmin, Tmax
•2.8 (T42)/0.5 degree resolution•monthly total P, avg. T
Bias Correction
from NCDC observations
from PCM historical runraw climate scenario
bias-corrected climate scenario
month mmonth m
Note: future scenario temperature trend (relative to control run) removed before, and replaced after, bias-correction step.
Downscaling
observed mean fields
(1/8-1/4 degree)
monthly PCManomaly (T42)
VIC-scale monthly simulation
interpolated to VIC scale
Overview of ColSim Reservoir Model
Physical Systemof Damsand Reservoirs
Reservoir Operating Policies
Reservoir StorageRegulated StreamflowFlood ControlEnergy ProductionIrrigation ConsumptionStreamflow Augmentation
0100000200000300000400000500000600000700000800000900000
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
Flow
(cfs
)
Streamflow Time Series
Dam Operations in ColSim
Storage Dams
Run-of-River Dams
0
100000
200000
300000
400000
500000
600000
Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep
Month
Avg
Str
eam
flow
(cf
s)
0
100000
200000
300000
400000
500000
600000
Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep
Month
Avg
Str
eam
flow
(cf
s) Virgin Regulated
Flow In=Flow out + Energy
H
Inflow
Run of River Reservoirs (inflow=outflow + energy)
Inflow
Inflow
Inflow
Inflow
Inflow
Storage ReservoirsReleases Depend on:•Storage and Inflow•Rule Curves (streamflow forecasts)•Flood Control Requirements•Energy Requirements•Minimum Flow Requirements•System Flow Requirements
System Checkpoint
Consumptive use
Consumptive use
Inflow +
ColSim
3) Accelerated Climate Prediction Initiative (ACPI)
GCM grid mesh over western U.S. (NCAR/DOE Parallel Climate Model at ~ 2.8 degrees lat-long)
Climate Change Scenarios
Historical B06.22 (greenhouse CO2+aerosols forcing) 1870-2000
Climate Control B06.45 (CO2+aerosols at 1995 levels) 1995-2048
Climate Change B06.44 (BAU6, future scenario forcing) 1995-2099 Climate Change B06.46 (BAU6, future scenario forcing) 1995-2099 Climate Change B06.47 (BAU6, future scenario forcing) 1995-2099
Climate Control B06.45 derived-subset 1995-2015
Climate Change B06.44 derived-subset 2040-2060
PCM Simulations (~ 3 degrees lat-long)
PNNL Regional Climate Model (RCM) Simulations (~ ¾ degree lat-long)
Future streamflows
• 3 ensembles averaged
• summarized into 3 periods;» Period 1 2010 - 2039
» Period 2 2040 - 2070
» Period 3 2070 - 2098
Regional Climate Model (RCM) grid and hydrologic model domains
ACPI: PCM-climate change scenarios, historic simulation v air temperature observations
ACPI: PCM-climate change scenarios, historic simulation v precipitation observations
4a) Hydrology and water management implications: Columbia River Basin
PCM Business-as-Usual scenarios
Columbia River Basin(Basin Averages)
control (2000-2048)
historical (1950-99)
BAU 3-run average
RCM Business-as-Usual scenarios
Columbia River Basin(Basin Averages)
control (2000-2048)
historical (1950-99)
PCM BAU B06.44
RCM BAU B06.44
PCMBusiness-As-Usual
Mean Monthly
Hydrographs
Columbia River Basin@ The Dalles, OR
1 month 12 1 month 12
CRB Operation Alternative 1 (early refill)
15,000,000
20,000,000
25,000,000
30,000,000
35,000,000
40,000,000
45,000,000
50,000,000
55,000,000
O N D J F M A M J J A S
To
tal
En
d o
f M
on
th S
yste
m S
tora
ge
(acr
e-fe
et)
Max Storage
Control
Base Climate Change
Change (Alt. 1)
Dead Pool
CRB Operation Alternative 2 (reduce flood storage by 20%)
15,000,000
20,000,000
25,000,000
30,000,000
35,000,000
40,000,000
45,000,000
50,000,000
55,000,000
O N D J F M A M J J A S
En
d o
f M
on
th T
ota
l S
ys
tem
Sto
rag
e (
ac
re-f
ee
t)
Max Storage
Control
Base Climate Change
Change (Alt. 2)
Dead Pool
Columbia River Basin Water Resource Sensitivity to PCM Climate Change Scenarios
0%
20%
40%
60%
80%
100%
120%
Portland-Vancouver
Spring FloodControl
Reliability
Portland-Vancouver
Winter FloodControl
Reliability
Autumn FirmPower
Reliability(November)
% of ControlHydropower
Revenues
McNaryInstream
TargetReliability
(April-August)
Middle SnakeAgriculturalWithdrawalReliability
Grand CouleeRecreationReliability
Rel
iab
ility
(%
, mo
nth
ly b
ased
)
Control
Period 1
Period 2
Period 3
RCM
A v e r a g e M o n t h ly D e f i c i t a t t h e M c N a r y D a m T a r g e t ( c f s )
M o n th ly R e l i a b i l i t y a t t h e M c N a r y D a m T a r g e t
Per
iod
1
-
20,000
40,000
60,000
80,000
100,000
120,000
Apr May Jun Jul Aug
Control
Current Operations
Refill 2 w eeks earlier
Refill 1 month earlier
2040-2069
60
80
100
120
140
FirmHydropower
Annual FlowDeficit atMcNary
Pe
rce
nt
of
Co
ntr
ol
Ru
n C
lim
ate
PCM Control Climate andCurrent Operations
PCM Projected Climateand Current Operations
PCM Projected Climatewith Adaptive Management
2070-2098
60
80
100
120
140
FirmHydropower
Annual FlowDeficit atMcNary
Perc
en
t o
f C
on
tro
l R
un
Cli
mate
PCM Control Climate andCurrent Operations
PCM Projected Climateand Current Operations
PCM Projected Climatewith AdaptiveManagement
Per
iod
1
Per
iod
2
Per
iod
3
4a) Hydrology and water management implications: Sacramento-San Joaquin River Basin
PCM Business-as-Usual scenarios
California(Basin Average)
control (2000-2048)
historical (1950-99)
BAU 3-run average
PCM Business-as-Usual Scenarios
Snowpack ChangesCaliforniaApril 1 SWE
PCMBusiness-As-Usual
Mean MonthlyHydrographs
Shasta Reservoir Inflows
1 month 12 1 month 12
Trinity Lake Storage: 2448
taf
Lake Shasta Storage: 4552 taf
Lake OrovilleStorage: 3538 taf
Folsom Lake Storage: 977 taf
WhiskeytownStorage: 241 taf
Sacramento River Basin
Trinity
Whiskeytown
Shasta
Oroville (SWP)
Folsom
Clear Creek
American River
Feather River
Trinity River
Sac
ram
ento
Riv
er
Dam
Power Plant
River
Transfer
Delta
Delta & San Joaquin R Basin
Dam
Power Plant
River/Canal
Transfer
Eastman, Hensley, & Millerton
New Don Pedro & McClure
Delta
New Hogan
Pardee & Camanche
Stanislaus River
Tuolumne & Merced Rivers
Delta Outflow
Mokelumne River
Calaveras River
San
Joaquin
River
Pardee/CamancheReservoir
Storage: 615 taf
New Melones ResStorage: 2420 tafDon Pedro/McClureStorage: 3055 taf
Millerton LakeStorage: 761 taf
Sacramento-San Joaquin Delta
Area: 1200 mi2
DeltaSan Luis Reservoir
CVP: 971 tafSWP: 1070 taf
New Melones
San Luis
Central Valley Water Year Type Occurrence
0.0
0.1
0.2
0.3
0.4
0.5
0.6
Critically Dry Dry Below Normal Above Normal Wet
Water Year Type
Per
cen
t G
iven
WY
Typ
e
hist (1906-2000) 2020s 2050s 2090s
Storage Decreases• Sacramento
Range: 5 - 10 %Mean: 8 %
• San Joaquin Range: 7 - 14 %Mean: 11 %
Current Climate vs. Projected Climate
Current Climate vs. Projected Climate
Central Valley Hydropower Production
200000
400000
600000
800000
1000000
1200000
1400000
OctNov
Dec Jan
Feb Mar Apr
May Ju
nJu
lAug
Sep
Meg
awat
t-H
ou
rs
Ctrl mean
2000-2019
2020-2039
2040-2059
2060-2079
2080-2098
Hydropower Losses• Central Valley
Range: 3 - 18 %Mean: 9 %
• Sacramento System Range: 3 – 19 %Mean: 9%
• San Joaquin System Range: 16 – 63 %Mean: 28%
4a) Hydrology and water management implications: Colorado River basin
Timeseries Annual Average
Period 1 2010-2039 Period 2 2040-2069 Period 3 2070-2098
hist. avg.
ctrl. avg.
PCM Projected Colorado R. Temperature
hist. avg.
ctrl. avg.
PCM Projected Colorado R. Precipitation
Timeseries Annual Average
Period 1 2010-2039 Period 2 2040-2069 Period 3 2070-2098
Annual Average Hydrograph
Simulated Historic (1950-1999) Period 1 (2010-2039)Control (static 1995 climate) Period 2 (2040-2069)
Period 3 (2070-2098)
Projected Spatial Change in Runoff
90 %86 %82 %83 %
April 1 Snow Water Equivalent
Natural Flow at Lee Ferry, AZ
Currently used 16.3 BCM
allocated20.3 BCM
Storage ReservoirsRun of River Reservoirs
CRRM
• Basin storage aggregated into 4 storage reservoirs
– Lake Powell and Lake Mead have 85% of basin storage
• Reservoir evaporation = f(reservoir surface area, mean monthly temperature)
• Hydropower = f(release, reservoir elevation)
• Monthly timestep
• Historic Streamflows to Validate
• Projected Inflows to assess future performance of system
Water Management Model (CRRM)
• Multi Species Conservation Program year 2000 demands– upper basin 5.4 BCM
– lower basin 9.3 BCM
– Mexico 1.8 BCM
• Minimum Annual Release from Glen Canyon Dam of 10.8 BCM
• Minimum Annual Release from Imperial Dam of 1.8 BCM
Total Basin Storage
Annual Releases to the Lower Basin
target release
Annual Releases to Mexico
target release
Annual Hydropower Production
Uncontrolled Spills
Deliveries to CAP & MWD
Precipitation
Annual Average Change (mm/yr) in:
Evapo-transpiration
Runoff
mm / yr.
Colorado River Basin Annual Average
Precipitation (mm/yr)
(mm/yr)
NE cell
X X
X
SW cell
NW cell
5) 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).
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