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Effects of Climate Change on the
Hydrology and Water Resources of the
PNW and the Columbia River Basin
JISAO Climate Impacts Group and the
Department of Civil and Environmental
Engineering
University of Washington
January, 2003
Alan F. Hamlet
Dennis P. Lettenmaier
Topography of the Pacific Northwest
Elevation (m)
Areas with December
temperatures
near freezing
Annual PNW Precipitation
(mm)
(mm)
Winter
Precipitation
Summer
Precipitation
Hydrologic Characteristics of PNW Rivers
Normalized Streamflow
3.0
2.5
Snow
Dominated
2.0
Transient Snow
1.5
Rain Dominated
1.0
0.5
0.0
10 11 12
1
2
3
4
Month
5
6
7
8
9
Sensitivity of Snowmelt and Transient Rivers
to Changes in Temperature and Precipitation
900000
700000
600000
500000
400000
300000
200000
100000
1974
1974
1974
1974
1974
1974
1974
1974
1974
1974
1973
1973
1973
1973
1973
0
1973
•Streamflow timing is altered
• Annual volume stays about
the same
800000
Flow (cfs)
Temperature warms,
precipitation unaltered:
Water Year
900000
800000
600000
500000
400000
300000
200000
100000
1974
1974
1973
1973
1973
1973
1973
0
1973
•Streamflow timing stays about the same
•Annual volume is altered
700000
Flow (cfs)
Precipitation increases,
temperature unaltered:
Water Year
Historic Analogues for the Effects
of Climate Change
Normal Conditions
Ollalie Meadows (3700 ft elevation) WY 1995
Near Normal Precipitation Near Normal Temperatures
normal precipitation
normal snowpack
Unusually Warm Year
Ollalie Meadows (3700 ft elevation) WY 1992
Near Normal Precipitation Warm Temperatures ( + 3.5 F)
normal precipitation
normal snowpack
Effect of 1992 Winter Climate on Two PNW Rivers
1200
1000
Flow (cfs)
(caused predominantly by
warm temperatures)
800
1992
600
avg
400
200
Sep
Aug
Jul
Jun
May
Apr
Mar
Feb
Dec
Oct
Jan
0
Nov
Cedar River
Western Cascades
600000
400000
1992
300000
avg
200000
100000
Sep
Aug
Jul
Jun
May
Apr
Mar
Feb
Jan
Dec
Nov
0
Oct
(caused both by warm
temperatures and
decreased precipitation)
500000
Flow (cfs)
Columbia River
at The Dalles
Quantifying and Evaluating the Hydrologic
Impacts of Climate Change
Changes in Mean
Temperature and
Precipitation from
GCMs
VIC
Hydrology Model
ColSim
Reservoir
Model
Climate Change Scenarios 2020s
Climate Change Scenarios 2040s
The main impact: less snow
April 1 Snowpack (mm)
Current Climate
2020s
2040s
PNW Average Monthly Snowpack
Composite “Middle of the Road” Scenarios
Average Snow Water Equivalent (mm)
250
Current Climate
comp 2020s
200
comp 2040s
150
100
50
0
oct
nov
dec
jan
feb
mar
apr
may
jun
jul
aug
sep
Columbia River at The Dalles for “Middle-of-the-Road” Scenarios
DALLES
500000
400000
Base
300000
2020s
2040s
200000
100000
aug
jun
apr
feb
dec
0
oct
Average Flow (cfs)
600000
Effects to the Cedar River (Seattle Water Supply)
for “Middle-of-the-Road” Scenarios
9000
8000
6000
Simulated 20th
Century Climate
2020s Climate
Change Scenario
2040s Climate
Change Scenario
5000
4000
3000
2000
1000
Date
9/2
8/5
7/8
6/10
5/13
4/15
3/18
2/18
1/21
12/24
11/26
10/29
0
10/1
Inflow (acre-ft)
7000
Spatial Effects
Corra Linn
Chief Joseph
Ice Harbor
The Dalles
Effects of Basin Location
20000
aug
100000
50000
0
20000
aug
jun
apr
feb
dec
0
300000
comp 2040
comp 2020
200000
100000
0
aug
comp 2020
40000
Base
jun
comp 2040
60000
400000
apr
Base
80000
500000
dec
100000
600000
oct
120000
Average Flow (cfs)
DALLES
140000
oct
Average Flow (cfs)
ICE HARBOR
feb
jun
apr
feb
dec
0
comp 2020
aug
comp 2020
40000
comp 2040
150000
jun
60000
Base
200000
apr
comp 2040
250000
feb
Base
300000
dec
80000
350000
oct
100000
Average Flow (cfs)
CHIEF JOSEPH
120000
oct
Average Flow (cfs)
CORRA LINN
Water Resources in the Columbia River Basin
System objectives affected by winter flows
Winter hydropower production (PNW demand)
System objectives affected by summer flows
Flood control
Summer hydropower production (California demand)
Irrigation
Instream flow for fish
Recreation
100
95
90
Current Climate
85
2020s Scenario
80
2040s Scenario
75
70
Lake Roosevelt Recr.
Snake Irrigation
Main Stem Fish Flows
Snake Fish Flows
Non-Firm Energy
Firm Energy
65
Flood Control
Reliability of Objective (%)
Simulated Reliability of Water Resources Objectives
for “Middle-of-the-Road” Scenarios
Quantifying Uncertainties
Range of Uncertainties in Summer Streamflow Simulations
at The Dalles for 2040s Scenarios
600000
500000
20th Century
Climate
400000
High (PCM)
300000
Low (ECHAM4)
200000
Middle of the
Road
100000
aug
jun
apr
feb
dec
0
oct
Average Flow (cfs)
The DALLES
Flood Control
Snake River Navigation
Snake Irrigation
McNary Fish Flow
Lower Granite Fish Flow
Grand Coulee Recreation
Non-Firm Energy
Firm Energy
Range of Uncertainty in Water Resources Sensitivity
for 2040s Scenarios
100
90
80
70
Current Climate
ECHAM4 2040's
PCM 2040's
60
50
Number of Occurences
Frequency of Drought Comparable to Water Year 1992 in the
Columbia River Basin (data from 1962-1997)
16
x 4.7
14
12
10
8
x2
6
x 1.3
4
x 1.3
2
0
Base
Mean
2020s
Mean
2040s
Scenario
ECHAM4
2040s
PCM
2040s
An Example of Water Management Tradeoffs
Associated with Adaptation
(from Payne et al. 2003)
Percent of Control Run Climate
Effects to Hydropower and Fish Flows
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
Effects to Hydropower and Fish Flows
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
Free Streamflow Scenarios for the PNW
http://www.ce.washington.edu/~hamleaf/climate_change_streamflows/CR_cc.htm
Areas of Concern for Water Management
•Limited reservoir storage is available, and there is little opportunity
to build more (storage/streamflow ratios are 10% to 30% in most
basins--vulnerable to timing shifts)
•Water systems are operated closer to their supply limits now than
in the past (effective management is more important)
•Use of historic streamflow record for long-range planning
•Use of statistical streamflow forecasting tools based on 30-year
streamflow record
•Inflexibility and fragmentation of water management institutions
and entities
•Different changes in Canada and US may disrupt existing
management framework and agreements
Conclusions
PNW hydrology is predominantly controlled by winter conditions in
the mountains. Warmer temperatures produce streamflow timing
changes in most PNW basins. Changes in precipitation produce
changes in streamflow volumes. Basins encompassing the midwinter snow line are most sensitive to warming.
The primary impact of warming in the PNW is loss of mountain
snowpack. For the scenarios investigated, both warm/wet and
warm/dry scenarios result in decreased snow water equivalent in the
Columbia basin.
Warmer temperatures generally results in higher winter flows, lower
summer flows, and earlier peak flows in spring
Effects to the Columbia water resources system are largely
associated with reduced reliability of system objectives affected by
summer streamflows (water supply, irrigation, summer hydropower,
instream flow).
Conclusions (cont.)
There are significant uncertainties regarding changes in
precipitation and the resulting intensity of reductions in summer
streamflows and increases in the frequency of droughts.
However, a consistent and robust result is that some reduction in
summer streamflow and increase in drought frequency is present in
all scenarios by the 2040s for the Columbia basin.
The greatest impacts to the Columbia system are for the warm/dry
scenarios, which produce the strongest reductions in summer
streamflows and the greatest increases in drought frequency.
The reductions in summer streamflows in these scenarios are likely
to exacerbate existing conflicts over water, the impacts of regional
growth, and weaknesses in infrastructure, water management
practice, and management institutions.