Dennis P. LettenmaierAlan F. Hamlet
JISAO Climate Impacts Group and the Department of Civil and Environmental
EngineeringUniversity of Washington
July, 2001
Effects of Climate Change on the Hydrology and Water Resources of the
PNW and Columbia River Basin
Elevation (m)
Areas with December temperaturesnear freezing
Topography of the Pacific Northwest
Annual PNW Precipitation
(mm)
WinterPrecipitation
SummerPrecipitation
(mm)
0.0
0.5
1.0
1.5
2.0
2.5
3.0
10 11 12 1 2 3 4 5 6 7 8 9
Month
No
rmal
ized
Str
eam
flow
SnowDominated
Transient Snow
Rain Dominated
Hydrologic Characteristics of PNW Rivers
Temperature warms,precipitation unaltered:
•Streamflow timing is altered• Annual volume stays about the same
Precipitation increases,temperature unaltered:
•Streamflow timing stays about the same•Annual volume is altered
Sensitivity of Snowmelt and Transient Riversto Changes in Temperature and Precipitation
0
100000
200000
300000
400000
500000
600000
700000
800000
900000
19
73
19
73
19
73
19
73
19
73
19
73
19
74
19
74
19
74
19
74
19
74
19
74
Water Year
Flo
w (
cfs
)
0
100000
200000
300000
400000
500000
600000
700000
800000
900000
19
73
19
73
19
73
19
73
19
73
19
73
19
74
19
74
19
74
19
74
19
74
19
74
Water Year
Flo
w (
cfs
)
Historic Analogues for the Effects of Climate Change
Ollalie Meadows (3700 ft elevation) WY 1995 Near Normal Precipitation Near Normal Temperatures
normal precipitation
normal snowpack
Normal Conditions
Ollalie Meadows (3700 ft elevation) WY 1992 Near Normal Precipitation Warm Temperatures ( + 3.5 F)
normal precipitation
normal snowpack
Unusually Warm Year
0
200
400
600
800
1000
1200
Oct
Nov
Dec Jan
Feb
Mar
Apr
May Jun
Jul
Aug
Sep
Flo
w (
cfs)
1992
avg
0
100000
200000
300000
400000
500000
600000
Oct
Nov
Dec Jan
Feb
Mar
Apr
May Jun
Jul
Aug
Sep
Flo
w (
cfs)
1992
avg
Cedar RiverWestern Cascades
(caused predominantly by warm temperatures)
Columbia Riverat The Dalles
(caused both by warm temperatures and decreased precipitation)
Effect of 1992 Winter Climate on Two PNW Rivers
Quantifying and Evaluating the Hydrologic Impacts of Climate Change
ColSimReservoir
Model
VICHydrology Model
Changes in Mean Temperature and
Precipitation from GCMs
Climate Change Scenarios 2020s
Climate Change Scenarios 2040s
The main impact: less snow
April 1
Columbia
Basin
Snow
Extent
Snow Accumulation and Ablation
0
20
40
60
80
100
120
140
160
180
200
oct nov dec jan feb mar apr may jun jul aug sep
Ba
sin
Ave
rag
e S
no
w W
ate
r E
qu
iva
len
t (m
m)
Base
HC 2025
MPI 2025
HC 2045
MPI 2045
Columbia Basin Average Snow Water EquivalentHadCM2 (Warm/Wet) and ECHAM4 (Warm/Dry) Scenarios
Conclusion:Both Warm/Wet and Warm/Dry scenarios result in reduced SWE
DALLES
0
100000
200000
300000
400000
500000
600000
oct
dec
feb
apr
jun
aug
Ave
rag
e F
low
(cf
s)
Base
comp 2020
Columbia River at The Dalles 2020s “Middle-of-the-Road” Scenario
DALLES
0
100000
200000
300000
400000
500000
600000
oct
dec
feb
apr
jun
aug
Ave
rag
e F
low
(cf
s)
Base
comp 2040
Columbia River at The Dalles 2040s “Middle-of-the-Road” Scenario
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
Effects to the Cedar River (Seattle Water Supply)for “Middle-of-the-Road” Scenarios
65
70
75
80
85
90
95
100
Flo
od C
ontr
ol
Firm
Ene
rgy
Non
-Firm
Ene
rgy
Sna
ke F
ish
Flo
ws
Mai
n S
tem
Fis
h F
low
s
Sna
ke Ir
rigat
ion
Lake
Roo
seve
lt R
ecr.
Re
liab
ility
of
Ob
ject
ive
(%
)
Current Climate
2020s Scenario
2040s Scenario
Simulated Reliability of Water Resources Objectivesfor “Middle-of-the-Road” Scenarios
Quantifying Uncertainties
Changes to PNW Annual Temperature(High, Medium, Low)
Changes to PNW Winter Precipitation (High, Medium, Low)
The DALLES
0
100000
200000
300000
400000
500000
600000
oct
dec
feb
apr
jun
aug
Av
era
ge
Flo
w (
cfs
)
20th CenturyClimate
High (PCM)
Low (ECHAM4)
Middle of theRoad
Range of Uncertainties in Summer Streamflow Simulations at The Dalles for 2040s Scenarios
50
60
70
80
90
100F
irm E
nerg
y
No
n-F
irm E
nerg
y
Gra
nd C
oul
ee
Re
cre
atio
n
Lo
we
r G
rani
te F
ish
Flo
w
McN
ary
Fis
h F
low
Sna
ke I
rrig
atio
n
Sna
ke R
ive
r N
avig
atio
n
Flo
od
Co
ntro
l
Current Climate
ECHAM4 2040's
PCM 2040's
Range of Uncertainty in Water Resources Sensitivity for 2040s Scenarios
Frequency of Drought in the Columbia River Comparable to Water Year 1992
(data from 1962-1997)
0
2
4
6
8
10
12
14
16
Base Mean2020s
Mean2040s
ECHAM42040s
PCM2040s
Scenario
Nu
mb
er
of
Oc
cu
ren
ce
s
x 2
x 4.7
x 1.3 x 1.3
•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•Very limited use of available streamflow forecasts incorporating climate change information•Changes in intra-regional water availability (e.g. different changes in Canada and US) may disrupt existing management framework and agreements
Areas of Concern for Water Management
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 mid-winter 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
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).
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.
Conclusions (cont.)