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.)