Alan F. HamletDennis P. Lettenmaier

Amy K. Snover

JISAO Center for Science in the Earth System Climate Impacts Group

and Department of Civil and Environmental EngineeringUniversity of Washington

April, 2003

Climate Change Streamflow Scenarios for Critical Period Water Planning Studies

Changing Awareness of Climate Change in the Water Management Community

~1985: Global warming? ~1995: Is global warming real?~1997: What are the expected impacts of

climate change for our region and our water system?

~2002: How do we include climate change and climate uncertainty in long term planning to reduce risks?

Current Climate 2020s 2040s

The primary impact pathway in the western US: less snow

Snow Water Equivalent (mm)

Columbia River at The Dalles for “Middle-of-the-Road” Scenarios

Columbia River at The Dalles

0

100000

200000

300000

400000

500000

600000

oct

dec

feb

apr

jun

aug

Ave

rag

e F

low

(cfs

)

Base

2020s

2040s

Inflow to Chester Morse Lake

0

1000

2000

3000

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6000

7000

8000

900010

/1

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6

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4

1/21

2/18

3/18

4/15

5/13

6/10 7/

8

8/5

9/2

Infl

ow

(ac

re-f

t)

Base

2020s

2040s

Effects to Moderate Elevation Basins in the Cascades

Project Motivation:

•Target existing planning processes at the watershed scale

•Make streamflow scenarios freely available to help reduce costs of including climate uncertainty in long-term planning

(Recommendations from regional stakeholders and policy makers attending a CIG sponsored climate change workshop Skamania, 2001)

Observed Streamflows

Planning Models

System Drivers

Critical Period Planning Methods for Water Studies

Columbia River at The Dalles

0100000200000300000400000500000600000700000800000

1925

1925

1925

1926

1926

1927

1927

1927

1928

1928

1929

1929

1930

1930

1930

1931

1931

1932

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1934

Observed Streamflows

Climate Change Scenarios

Planning Models

Long term planning for climate change may include a stronger emphasis on drought contingency planning, testing of preferred planning alternatives for robustness under various climate change scenarios, and increased flexibility and adaptation to climate and streamflow uncertainty.

Altered Streamflows

System Drivers

Incorporating Climate Change in Critical Period Planning

Project Goals:

•Create climate change streamflow scenarios that cover the same period of record and are numerically consistent with the historic record of streamflows traditionally used in water planning studies.

•Make these streamflow scenarios freely available on the web for a large number of river locations to facilitate the incorporation of climate change information into existing water planning efforts.

Choice of GCM Downscaling Methods for the Pilot Study

Although more sophisticated methods are also available, the “Delta” method of downscaling GCM results was chosen for the pilot applications.

•Good fit with producing alternate versions of the historic record used in critical period planning studies.

•Easy to understand and interpret (the project has an educational component).

•Captures much of the regional scale information from GCM simulations.

Precipitation Fraction, 2020s

0.5

0.75

1

1.25

1.5

1.75

J F M A M J J A S O N D

Frac

tion

hadCM2

hadCM3

PCM3

ECHAM4

mean

Delta T, 2020s

-1

0

1

2

3

4

5

J F M A M J J A S O N D

De

gre

es

C

hadCM2

hadCM3

PCM3

ECHAM4

mean

Delta T, 2040s

-1

0

1

2

3

4

5

J F M A M J J A S O N D

De

gre

es

C

hadCM2

hadCM3

PCM3

ECHAM4

mean

Precipitation Fraction, 2040s

0.5

0.75

1

1.25

1.5

1.75

J F M A M J J A S O N D

Fra

ctio

n

hadCM2

hadCM3

PCM3

ECHAM4

mean

Delta Method Climate Change Scenarios for the PNW

~ + 1.7 C ~ + 2.5 C

Somewhat wetter winters and perhaps somewhat dryer summers

ColSimReservoir

Model

VICHydrology Model

Changes in Mean Temperature and

Precipitation or Bias Corrected Output

from GCMs

Issues with Hydrologic Model Bias

Columbia River at The Dalles

0100000200000300000400000500000600000700000800000900000

1985

1985

1986

1987

1987

1988

1989

1989

1990

1991

1991

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1995

1995

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1999

Str

ea

mfl

ow

(cf

s)

VIC

Observed

Quantile-Based Bias Correction (Wood et al. 2002)

0

5000

10000

15000

20000

25000

30000

35000

0 0.2 0.4 0.6 0.8 1

Probability of Exceedence

Flo

w (

cfs)

obs

vic

VIC Input = 19000

Bias Corrected Output = 10000

Bias Correction Objectives:

Result: Bias corrected hydrologic simulations are quite consistent with observed streamflows in absolute value and climate change signals are translated without significant distortion.

Raw Bias Corrected

Bias Corrected Time Series Plot for the Current Climate

Bias Corrected Time Series Plot for the Composite 2040 Scenario

Web-Based Data Archive

http://www.ce.washington.edu/~hamleaf/climate_change_streamflows/CR_cc.htm

Goals and Objectives of Two Regional-Scale Pilot Studies in the Pacific Northwest

Northwest Power Planning Council:

Primarily focused on reliability of the Columbia River hydropower system. Study will use the GENESYS model.Preliminary results in John Fazio’s talk this afternoon.

Idaho Department of Water Resources:

Primarily focused on groundwater/surface water interactions, sustainability of irrigated agriculture in the Snake River

basin, groundwater/surface water interactions and water allocation amongst different users and uses.

Current Streamflow Routing Locations

Some Selected Results for the Snake River Basin

(Composite Scenarios)

Planned Project Extensions

•Extend the period of record of the data to 1928-1999.

•Extend the number of climate change scenarios and the downscaling methods used.

Summary and Conclusions

Water policy workshops (Skamania 2001) have highlighted the need to inject climate change information into existing river basin planning activities where possible and to provide access to free streamflow scenarios to help reduce costs.

Because most planning studies currently use a critical period framework, our project produces “adjusted” realizations of the historic streamflow record based on simulations from a physically based hydrologic model driven by simple climate change scenarios.

The methods are flexible and portable and can be used to create streamflow scenarios deriving from different climate model scenarios, different downscaling methods, or different hydrologic models.