alan f. hamlet se- yeun lee

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Effects of Climate Change on Natural and Regulated Flood Risks in the Skagit River Basin and Prospects for Adaptation Alan F. Hamlet Se-Yeun Lee Dept. of Civil and Env. Engineering, UW Skagit Climate Science Consortium (SC 2 ) Climate Impacts Group, UW

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Effects of Climate Change on Natural and Regulated Flood Risks in the Skagit River Basin and Prospects for Adaptation. Alan F. Hamlet Se- Yeun Lee . Dept. of Civil and Env . Engineering, UW Skagit Climate Science Consortium (SC 2 ) Climate Impacts Group, UW. - PowerPoint PPT Presentation

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Page 1: Alan  F.  Hamlet Se- Yeun  Lee

Effects of Climate Change on Natural and Regulated Flood Risks

in the Skagit River Basin and Prospects for Adaptation

Alan F. HamletSe-Yeun Lee

Dept. of Civil and Env. Engineering, UWSkagit Climate Science Consortium (SC2)Climate Impacts Group, UW

Page 2: Alan  F.  Hamlet Se- Yeun  Lee

Study Area : The Skagit River Basin

Ross dam on the Upper Skagit River and Upper Baker dam on the Baker River provide storage for flood control.

Inflows to Ross and Upper Baker dams are relatively small portion (less than 40 %) of the total flows in the lower Skagit River.

Page 3: Alan  F.  Hamlet Se- Yeun  Lee

Floodplain Development in the Skagit

Page 4: Alan  F.  Hamlet Se- Yeun  Lee

Mote, P.W. and E. P. Salathe Jr., 2010: Future climate in the Pacific Northwest, Climatic Change, DOI: 10.1007/s10584-010-9848-z

21st Century Climate Impacts for the Pacific Northwest Region

Page 5: Alan  F.  Hamlet Se- Yeun  Lee

Seasonal Precipitation Changes for the Pacific Northwest

Mote, P.W. and E. P. Salathe Jr., 2010: Future climate in the Pacific Northwest, Climatic Change, DOI: 10.1007/s10584-010-9848-z

Page 6: Alan  F.  Hamlet Se- Yeun  Lee

Warmer, wetter conditions are projected to substantially increase flood risks in the Skagit River Basin under natural (or unregulated) conditions (Tohver and Hamlet, 2010; Hamlet et al. 2010).

In order to increase flood protection in the flood plain, Skagit County and others are considering proposed modifications of current flood control operations (Steward and Associates, 2005; Skagit County, 2008).

Research Context

6

Are current or proposed alternative flood control operations adequate for managing the projected increases in flood risk in the Skagit River Basin?

Page 7: Alan  F.  Hamlet Se- Yeun  Lee

Reservoir Operations Modeling

Page 8: Alan  F.  Hamlet Se- Yeun  Lee

The Skagit River Simulation Model

Mount Vernon Concrete

Upper Baker

Lower Baker

Ross

Diablo Gorge

The Sauk and Cascade Rivers

The Baker River The Upper Skagit River

: Storage

: Run of River

Evaluate Current and Proposed Flood Control Operations Include Flood control, Hydropower, Instream Flow

Page 9: Alan  F.  Hamlet Se- Yeun  Lee

0

40,000

80,000

120,000

160,000

9 10 11 12 1 2 3 4 5 6 7 8

Stor

age

(cfs-

days

)

Month

Upper Baker

Current Flood Control CurveAlternative Flood Control Curve

Flood Control Curves

9

550,000

600,000

650,000

700,000

750,000

9 10 11 12 1 2 3 4 5 6 7 8

Stor

age (

cfs-d

ays)

Month

Ross

Current Flood Control CurveAlternative Flood Control Curve

60 kcfs-days

90 kcfs-days

37 kcfs-days

75 kcfs-days

Page 10: Alan  F.  Hamlet Se- Yeun  Lee

Simulated and Observed Daily Peak Flowsfor the Skagit River at Concrete

0

20,000

40,000

60,000

80,000

100,000

120,000

140,000

160,000

0 0.2 0.4 0.6 0.8 1

Dai

ly P

eak

Flow

(cfs

)

Probabilityof exceedance

USGS CurFC

Page 11: Alan  F.  Hamlet Se- Yeun  Lee

Effects of Climate Change

on Flood Risks

Page 12: Alan  F.  Hamlet Se- Yeun  Lee

Changes in Flood Risks under Natural Conditions

0

100,000

200,000

300,000

0 90 180 270 360

Peak

Flo

w (c

fs)

Peak Flow date (starting from October 1st)

His_unregulated

2040_unregulated

0

100,000

200,000

300,000

0 90 180 270 360

Peak

Flo

w (c

fs)

Peak Flow date (starting from October 1st)

His_unregulated2080_unregulated

Timing shifts of peak flows from spring to winter

Increases in magnitude of peak flows

2040s

2080s

ECHAM5 A1B Hybrid Delta Scenarios

Page 13: Alan  F.  Hamlet Se- Yeun  Lee

0

100,000

200,000

300,000

400,000

Unregulated CurFC AltFC

Q10

0 F

low

(cfs

)

2080s

100 year Flood

HistoricalHybrid delta _A1BAverage

Simulated 100-year Flood Statistics for the Skagit River near Mount Vernon

20 % 24 %Baseline Condition

Current flood control operations significantly reduce flood risk for future conditions in comparison with natural conditions

100-year flood risks are reduced only 3 % for the 2040s and 1 % for the 2080s under the alternative flood control curves.

+ 40%

0

100,000

200,000

300,000

400,000

Unregulated CurFC AltFC

Q10

0 F

low

(cfs

)

2040s

100 year Flood

HistoricalHybrid delta _A1BAverage

+ 23%

Page 14: Alan  F.  Hamlet Se- Yeun  Lee

Contribution of Ross and Upper Baker Inflows to

Mount Vernon Peak Flowsfor the Top 5 Flood Years

29,858 29,159 29,59332,162

56,98273,579

0

50,000

100,000

150,000

200,000

250,000

300,000

350,000

His 2040s 2080s

Peak

Flo

ws (

cfs)

1921/12/12

ROSS Upper Baker Other

17,85027,198

37,819

9,536

35,163

68,196

0

50,000

100,000

150,000

200,000

250,000

300,000

350,000

His 2040s 2080s

Peak

Flo

ws (

cfs)

1983/1/10

ROSS Upper Baker Other

8,860

13,47118,859

11,925

25,549

42,059

0

50,000

100,000

150,000

200,000

250,000

300,000

350,000

His 2040s 2080s

Peak

Flo

ws (

cfs)

2006/1/11

ROSS Upper Baker Other

18,96823,531

27,835

13,01222,006

38,327

0

50,000

100,000

150,000

200,000

250,000

300,000

350,000

His 2040s 2080s

Peak

Flo

ws (

cfs)

1986/11/24

ROSS Upper Baker Other

24,841 26,135 28,10434,290 32,478 40,156

0

50,000

100,000

150,000

200,000

250,000

300,000

350,000

His 2040s 2080s

Peak

Flo

ws (

cfs)

1995/11/29

ROSS Upper Baker Other

Page 15: Alan  F.  Hamlet Se- Yeun  Lee

Conclusions

• A warmer climate and wetter winters are projected to shift the seasonal timing of peak flows in the Skagit River from spring to fall/winter and increase the risk of flooding.

• Current and proposed alternative flood control storage in the headwaters helps mitigate the impacts of natural floods, but impounds a relatively small portion of the total flow in the lower Skagit River Basin.

• Increasing flood storage and/or moving evacuation timing earlier in the year have relatively little effect on regulated peak flows in our simulations.

Page 16: Alan  F.  Hamlet Se- Yeun  Lee

Conclusion (Cont’d)

• These results support the argument that climate change adaptation efforts in the Skagit will need to focus primarily on improved management of the floodplain to reduce vulnerability to increasing flood risk.

Page 17: Alan  F.  Hamlet Se- Yeun  Lee

Reference• Hamlet, A.F., Lee, S.Y., Mantua, N.J., Salathe, E.P., Snover, A.K., Steed, R.,

and Tohver, I., 2010. Seattle City Light climate change analysis for the city of Seattle, Seattle City Light Department, The Climate Impacts Group, Center for Science in the Earth System, Joint Institute or the Study of the Atmosphere and Ocean, University of Washington, Seattle, Washington. http://cses.washington.edu/db/pdf/snoveretalscl709.pdf.

• Skagit County, 2007. The Skagit River flood risk: Will you be prepared when disaster strikes? Flood Awareness Week, October 7-13, 2007, Washington.

• Steward and Associates, 2004. Environmental effects of additional flood control on the Baker river. Snohomish, Washington. http://www.skagitriverhistory.com/Skagit%20County%20Docs/Flood_Control_Impacts_Report_08%2011%2004.pdf

• Tohver, I.M., and Hamlet, A.F., 2010. Impacts of 21st century climate change on hydrologic extremes in the Pacific Northwest region of North America. The Columbia Basin Climate Change Scenarios Project (CBCCSP), chapter 7. http://www.hydro.washington.edu/2860/report/