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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. 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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Alan F. Hamlet Se- Yeun Lee

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  1. 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 (SC2) Climate Impacts Group, UW

  2. 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.

  3. Floodplain Development in the Skagit

  4. 21st Century Climate Impacts for the Pacific Northwest Region Mote, P.W. and E. P. Salathe Jr., 2010: Future climate in the Pacific Northwest, Climatic Change, DOI: 10.1007/s10584-010-9848-z

  5. 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

  6. Research Context • 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). Are current or proposed alternative flood control operations adequate for managing the projected increases in flood risk in the Skagit River Basin?

  7. Reservoir Operations Modeling

  8. The Skagit River Simulation Model Ross Upper Baker Diablo Gorge Lower Baker The Baker River The Upper Skagit River Concrete Mount Vernon The Sauk and Cascade Rivers : Storage • Evaluate Current and Proposed Flood Control Operations • Include Flood control, Hydropower, Instream Flow : Run of River

  9. Flood Control Curves 60kcfs-days 90kcfs-days 37kcfs-days 75kcfs-days

  10. Simulated and Observed Daily Peak Flowsfor the Skagit River at Concrete

  11. Effects of Climate Change on Flood Risks

  12. Changes in Flood Risks under Natural Conditions 2040s • Timing shifts of peak flows from spring to winter • Increases in magnitude of peak flows 2080s ECHAM5 A1B Hybrid Delta Scenarios

  13. Simulated 100-year Flood Statistics for the Skagit River near Mount Vernon + 23% + 40% Baseline Condition 20 % 24 % • 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.

  14. Contribution of Ross and Upper Baker Inflows to Mount Vernon Peak Flowsfor the Top 5 Flood Years

  15. 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.

  16. 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.

  17. 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/

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