1. Looking at Impacts of Climate Change on Seattle City Light Lynn Best, Director Environmental Affairs

2. Seattle City Light Municipal Electric Utility 395,000 customers About 90% of our power is hydro

4. Why Worry about Climate Change ? Started with a few staff in Power Planning and Power Operations UW Study on NW climate Impacts Nature of Our Business – Plan for the Long-Term – Assets Built for the Long-Term Seattle Public Utilities (water and drainage) and Water Utility Climate Alliance

5. Impacts of Climate on Our System Effect on hydrogenation Load Operations Fisheries Resources Infrastructure

8. Historical Observations Last 20 years – 11% lower April- September Ross Inflows 2 week earlier spring runoff since 1970 More frequent and larger floods on the Sauk River

9. PDO Positive PDO Negative No official PDO Classification

10. Note: Trends of runoffs shifting to earlier starts and ends Earlier Runoff Climate Change Historical Observations

11. Increased Sauk River Flood Magnitude Climate Change Impacts Detected

12. Increased Sauk River Flood Frequency Climate Change Historical Observations

13. Modeling Analysis Asked the Climate Impacts Group (CIG) for help Downscaling GCMs Site-specific Projections for the Skagit

14. Skagit Projections Provided by CIG 1.Snowpack and Monthly Stream flow at 9 Gages  Significant decline in snowpack (mean = 20%)  More flow in late-fall and winter  Lower summer flows 2.Extreme temperature and precipitation events  More warm wet days = greater flood potential 3.Weekly water temperature at selected river and stream sites  Substantial increases in summer water temperatures on Skagit River at Sedro Woolley and some eastside Ross Lake tributaries

15. Hydrologic Projections – Ross Basin Scenario EnsemblesEnsemble MeanHistorical Mean Snow water equivalent (A1B)Stream flow (A1B) Temperatures warm Earlier spring run-off Less snow accumulation &

16. Projected Number of Warm & Wet Days Warm, wet days increase significantly after mid 21 st century, driven primarily by warmer temperatures (some precipitation)

17. Extreme Flow Projections – Ross Reservoir Higher Flood Flows Lower Summer Low Flows

18. Stream Temperature Projections

19. Skagit at Sedro Woolley Skagit at NewhalemStetattle Creek Stream Temperature Projections Stream temperature projections indicate some sites on the Skagit River will exceed thermal thresholds for core summer salmon habitat (16°C –WA Department of Ecology) Sedro Woolley

20. One Simulated Projection of A1B Climate Change Scenario Ross Reservoir Level Operations Model Monthly Flow Data Reservoir refill by July 1 Flood Control Monthly instream flow requirements for fish Optimized generation

22. Downstream Impacts to Salmonids 20-, 50- and 100-year floods increase Increased chance of spill Substantial decline in 7-day low-flow level Scouring of salmon redds Reduced salmonid survival

23. Concerns Will storm frequency and severity increase causing more spill and impacts to salmon?

24. Concerns Will glacier recession increase bedload deposition near mouths of tributaries? How will this affect generation and fish access?

25. Concerns How will Project need to be operated to provide adequate instream flow during August and September to protect fish from thermal barriers or direct injury/mortality

27. Sea Level Rise

30. Future Work Adapt Operations in Response to: –Changing precipitation seasonal trends –Increased storms frequency and magnitude –Lower summer flows –New Federal Energy Regulatory Commission (FERC) license -- 2025 –Corps of Engineers flood control management Improve Modeling and Linkage of Climate Change Projections with Operational Tools –Explore use of Distributed Hydrology-Soil-Vegetation model (DHSVM) and dynamic downscaling techniques –Improve understanding of tributary and glacier contribution –Develop operations optimization model Operational constraints Scenarios and sensitivity analyses Daily time-step Protect Riverine Ecosystem, Endangered Species, and Anadromous Fish Assess Sea Level Rise Impacts