Looking at Impacts of Climate Change
on Seattle City Light
Lynn Best, DirectorEnvironmental Affairs
Seattle City Light
• Municipal Electric Utility
• 395,000 customers
• About 90% of our power is hydro
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
Impacts of Climate on Our System
• Effect on hydrogenation
• Load
• Operations
• Fisheries Resources
• Infrastructure
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
City of SeattleCity of Seattle
Ross Reservoir April-September Average Inflow
1500
2500
3500
4500
5500
6500
7500
1910 1930 1950 1970 1990 2010
Year
Flo
w (
cfs)
Note: Last 20 years mean is about 11% lower than the all years mean.
Significant declining trend
98-year average
PDO Positive
PDO Negative
No official PDO Classification
City of SeattleCity of Seattle
Ross Runoff Starting and Ending Dates
3/1
3/16
3/31
4/15
4/30
5/15
5/30
6/14
6/29
7/14
7/29
8/13
8/28
1971 1973 1975 1977 1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007 2009
Year
Da
te Start day
End day
Linear (Start day)
Linear (End day)
Note: Trends of runoffs shifting to earlier starts and ends
Earlier RunoffClimate Change Historical Observations
Increased Sauk River Flood MagnitudeClimate Change Impacts Detected
20,000
25,000
30,000
35,000
40,000
45,000
50,000
55,000
1930s 1940s 1950s 1960s 1970s 1980s 1990s 2000s
Decade
Flo
w (
cfs)
City of SeattleCity of Seattle
Increased Sauk River Flood FrequencyClimate Change Historical Observations
City of SeattleCity of Seattle
Modeling Analysis
• Asked the Climate Impacts Group (CIG) for help
• Downscaling GCMs
• Site-specific Projections for the Skagit
Skagit Projections Provided by CIG1. 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
City of SeattleCity of Seattle
Hydrologic Projections – Ross Basin
Scenario Ensembles Ensemble Mean Historical Mean
Snow water equivalent (A1B) Stream flow (A1B)
Temperatures warm Earlier spring run-offLess snow accumulation &
City of SeattleCity of Seattle
Projected Number of Warm & Wet Days
Warm, wet days increase significantly after mid 21st century, driven primarily by warmer temperatures (some precipitation)
City of SeattleCity of Seattle
Extreme Flow Projections – Ross Reservoir
City of SeattleCity of Seattle
18000
19000
20000
21000
22000
23000
20 50 100
Flood Return Interval (yrs)
Flo
w (
cfs)
historical
2040s
Higher Flood Flows
Lower Summer Low Flows
100
150
200
250
300
historical 2020s 2040s 2080s
Climate (A1B)
Flo
w (
cfs)
Stream Temperature Projections
Skagit at Sedro Woolley Skagit at Newhalem Stetattle 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
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
City of SeattleCity of Seattle
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
ConcernsWill storm frequency and severity increase causing more spill and impacts to salmon?
City of SeattleCity of Seattle
Concerns
Will glacier recession increase bedload deposition near mouths of tributaries?
How will this affect generation and fish access?
City of SeattleCity of Seattle
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
Sea Level Rise
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
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