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