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