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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 ?.

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Looking at impacts of climate change on seattle city light lynn best director environmental affairs

Looking at Impacts of Climate Change onSeattle City LightLynn Best, DirectorEnvironmental Affairs

Seattle city light
Seattle City Light

  • Municipal Electric Utility

  • 395,000 customers

  • About 90% of our power is hydro

Why worry about climate change
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
Impacts of Climate on Our System

  • Effect on hydrogenation

  • Load

  • Operations

  • Fisheries Resources

  • Infrastructure

Historical observations

City of Seattle

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

PDO Positive

PDO Negative

No official PDO Classification

City of Seattle

Climate Change Historical Observations

Earlier Runoff

Note: Trends of runoffs shifting to earlier starts and ends

City of Seattle

Climate Change Impacts Detected

Increased Sauk River Flood Magnitude

City of Seattle

Climate Change Historical Observations

Increased Sauk River Flood Frequency

Modeling analysis
Modeling Analysis

  • Asked the Climate Impacts Group (CIG) for help

  • Downscaling GCMs

  • Site-specific Projections for the Skagit

City of Seattle

Skagit Projections Provided by CIG

  • Snowpack and Monthly Stream flow at 9 Gages

    • Significant decline in snowpack (mean = 20%)

    • More flow in late-fall and winter

    • Lower summer flows

  • Extreme temperature and precipitation events

    • More warm wet days = greater flood potential

  • 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

Hydrologic projections ross basin

City of Seattle

Hydrologic Projections – Ross Basin

Snow water equivalent (A1B)

Stream flow (A1B)

Temperatures warm

Less snow accumulation


Earlier spring run-off

Scenario Ensembles

Ensemble Mean

Historical Mean

Projected number of warm wet days

City of Seattle

Projected Number of Warm & Wet Days

Warm, wet days increase significantly after mid 21st century, driven primarily by warmer temperatures (some precipitation)

Extreme flow projections ross reservoir

Higher Flood Flows

City of Seattle

Extreme Flow Projections – Ross Reservoir

Lower Summer Low Flows

Stream temperature projections1
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

City of Seattle

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

Downstream impacts to salmonids
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

City of Seattle


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


City of Seattle


Will glacier recession increase bedload deposition near mouths of tributaries?

How will this affect generation and fish access?


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

Future work
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