Transcript Lynn Best
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