Impacts of Climate Change on the Tualatin River Basin Nathan VanRheenen, Erin Clancy, Richard Palmer, PhD, PE Dept. of Civil and Environmental Engineering University of Washington

Talk Overview Background Research Approach Impacts on Meteorology Impacts on Hydrology Impacts on System Yield Final Conclusions

Insight from a Notable American Philosopher The future ain't what it used to be. -Yogi Berra

It's time for those of us who work on climate change to help the public and policymakers understand the evidence: Climate change is real, well underway, and poses severe risks to the United States and the world. Dr. Peter Gleick Director, The Pacific Institute 2003 MacArthur Fellowship Award Winner

Translating the Challenge to Regional Analysis What are the likely impacts of climate change on regional watersheds? Types of impacts Magnitude of impacts Mitigation responses Case Studies Seattle Water Department Portland Water Bureau Tualatin Basin

Setting Rain-driven watershed (no snow impacts) Multiple uses: M&I, Ag, Fish, Recreation 500,000 customers (M&I) Agriculturally productive Water Quality Concerns (temperature) Current system is fully allocated M&I demands expected to increase 400% by 2050 Ag demands, 50% by 2050 System highly sensitive to changes in summer flows System expansion is under consideration

Models for Evaluating Climate Change General Circulation Models  Tualatin River Integrated Management System (TRIMS) Hydrology Model, EPA BASINS  Tualatin River Integrated Management System (TRIMS)

Impacts on Meteorology

Global climate models operate at a scale of 2-5° latitude Global data must be downscaled to the local station scale in order to assess the impacts of climate change on water resources.

Historical Meteorology Hydrology Model Climate Signals Predicted Meteorology From Climate Signals to Runoff Predicted Runoff

Temperature Signals from GCMs

Precipitation Signals from GCMs

Impacts on Hydrology

EPA BASINS Watershed and subwatershed delineation: ArcGIS add-on Rainfall-runoff simulation: HSPF (Stanford Watershed Model) Can be extended to model water quality Calibrated to match monthly flows at six stations Hydrology Model

BASINS Model Nodes

Impacts on Hydrology: Hagg Lake Inflows

Impacts on Hydrology: Summer Flows

Impacts on Water Resources System

Tualatin River Integrated Management System (TRIMS)

TRIMS Description Dynamic model of the basin Purpose: Calculate system yield Incorporates Major system features and operations BASINS inflows M&I and Ag water supply demands Present, Contracted, 2050 CWS environmental targets (Present, 2050) Instream flow targets Scoggins Dam expansion alternatives Increase dam elevation by 20 ft, 40 ft

TRIMS Schematic

Hagg Lake Storage – Current System

Hagg Lake Storage – 40 ft Expansion

Hagg Lake Yield – Current System acre-ft/100 days = 130mgd acre-ft/150 days = 87 mgd

Hagg Lake Yield – Current System

Hagg Lake Yield – 20 ft Expansion

Hagg Lake Yield – 40 ft Expansion

Hagg Lake “Expansion Schedule”

Conclusion

Impacts on Temperature and Precipitation Increase in temperature of 2-4 °F Wetter winters, drier summers Impacts on Streamflow 10-20% lower flows in summer, wetter winters Impacts on Yield Decreases 1.5% per decade for current system and current demands

Conclusion System Expansion without climate change 97% reliable yield increased from 38,000 acre-ft per year to 60,000 acre-ft (20-ft expansion) and 73,000 acre-ft (40-ft expansion) System Expansion with climate change by 2040 Yield shifts downward by about 4,000 acre-ft Climate change impacts suggest expansion needed 5-8 years earlier