Lake Mendocino FORECAST INFORMED RESERVOIR OPERATIONS Final Viability Assessment December 2020 Lake Mendocino FIRO Steering Committee Jay Jasperse, Co-chair, Sonoma Water F. Martin Ralph, Co-chair, U.C. San Diego, Scripps Institution of Oceanography, Center for Western Weather and Water Extremes (CW3E) Michael Anderson, California Department of Water Resources Levi Brekke, U.S. Bureau of Reclamation Nicholas Malasavage, U.S. Army Corps of Engineers (USACE), San Francisco District Michael Dettinger, CW3E (formerly U.S. Geological Survey) Joseph Forbis, USACE, Sacramento District Joshua Fuller, National Oceanic and Atmospheric Administration (NOAA), National Marine Fisheries Service Cary Talbot, USACE, Engineer Research and Development Center Robert Webb, NOAA, Office of Atmospheric Research, Earth System Research Laboratory Alan Haynes, NOAA, National Weather Service, California-Nevada River Forecast Center Staff Support Arleen O’Donnell, Eastern Research Group, Inc. Robert Hartman, Robert K. Hartman Consulting Services Chris Delaney, Sonoma Water Ann DuBay, Sonoma Water John Mendoza, Sonoma Water David Ford, HDR, Inc. Mike Konieczki, HDR, Inc. Nathan Pingel, HDR, Inc. The final viability assessment (FVA) for Lake Mendocino was produced by the Lake Mendocino FIRO Steering Committee. The FVA does not address all USACE regulations and requirements for a potential update of the Water Control Manual at Coyote Valley Dam-Lake Mendocino. Because each watershed and location is unique, the analysis, results, and conclusions of the FVA are only applicable to Lake Mendocino. Contents Executive Summary ............................................................................................................ 1 Project Overview......................................................................................................... 1 Key Finding: FIRO is Currently Viable at Lake Mendocino and Will Deliver Significant Benefits ..................................................................................................................... 2 Key Finding: Further Investment in Research Will Increase Future Benefits at Lake Mendocino and Transferability to Other Locations .......................................................... 5 Key Finding: This Research and Operations Partnership Offers a Model for Successful Collaboration .............................................................................................................. 5 Recommendations ...................................................................................................... 6 Section 1. Introduction ....................................................................................................... 7 1.1 Overview .................................................................................................................. 7 1.2 The Russian River Watershed, Lake Mendocino, and Lake Sonoma ............................... 8 1.2.1 Russian River Watershed ..................................................................................... 8 1.2.2 Lake Mendocino ................................................................................................10 1.2.3 Lake Sonoma ....................................................................................................12 1.2.4 Russian River System Operation .........................................................................13 1.3 The Case for Change at Lake Mendocino ....................................................................13 1.4 FIRO and FIRO at Lake Mendocino ............................................................................16 1.5 Importance of Atmospheric River Research ................................................................17 1.6 Research and Operations ..........................................................................................18 1.7 Lake Mendocino Steering Committee .........................................................................22 Section 2. Evaluation of Existing Weather and Water Forecast Skill ........................................24 2.1 Existing Forecasting Methods ....................................................................................24 2.1.1 Weather Forecasting ..........................................................................................24 2.1.2 Water Forecasting .............................................................................................25 2.2 Forecast Verification .................................................................................................27 2.2.1 Deterministic Precipitation and Streamflow Forecasts ............................................27 2.2.2 Ensemble Forecasts ...........................................................................................29 2.3 Regional Variation in Forecast Skill ............................................................................33 2.4 Sustainability of Existing and Future Forecast Services ................................................35 Section 3. Evaluation of FIRO WCP Alternatives Using Existing Streamflow Forecasts ..............36 3.1 Background .............................................................................................................36 3.2 WCP Alternatives .....................................................................................................36 3.2.1 Baseline WCP ....................................................................................................38 3.2.2 EFO ..................................................................................................................38 i 3.2.3 Hybrid EFO .......................................................................................................41 3.2.4 Modified Hybrid EFO ..........................................................................................41 3.2.5 Five-Day Deterministic Forecast ..........................................................................42 3.3 WCP Performance Metrics .........................................................................................43 3.4 Procedure ...............................................................................................................43 3.4.1 Study Boundary Conditions .................................................................................43 3.4.2 Analysis Methods ...............................................................................................44 3.5 Results ....................................................................................................................46 3.5.1. Key Findings ....................................................................................................46 3.5.2 Making Sense of the Metrics ...............................................................................58 3.6 Additional Robustness Testing ...................................................................................59 3.7 Summary ................................................................................................................59 Section 4. Interim Operations .............................................................................................61 4.1 Description and Analysis of Planned Major Deviations .................................................61 4.1.1 WY 2019 Major Deviation ...................................................................................61 4.1.2 WY 2020 Major Deviation ...................................................................................64 4.2 Decision Support System and Situational Awareness ...................................................66 4.2.1 Interactive FIRO on California Data Exchange Center ...........................................66 4.2.2 CW3E Website ..................................................................................................69 4.2.3 Major Deviation Operations ................................................................................70 4.2.4 Virtual Operations ..............................................................................................71 4.3 Summary ................................................................................................................73 Section 5. FIRO Gains Through Research, Studies, and Enhanced Observations .....................74 5.1 Introduction ............................................................................................................74 5.1.1 Scientific Advancements that Contribute to FIRO’s Viability at Lake Mendocino .......74 5.1.2 Potential Gains Through Additional Research and Development .............................76 5.1.3 Research and Operations: A Blueprint for Success ................................................76 5.2 Weather Forecast Improvements ...............................................................................77 5.2.1 Current Forecast Procedures ...............................................................................78 5.2.2 Research to Improve Week One Forecast Skill .....................................................79 5.2.3 Machine Learning and Bias Correction .................................................................84 5.2.4 Decision Support ...............................................................................................84 5.2.5 Opportunities for Future Gains ............................................................................86 5.3 Enhanced Observations ............................................................................................87