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March 21, 2011

Current CBRFC Water Supply Forecast Methodology. March 21, 2011. Kevin Werner NWS Colorado Basin River Forecast Center. Colorado Basin River Forecast Center. One of 13 River Forecast Centers Established in the 1940s for water supply forecasting Three primary missions:

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March 21, 2011

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  1. Current CBRFC Water Supply Forecast Methodology March 21, 2011 Kevin Werner NWS Colorado Basin River Forecast Center

  2. Colorado Basin River Forecast Center One of 13 River Forecast Centers Established in the 1940s for water supply forecasting Three primary missions: 1. Seasonal Water supply forecasts for water management 2. Daily forecasts for flood, recreation, water management 3. Flash flood warning support www.cbrfc.noaa.gov

  3. Water Supply Forecasts • Generated seasonally • Typically January through June • Updated monthly or as needed • Forecast runoff volume (usually April – July) • Probabilistic

  4. Web Reference: www.cbrfc.noaa.gov/gmap/gmapm.php?wcon=checked

  5. Water Supply Forecast Methods Statistical Forecasting Statistical Regression Equations Primary NOAA/RFC forecast method from 1940’s to mid 1990’s. Primary NRCS/NWCC forecast method Historical Relationships between flow, snow, & precipitation (1971-2000+) Tied to a fixed runoff period (inflexible) Ensemble Simulation Model Forecasting A component of a continuous conceptual model (NWSRFS) Continuous real time inputs (temperature, precipitation, forecasts) Accounts for soil moisture states (SAC-SMA) - drives runoff efficiency Builds and melts snowpack (Snow-17) – output feeds SAC-SMA Flexible run date, forecast period, forecast parameters. Evolving toward ESP as primary forecast tool at NOAA/RFCs

  6. ? Statistical Water Supply (SWS) • Equations built on relationships between the inputs and the output Output Variable: April-July streamflow volume at Provo-Woodland

  7. Source: NRCS Statistical Water Supply (SWS) • Equations built on relationships between the inputs and the output Input Variable: Trial Lake Snow

  8. Water Supply Forecast Methods Statistical Forecasting Statistical Regression Equations Primary NOAA/RFC forecast method from 1940’s to mid 1990’s. Primary NRCS/NWCC forecast method Historical Relationships between flow, snow, & precipitation (1971-2000+) Tied to a fixed runoff period (inflexible) Ensemble Simulation Model Forecasting A component of a continuous conceptual model (NWSRFS) Continuous real time inputs (temperature, precipitation, forecasts) Accounts for soil moisture states (SAC-SMA) - drives runoff efficiency Builds and melts snowpack (Snow-17) – output feeds SAC-SMA Flexible run date, forecast period, forecast parameters. Evolving toward ESP as primary forecast tool at NOAA/RFCs

  9. Forecast precip / temp General RFC Model Hydrologic Model Analysis hydrologic expertise & judgment model guidance River Forecast System Weather and Climate Forecasts River Forecasts Outputs Graphics Analysis & Quality Control parameters Observed Data Calibration

  10. RFC Models • RFC forecast uses a snow model and a rainfall-runoff model: • SNOW-17: Temperature index model for simulating snowpack accumulation and melt • Sacramento Soil Moisture Accounting Model: Conceptual hydrologic model used to generate runoff Snow Model: SNOW-17 Temperature Index Snow model

  11. Calibration • Process to assign parameter values to the runoff and snow modules within the model. Unique set for each basin (and sub-basin) • Quality of calibration can vary greatly from basin to basin depending on data availability, period or record, quality of data, hydrology of the basin, etc.

  12. San Juan Basin

  13. San Juan-Pagosa Springs(PSPC2)

  14. San Juan-Pagosa Springs(PSPC2) Upper (11000-12644) Middle (8500-11000) Lower (7198-8500)

  15. Weather and Climate Forecasts • RFC forecast system incorporates both weather and climate forecasts: • Weather forecasts integrated into daily operations with forecaster control over point and basin average values • Water supply forecasts typically only use QPF during late season or in lower basin • When QPF is used, it is used in a deterministic manner • Climate forecasts integrated into seasonal water supply forecasts through probability shifts of forcing ensemble • Climate forecasts are typically only considered in lower basin and only in ENSO years

  16. Forecast precip / temp Forecast Process Hydrologic Model Analysis hydrologic expertise & judgment model guidance River Forecast System Weather and Climate Forecasts River Forecasts Outputs Graphics Rules, values, other factors, politics Analysis & Quality Control parameters Observed Data Calibration Decisions

  17. CBRFC Research Needs 3. Develop reliable ensemble forecast system 4. Improve physical process understanding and modeling 2. Improve use of weather and climate forecasts 1. Improve precipitation analysis 5. Decision Support: Work with stakeholders to use forecasts

  18. Water Supply Forecast Overview SWS (Statistical Prediction) Official Coordinated Forecast ESP (Hydrologic Model Prediction) (River Forecast Centers) VIPER (Statistical Prediction) Forecast Coordination (Water and Climate Center) Other Inputs . . . . Decisions Water Managers and Users

  19. Statistical 50% exceedance Forecast: 222 kac-ft

  20. Ensemble 50% exceedance Forecast: 230 kac-ft

  21. ESP applications • CBRFC currently provides “raw” ensemble time series forecasts to several groups: • Denver Water • Pacificorps (Bear River) • USBR (Gunnison, Utah, and MTOM) • Forecasts updated daily in winter/spring • Available via CBRFC webpage

  22. Applications of Probabilistic Flow Forecasts • Denver Water: • Long history of using ensemble forecasts for risk management • Download CBRFC ensemble forecasts into reservoir operations spreadsheet (right) • Optimize reservoir operations by minimizing negative impacts • Southern CA MWD: • Requested forecast for probability of equalization releases from Lake Powell • USBR determines inflow volume required to trigger equalization from 24 month study • CBRFC uses regulated ESP forecast to determine probability of reaching the required volume

  23. Forecast Coordination • Forecasts are coordinated with NRCS on a monthly basis. Forecasters at each agency compare forecasts, analyze differences, and come up with a official, coordinated forecast. NRCS Preferred Forecast: 235 kac-ft NOAA Preferred Forecast: 225 kac-ft Coordinated Forecast: 230 kac-ft

  24. Water Supply Forecast Overview SWS (Statistical Prediction): 222 KAF Official Coordinated Forecast: 230 KAF ESP (Hydrologic Model Prediction) : 230 KAF (River Forecast Centers) VIPER (Statistical Prediction) : 236 KAF Forecast Coordination NOAA: 225 KAF NRCS: 236 KAF (Water and Climate Center) Other Inputs . . . . Decisions Water Managers and Users

  25. Forecast Verification Beginning in 2008, CBRFC began verifying all water supply forecasts both for current year and systematically over previous years Current forecast system has skill SWS and ESP have somewhat different error characteristics Skill is typically near zero in Jan/Feb and increases substantially into spring www.cbrfc.noaa.gov -> Water Supply -> Verification

  26. Discussion • Unmet stakeholder requirements: • Assessment and incorporation of weather and climate forecasts into water supply forecasts • Forecast horizon out to two years • Objective (and therefore repeatable) forecast system • CBRFC is committed to working with partners (you all) to meet these and other requirements • Need to move forward in a responsible way that builds on or bridges from current forecast system

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