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Variational Assimilation (VAR)

Variational Assimilation (VAR). Presented by: Jerry Nunn Hydrologist In Charge West Gulf River Forecast Center October 28, 2003. What is VAR?. Software that produces initial estimates of soil moisture content for SAC-SMA.

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Variational Assimilation (VAR)

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  1. Variational Assimilation(VAR) Presented by: Jerry Nunn Hydrologist In Charge West Gulf River Forecast Center October 28, 2003

  2. What is VAR? • Software that produces initial estimates of soil moisture content for SAC-SMA. • Based on variational assimilation popularized by widespread use in meteorology and oceanography. • Solves large-scale inverse problems in dynamic systems via least squares minimization.

  3. Purpose for VAR • Given the latest streamflow observation, MAPX and MAPE estimates, and the initial SAC-SMA state variables: • VAR adjusts the SAC-SMA state variables and the MAPX and MAPE estimates such that the resulting model simulation matches the observed. • Allows the forecaster to start with more accurate SAC – SMA states for forecast runs. • Possible replacement of the current OFS operation; SS-SAC.

  4. VAR • VAR is currently a stand-alone program that runs independent of OFS, however, it uses data stored within OFS. • VAR ingests time series data from OFS in a text format. • VAR also utilizes special decks that include the SAC-SMA parameters and unit hydrograph definitions. • After VAR completes, it outputs time series data that can be ingested back into OFS.

  5. Schematic of VAR

  6. VAR • The software was originally developed on the AWIPS – HP-UX system. • July, 2003 - Software also made available in Linux format. • WGRFC currently utilizing the Linux version to capitalize on the faster processing speed.

  7. WGRFC VAR Project • Implemented in 2002 • Original project consisted of 6 headwater basins located in eastern Texas • Expanded project in 2003 • Added 10 basins throughout Texas • This was done to account for the varied hydrologic conditions throughout the WGRFC area.

  8. Project Locations

  9. Basin Criteria • Basins selected for the VAR project had to meet the following criteria: • Headwater basin • Basin defined in operational model • Hourly stage data available • Candidate basins also needed to vary in the following areas: • Basin Size (50 – 700 square miles) • Time to peak in the unit hydrograph (4 –80 hours) • Diverse basin shape and geomorphology

  10. WGRFC Project Requirements • Hourly stage data • Hourly MAPX • Climatological MAPE • Calibrated 1 hour SAC-SMA parameters • 1 hour unit hydrograph • OFS segment definition

  11. Project Steps • Preparation of historical data sets for observed stage and mean areal precipitation. (WGRFC) • Development of climatological MAPE using Calibration Assistance Program (CAP). (OHD) • Development of 1 hour unit hydrograph. (OHD) • Refinement of SAC-SMA parameters for use in a 1 hour model. (OHD) • Creation of all required OFS components. (WGRFC)

  12. AB_OPT Software • Created by OHD for assistance in the implementation of VAR. • Available in both a HP-UX and Linux version. • Ingests historical stage and MAPX data. • Software estimates long term biases in MAPX and MAPE climatology based upon the historical data. • Uses these biases to develop a 1 hour empirical unit hydrograph and refined SAC-SMA parameters.

  13. Project Analysis • Project Output • 1 hour VAR adjusted time-series (VAR) • 1 hour SAC-SMA time-series (OFS) • Without modification • With forecaster modification • 6 hour operational SAC-SMA time-series (OFS) • All time-series mentioned above are produced and archived hourly for analysis purposes.

  14. VARPOST Forecast Group Output

  15. Future Enhancements • Expansion to non-headwater locations • Routed flow locations • Reservoirs • Inclusion of unit hydrograph theory in the VAR process • Currently VAR will only make modifications based on rainfall, evaporation and sac-sma parameters.

  16. Possible Applications for VAR • Enhancement to RFC Models • Provides a way to maintain the SAC-SMA contents. • Better initialization of SAC-SMA contents will allow for improved forecasts. • Distributed Modeling • Development of new software for use by field offices • (i.e. AB_OPT)

  17. Possible Applications for VAR (cont.) • Flash Flooding • Site Specific • Unattended Models

  18. Contacts • Please contact the following people with any questions relating to VAR: • OHD Team : • Dongjun Seo Dongjun.Seo@noaa.gov • Lee Cajina Lee.Cajina@noaa.gov • WGRFC Team: • Bob Corby Robert.Corby@noaa.gov • Tracy Howieson Tracy.Howieson@noaa.gov

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