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Variational Assimilation (VAR) for Improved Hydrological Forecasting

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eldon
18 diapositives · 367 Views · Oct 21, 2014

The Variational Assimilation (VAR) software, developed by Jerry Nunn from the West Gulf River Forecast Center, efficiently estimates soil moisture content for the SAC-SMA model using variational techniques prevalent in meteorology. VAR adjusts SAC-SMA state variables based on observed streamflow and climate data, enabling more accurate forecasting. Originally created in 2002, VAR has expanded to include diverse basins across Texas and outputs time series data that integrates back into operational forecasting systems. Future enhancements may incorporate broader applications in flash flooding and distributed modeling.

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Variational Assimilation (VAR) for Improved Hydrological Forecasting
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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