Variational Assimilation (VAR) Presented by: Jerry Nunn Hydrologist In Charge West Gulf River...
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Transcript of Variational Assimilation (VAR) Presented by: Jerry Nunn Hydrologist In Charge West Gulf River...
![Page 1: Variational Assimilation (VAR) Presented by: Jerry Nunn Hydrologist In Charge West Gulf River Forecast Center October 28, 2003.](https://reader036.fdocuments.in/reader036/viewer/2022082711/56649f205503460f94c38597/html5/thumbnails/1.jpg)
Variational AssimilationVariational Assimilation(VAR)(VAR)
Presented by:
Jerry Nunn
Hydrologist In Charge
West Gulf River Forecast Center
October 28, 2003
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What is VAR?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.
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Purpose for VARPurpose 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.
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VARVAR
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.
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Schematic of VARSchematic of VAR
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VARVAR
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.
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WGRFC VAR ProjectWGRFC 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.
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Project LocationsProject Locations
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Basin CriteriaBasin 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
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WGRFC Project RequirementsWGRFC Project Requirements
Hourly stage data Hourly MAPX Climatological MAPE Calibrated 1 hour SAC-SMA parameters 1 hour unit hydrograph OFS segment definition
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Project StepsProject 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)
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AB_OPT SoftwareAB_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.
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Project AnalysisProject 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.
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VARPOST Forecast Group OutputVARPOST Forecast Group Output
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Future EnhancementsFuture 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.
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Possible Applications for VARPossible 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)
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Possible Applications for VAR Possible Applications for VAR (cont.)(cont.)
Flash Flooding– Site Specific– Unattended Models
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ContactsContacts Please contact the following people with any
questions relating to VAR:– OHD Team :
Dongjun Seo [email protected] Lee Cajina [email protected]
– WGRFC Team: Bob Corby [email protected] Tracy Howieson [email protected]