Evapotranspiration Workshop

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Calibration for Historical Crop ET Estimates – A Process. Evapotranspiration Workshop. Ivan A. Walter, P.E. Ivan’s Engineering, Inc. Kc ETstzd vs SCS BC. Kc ET stzd is more accurate than SCS BC Kc -- Generate from measurement at known sites Kc -- Transferrable - PowerPoint PPT Presentation

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Calibration for Historical Crop ET Estimates A ProcessIvan A. Walter, P.E.Ivans Engineering, Inc.Evapotranspiration Workshop3/12/20101Ivan A. Walter, P.E.1Kc ETstzd vs SCS BCKc ETstzd is more accurate than SCS BCKc -- Generate from measurement at known sitesKc -- TransferrableETstzd ET professional & researchers have acceptedSCS BC Crop Coefficients derived where???SCS BC Requires local calibration3/12/20102Ivan A. Walter, P.E.Why Isnt Kc ETstzd UsedAnswers to Why not?SCS BC is well accepted in Colo. Water Court. Do not have the data for ETstzd Do not have the Kcs

3/12/20103Ivan A. Walter, P.E.What is Desirable ResultJust some number for ETcAccurate daily Temp, Rs, U, & RhAccurate daily ETrs & ETosAccurate monthly ETrs & ETosExcel files & Programs for analysis

3/12/20104Ivan A. Walter, P.E.Criteria (ASCE Task Committee)UnderstandableDefensibleSimplification without loss of accuracyBased on & Traceable to Experimental Data3/12/20105Ivan A. Walter, P.E. 3/12/2010Ivan A. Walter, P.E.63/12/2010Ivan A. Walter, P.E.73/12/2010Ivan A. Walter, P.E.8Raw Data >>>>>> ETcDownload data from Web siteQC the data Select good dataCalc ETrs, ETos, and ETHrgvCalibration Calcs with good dataCOEFHgrv x ETHrgv = ETrs COEF1Hgrv x ETHrgv = ETos

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Begin HereStandardized Reference ET Equation:3/12/201010Ivan A. Walter, P.E.Begin Here w/ Data from Web3/12/201011Ivan A. Walter, P.E.

Calculate & Analyze & CompareStandardized Reference ET Equation:3/12/201012Ivan A. Walter, P.E.

1985 Hargreaves Equation:Final ProductStandardized Reference ET valuesShort Crop: ETosTall Crop: ETrsDaily values3/12/201013Ivan A. Walter, P.E.13Step 1: XXX COAG.xlsDownload data from COAGMet siteQC the dataIdentify the Good DataFix small gaps & errorsThrow out everything else3/12/201014Ivan A. Walter, P.E.Step 2: ColCrbt2.exe -- ApplicationInput data from XXX COAG.xlsText file XXXEtrData.prnCalculates Reference ET (daily)ETrsASCE PM Etr, 1982 Kimberly Penman ETrETosASCE PM ETo, Hargreaves ETo

3/12/201015Ivan A. Walter, P.E.Step 3: Colcrbt2.exe -- ResultsLinear Regression Analysis (daily)Zero interceptMonthly Ratio: ETrs to ETHgrvMonthly Ratio: ETos to ETHgrvMonthly Ratio: ETrs to ETos Regression Coef & SEE

3/12/201016Ivan A. Walter, P.E.Step 3 Results: Ratio ETrs : ETHrgv3/12/2010Ivan A. Walter, P.E.17MAYJUNJULAUGSEPFort Morgan(Tdpt Adjusted) 1995 - 20061.401.361.271.251.37Fort Collins 03 1999 - 20061.481.411.381.381.56Center 1996 - 20061.541.381.151.181.47Avondale 1994 - 20081.301.331.221.161.22Rocky Ford 1994 -20081.321.361.221.171.17Yuma 1996 - 20061.581.541.341.281.47Fruita 1999 20061.341. Jacket 1992 - 20081.311. @ Center: Ratio ETrs : ETHrgv3/12/2010Ivan A. Walter, P.E.18MAYJUNJULAUGSEPAll1.541.381.151.181.4719961.681. 3 Results: Ratio ETos : ETHrgv3/12/2010Ivan A. Walter, P.E.19MAYJUNJULAUGSEPFort Morgan(Tdpt Adjusted) 1995 - 20061.021.010.960.961.00Fort Collins 03 1999 - 20061. 1996 - 20061.151.060.930.941.09Avondale 1994 - 20081.031.010.940.930.99Rocky Ford 1994 -20081.041.040.940.940.95Yuma 1996 - 20061. 1999 20061.000.970.900.880.91Yellow Jacket 1992 - 20081.011.010.980.991.05Step 4: ETRETOH 2.exeCalculate ETrs & ETos using ETHgrvInput FileDataT&P.prn from XXX COAG.xlsLatitude, Tmax, Tmin, TavgCOEFHRGV.datMonthly Coefficient all Station (15 max.)3/12/201020Ivan A. Walter, P.E.Step 4: COEFHGRV.dat3/12/201021Ivan A. Walter, P.E.

Step 4: ETRETOH 2.exeCalculation of ETrs & ETos using 1985 HargreavesETrs = COEF x ETHgrv (Daily)ETos = COEF1 x ETHgrv (Daily)

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Step 4: Final ResultsYear, DOY, Month, Day, ETrs,ETos, Precip. 3/12/201023Ivan A. Walter, P.E.

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Process -- Historical ETref EstimatesCoAgMet DataXXX COAG.xls -- QC for Good dataColcrbt2.exe -- Calc Monthly Hgrv FactorsETRETOH 2.exe - Calculate ETrs & ETos 3/12/201032Ivan A. Walter, P.E.Meadow Grass ETReview of MethodsRecommendation for Calculation ETc3/12/2010Ivan A. Walter, P.E.33Reported ProceduresSCS BC Pasture Grass10% / 1,000 m. change in elevationASCE Manual 70 does not recommendPochop Method -- ASAE 1984Limited to Alfalfa (9%) & Turf (6%)Adjusted kt --- thus not true SCS BCAdjust from elevation Coefficient derivedWyoming3/12/201034Ivan A. Walter, P.E.Reported ProceduresDenver Water Board, BC k coef.South Park, Elev. 8,900 ft mslStandard BC not modified BCLocal calibrationET calculated as:Lysimeter water use + Precipitation (100%)ETirr wtr = ETc - Precipitation3/12/201035Ivan A. Walter, P.E.Recommend Transferrable Kc Smiths Gunnison basin Hargreaves Monthly CoefficientsLetter Describing included in MaterialsMaly & Walter Kcs Meadow GrassMemo Describing process included in Materials3/12/201036Ivan A. Walter, P.E.Hargreaves Kcs for Meadow GrassMultiple Sites -- 5 years of dataMay=1.16June=1.28July=1.04August=0.86September =0.883/12/201037Ivan A. Walter, P.E.3/12/2010Ivan A. Walter, P.E.38

Meadow Grass Kc -- Derived using Calibrated HargreavesSoftware & Documents ProvidedXXX COAG.xls -- QC dataColcrbt2.exe -- Calc Monthly Coef.ETRETOH 2.exe -- Calc ETrs & ETos Example Input and Output filesMemo: Coefficients for Meadow GrassSmith Letter: Hargreaves Kc M.GrassDaily Ra calculation Application3/12/201039Ivan A. Walter, P.E.3/12/2010Ivan A. Walter, P.E.40