Ivan A. Walter, P.E. 1
Calibration for Historical Crop ET Estimates – A Process
Ivan A. Walter, P.E.
Ivan’s Engineering, Inc.
EVAPOTRANSPIRATION WORKSHOP
3/12/2010
Ivan A. Walter, P.E. 2
Kc ETstzd vs SCS BCKc ETstzd vs SCS BC
Kc ETstzd is more accurate than SCS BC– Kc -- Generate from measurement at known sites– Kc -- Transferrable– ETstzd – ET professional & researchers have
accepted– SCS BC – Crop Coefficients derived where???– SCS BC – Requires local calibration
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Why Isn’t Kc ETstzd UsedWhy Isn’t Kc ETstzd Used Answers to “Why not?”
– SCS BC is well accepted in Colo. Water Court.
– Do not have the data for ETstzd – Do not have the Kc’s
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What is Desirable ResultWhat is Desirable Result Just some number for ETc Accurate daily Temp, Rs, U, & Rh Accurate daily ETrs & ETos
Accurate monthly ETrs & ETos
Excel files & Programs for analysis
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Criteria (ASCE Task Committee)Criteria (ASCE Task Committee)
Understandable Defensible Simplification without loss of accuracy Based on & Traceable to Experimental
Data
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Apr May Jun Jul Aug Sep0
2
4
6
8
10
12
Rocky Ford ETrs
ETrs ETrs Est
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May Jun Jul Aug Sep80%
85%
90%
95%
100%
105%
110%
Rocky Ford: Est as % of Actual
ETrs Est /: ETrs ETos Est / ETos
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1-Apr 1-May 1-Jun 1-Jul 1-Aug 1-Sep 1-Oct0
0.1
0.2
0.3
0.4
0.5
0.6
Fort Morgan -- 2005 Daily Data
ETrs
ETrs Est
inch
es
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Raw Data >>>>>> ETcRaw Data >>>>>> ETc
Download data from Web site QC the data – Select good data Calc ETrs, ETos, and ETHrgv
Calibration Calc’s with good data COEFHgrv x ETHrgv = ETrs COEF1Hgrv x ETHrgv = ETos
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)1(
)(273
)(408.0
2
2
uC
eeuT
CGR
ETd
asn
n
ref
Begin Here
Standardized Reference ET Equation:
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Begin Here w/ Data from Web
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)1(
)(273
)(408.0
2
2
uC
eeuT
CGR
ETd
asn
n
ref
Calculate & Analyze & Compare
Standardized Reference ET Equation:
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ameano RTTTET )8.17()(0023.0 5.0minmax
1985 Hargreaves Equation:
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Final ProductFinal Product
Standardized Reference ET values– Short Crop: ETos– Tall Crop: ETrs– Daily values
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Step 1: XXX COAG.xlsStep 1: XXX COAG.xls
Download data from COAGMet site QC the data
– Identify the Good Data– Fix small gaps & errors– Throw out everything else
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Step 2: ColCrbt2.exe -- ApplicationStep 2: ColCrbt2.exe -- Application
Input data from XXX COAG.xls– Text file XXXEtrData.prn
Calculates Reference ET (daily)– ETrs– ASCE PM Etr, 1982 Kimberly Penman ETr– ETos– ASCE PM ETo, Hargreaves ETo
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Step 3: Colcrbt2.exe -- ResultsStep 3: Colcrbt2.exe -- Results
Linear Regression Analysis (daily) Zero intercept Monthly Ratio: ETrs to ETHgrv
Monthly Ratio: ETos to ETHgrv
Monthly Ratio: ETrs to ETos Regression Coef & SEE
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Step 3 Results: Ratio ETrs : ETHrgvStep 3 Results: Ratio ETrs : ETHrgv
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MAY JUN JUL AUG SEPFort Morgan(Tdpt Adjusted) 1995 - 2006 1.40 1.36 1.27 1.25 1.37Fort Collins 03 1999 - 2006 1.48 1.41 1.38 1.38 1.56Center 1996 - 2006 1.54 1.38 1.15 1.18 1.47Avondale 1994 - 2008 1.30 1.33 1.22 1.16 1.22Rocky Ford 1994 -2008 1.32 1.36 1.22 1.17 1.17Yuma 1996 - 2006 1.58 1.54 1.34 1.28 1.47Fruita 1999 2006 1.34 1.28 1.15 1.13 1.21Yellow Jacket 1992 - 2008 1.31 1.29 1.22 1.24 1.36
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Results @ Center: Ratio ETrs : ETHrgvResults @ Center: Ratio ETrs : ETHrgv
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MAY JUN JUL AUG SEPAll 1.54 1.38 1.15 1.18 1.47
1996 1.68 1.25 1.06 1.14 1.471997 1.31 1.32 1.16 1.06 1.251998 1.62 1.56 1.08 1.15 1.481999 1.56 1.43 1.09 1.12 1.382000 1.43 1.30 1.11 1.17 1.572001 1.45 1.35 1.07 1.15 1.522002 1.56 1.36 1.15 1.23 1.342003 1.50 1.38 1.21 1.17 1.482004 1.61 1.38 1.23 1.37 1.562005 1.54 1.44 1.24 1.26 1.572006 1.57 1.43 1.17 1.15 1.47
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Step 3 Results: Ratio ETos : ETHrgvStep 3 Results: Ratio ETos : ETHrgv
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MAY JUN JUL AUG SEPFort Morgan(Tdpt Adjusted) 1995 - 2006 1.02 1.01 0.96 0.96 1.00Fort Collins 03 1999 - 2006 1.07 1.03 1.03 1.03 1.10Center 1996 - 2006 1.15 1.06 0.93 0.94 1.09Avondale 1994 - 2008 1.03 1.01 0.94 0.93 0.99Rocky Ford 1994 -2008 1.04 1.04 0.94 0.94 0.95Yuma 1996 - 2006 1.14 1.13 1.03 0.99 1.07Fruita 1999 2006 1.00 0.97 0.90 0.88 0.91Yellow Jacket 1992 - 2008 1.01 1.01 0.98 0.99 1.05
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Step 4: ETRETOH 2.exeStep 4: ETRETOH 2.exe
Calculate ETrs & ETos using ETHgrv
Input File– DataT&P.prn from XXX COAG.xls
Latitude, Tmax, Tmin, Tavg– COEFHRGV.dat
Monthly Coefficient all Station (15 max.)
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Step 4: COEFHGRV.datStep 4: COEFHGRV.dat
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Step 4: ETRETOH 2.exeStep 4: ETRETOH 2.exe
Calculation of ETrs & ETos using 1985 Hargreaves
ETrs = COEF x ETHgrv (Daily) ETos = COEF1 x ETHgrv (Daily)
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ameano RTTTET )8.17()(0023.0 5.0minmax
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Step 4: Final ResultsStep 4: Final Results
Year, DOY, Month, Day, ETrs,ETos, Precip.
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Apr May Jun Jul Aug Sep0
1
2
3
4
5
6
7
8
9 Ft Morgan ETrs
ETrs ETrs Est
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Apr May Jun Jul Aug Sep0
1
2
3
4
5
6
7
8 Center ETrs
ETrs ETrs Est
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Apr May Jun Jul Aug Sep0
2
4
6
8
10
12 Yuma2 ETrs
ETrs ETrs Est
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Apr May Jun Jul Aug Sep0
2
4
6
8
10
12
Rocky Ford ETrs
ETrs ETrs Est
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Apr May Jun Jul Aug Sep0
2
4
6
8
10
12Avondale ETrs
ETrs ETrs Est
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Apr May Jun Jul Aug Sep0
2
4
6
8
10
12 Fruita ETrs
ETrs ETrs Est
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Apr May Jun Jul Aug Sep0
1
2
3
4
5
6
7
8
9
10Yellow Jacket ETrs
ETrs ETrs Est
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FRT01
PTV01 0
PAN01 0
ORM01 4
YUM01 8
YJK01 18
IDL01 18
HYK02 18
CTZ01 18
HEB01 0.3
COW01 0.4
SCM01 1.4
GLY04 1.5
BRL03 1.7
STT01 1.8
PBL01 1.8
ILF01 1.9
HRT01 2.7
LAM02 2.9
STN01 3.7
STG01 3.7
CDG01 3.8
LJR01 4.1
WLT01 4.4
LAM04 4.6HLY02 4.6LMS01 4.8LJT01 4.8
FWL01 4.8
WFD01 5.1
CTR02 6.2
RFD02 6.5
YUC01 7.3
LAM03 7.4
BRG01 7.4
WGG01 7.6
PAI01 8.2
HLY01 8.2
WGG02 8.3
SAN01 9.4
EAC01 9.4
HNE01 9.8TWC01 11.5
HOT01 11.6
BLA01 11.6
HXT01 12.7
LAM01 13.4
YUM02 13.6WRY01 13.6
KRK01 13.6
FTM01 14.7
DLT01 14.7
GJC01 15.6
CTR01 16.2
VLD01 16.4
DVC01 17.1
OTH01 17.4
BRL02 17.4FRT02 17.5
RFD01 17.5AVN01 17.5
AKR02 17.5
KSY01 17.6
FTC03 17.6
BRL01 17.6
LCN01 17.8
FTL01 17.8
ALT01 17.8
FTC01 17.9
CoAgMet Stations
Years
0 - 4
5 - 7
8 - 11
12 - 14
15 - 18
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Process -- Historical ETref EstimatesProcess -- Historical ETref Estimates
CoAgMet Data XXX COAG.xls -- QC for Good data Colcrbt2.exe -- Cal’c Monthly Hgrv
Factors ETRETOH 2.exe - Calculate ETrs & ETos
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Meadow Grass ET
Review of Methods Recommendation for Calculation ETc
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Reported ProceduresReported Procedures
SCS –BC Pasture Grass– 10% / 1,000 m. change in elevation– ASCE Manual 70 does not recommend
Pochop Method -- ASAE 1984– Limited to Alfalfa (9%) & Turf (6%)– Adjusted kt --- thus not true SCS BC– Adjust from elevation Coefficient derived– Wyoming
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Reported ProceduresReported Procedures
Denver Water Board, BC “k” coef.– South Park, Elev. 8,900 ft msl– Standard BC not modified BC– Local calibration– ET calculated as:
Lysimeter water use + Precipitation (100%)
– ETirr wtr = ETc - Precipitation
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Recommend Transferrable Kc Recommend Transferrable Kc
Smith’s Gunnison basin – Hargreaves Monthly Coefficients– Letter Describing included in Materials
Maly & Walter – Kc’s Meadow Grass– Memo Describing process included in Materials
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Hargreaves Kc’s for Meadow GrassHargreaves Kc’s for Meadow Grass
Multiple Sites -- 5 years of data May = 1.16 June = 1.28 July = 1.04 August = 0.86 September = 0.88
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Meadow Grass Kc -- Derived using Calibrated Hargreaves
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Software & Documents ProvidedSoftware & Documents Provided
XXX COAG.xls -- QC data Colcrbt2.exe -- Calc’ Monthly Coef. ETRETOH 2.exe -- Calc’ ETrs & ETos Example Input and Output files Memo: Coefficients for Meadow Grass Smith Letter: Hargreaves Kc M.Grass Daily Ra calculation Application
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FRT01
PTV01 0
PAN01 0
ORM01 4
YUM01 8
YJK01 18
IDL01 18
HYK02 18
CTZ01 18
HEB01 0.3
COW01 0.4
SCM01 1.4
GLY04 1.5
BRL03 1.7
STT01 1.8
PBL01 1.8
ILF01 1.9
HRT01 2.7
LAM02 2.9
STN01 3.7
STG01 3.7
CDG01 3.8
LJR01 4.1
WLT01 4.4
LAM04 4.6HLY02 4.6LMS01 4.8LJT01 4.8
FWL01 4.8
WFD01 5.1
CTR02 6.2
RFD02 6.5
YUC01 7.3
LAM03 7.4
BRG01 7.4
WGG01 7.6
PAI01 8.2
HLY01 8.2
WGG02 8.3
SAN01 9.4
EAC01 9.4
HNE01 9.8TWC01 11.5
HOT01 11.6
BLA01 11.6
HXT01 12.7
LAM01 13.4
YUM02 13.6WRY01 13.6
KRK01 13.6
FTM01 14.7
DLT01 14.7
GJC01 15.6
CTR01 16.2
VLD01 16.4
DVC01 17.1
OTH01 17.4
BRL02 17.4FRT02 17.5
RFD01 17.5AVN01 17.5
AKR02 17.5
KSY01 17.6
FTC03 17.6
BRL01 17.6
LCN01 17.8
FTL01 17.8
ALT01 17.8
FTC01 17.9
CoAgMet Stations
Years
0 - 4
5 - 7
8 - 11
12 - 14
15 - 18