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EVAPOTRANSPIRATION WORKSHOP
Calibration for Historical
Crop ET Estimates – A Process
Ivan A. Walter, P.E.
Ivan’s Engineering, Inc.
3/12/2010
Ivan A. Walter, P.E.
1
Kc ETstzd vs SCS BC
Kc ETstzd is more accurate than SCS BC
–
–
–
–
–
3/12/2010
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
Ivan A. Walter, P.E.
2
Why 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
3/12/2010
Ivan A. Walter, P.E.
3
What 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
3/12/2010
Ivan A. Walter, P.E.
4
Criteria (ASCE Task Committee)
Understandable
Defensible
Simplification
without loss of accuracy
Based on & Traceable to Experimental
Data
3/12/2010
Ivan A. Walter, P.E.
5
Rocky Ford ETrs
12
10
ETrs
ETrs Est
8
6
4
2
0
Apr
3/12/2010
May
Jun
Ivan A. Walter, P.E.
Jul
Aug
Sep
6
Rocky Ford: Est as % of Actual
110%
ETrs Est /: ETrs
ETos Est / ETos
105%
100%
95%
90%
85%
80%
May
3/12/2010
Jun
Jul
Ivan A. Walter, P.E.
Aug
Sep
7
Fort Morgan -- 2005 Daily Data
0.6
ETrs
0.5
ETrs Est
inches
0.4
0.3
0.2
0.1
0
1-Apr
3/12/2010
1-May
1-Jun
1-Jul
1-Aug
Ivan A. Walter, P.E.
1-Sep
1-Oct
8
Raw 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
3/12/2010
Ivan A. Walter, P.E.
9
Begin Here
Standardized Reference ET Equation:
ETref
3/12/2010
Cn
0.408 ( Rn G)
u 2 (e s e a )
T 273
(1 C d u 2 )
Ivan A. Walter, P.E.
10
Begin Here w/ Data from Web
3/12/2010
Ivan A. Walter, P.E.
11
Calculate & Analyze & Compare
Standardized Reference ET Equation:
ETref
Cn
0.408 ( Rn G)
u 2 (e s e a )
T 273
(1 C d u 2 )
1985 Hargreaves Equation:
ETo 0.0023(Tmax Tmin )
3/12/2010
Ivan A. Walter, P.E.
0.5
(Tmean 17.8) Ra
12
Final Product
Standardized Reference ET values
–
–
–
3/12/2010
Short Crop: ETos
Tall Crop: ETrs
Daily values
Ivan A. Walter, P.E.
13
Step 1: XXX COAG.xls
Download data
from COAGMet site
QC
the data
– Identify the Good Data
– Fix small gaps & errors
– Throw out everything else
3/12/2010
Ivan A. Walter, P.E.
14
Step 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
3/12/2010
Ivan A. Walter, P.E.
15
Step 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
3/12/2010
Ivan A. Walter, P.E.
16
Step 3 Results: Ratio ETrs : ETHrgv
Fort Morgan(Tdpt Adjusted)
1995 - 2006
Fort Collins 03 1999 - 2006
Center 1996 - 2006
Avondale 1994 - 2008
Rocky Ford 1994 -2008
Yuma 1996 - 2006
Fruita 1999 2006
Yellow Jacket 1992 - 2008
3/12/2010
MAY
JUN
JUL
AUG
SEP
1.40
1.48
1.54
1.30
1.32
1.58
1.34
1.31
1.36
1.41
1.38
1.33
1.36
1.54
1.28
1.29
1.27
1.38
1.15
1.22
1.22
1.34
1.15
1.22
1.25
1.38
1.18
1.16
1.17
1.28
1.13
1.24
1.37
1.56
1.47
1.22
1.17
1.47
1.21
1.36
Ivan A. Walter, P.E.
17
Results @ Center: Ratio ETrs : ETHrgv
All
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
3/12/2010
MAY
1.54
1.68
1.31
1.62
1.56
1.43
1.45
1.56
1.50
1.61
1.54
1.57
JUN
1.38
1.25
1.32
1.56
1.43
1.30
1.35
1.36
1.38
1.38
1.44
1.43
JUL
1.15
1.06
1.16
1.08
1.09
1.11
1.07
1.15
1.21
1.23
1.24
1.17
Ivan A. Walter, P.E.
AUG
1.18
1.14
1.06
1.15
1.12
1.17
1.15
1.23
1.17
1.37
1.26
1.15
SEP
1.47
1.47
1.25
1.48
1.38
1.57
1.52
1.34
1.48
1.56
1.57
1.47
18
Step 3 Results: Ratio ETos : ETHrgv
Fort Morgan(Tdpt Adjusted)
1995 - 2006
Fort Collins 03 1999 - 2006
Center 1996 - 2006
Avondale 1994 - 2008
Rocky Ford 1994 -2008
Yuma 1996 - 2006
Fruita 1999 2006
Yellow Jacket 1992 - 2008
3/12/2010
MAY
JUN
JUL
1.02
1.07
1.15
1.03
1.04
1.14
1.00
1.01
1.01
1.03
1.06
1.01
1.04
1.13
0.97
1.01
0.96
1.03
0.93
0.94
0.94
1.03
0.90
0.98
Ivan A. Walter, P.E.
AUG
0.96
1.03
0.94
0.93
0.94
0.99
0.88
0.99
SEP
1.00
1.10
1.09
0.99
0.95
1.07
0.91
1.05
19
Step 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
3/12/2010
Station (15 max.)
Ivan A. Walter, P.E.
20
Step 4: COEFHGRV.dat
3/12/2010
Ivan A. Walter, P.E.
21
Step 4: ETRETOH 2.exe
Calculation of
ETrs & ETos using 1985
Hargreaves
ETrs = COEF x ETHgrv
(Daily)
ETos = COEF1 x ETHgrv (Daily)
ETo 0.0023(Tmax Tmin )
3/12/2010
Ivan A. Walter, P.E.
0.5
(Tmean 17.8) Ra
22
Step 4: Final Results
Year, DOY, Month, Day, ETrs,ETos, Precip.
3/12/2010
Ivan A. Walter, P.E.
23
Ft Morgan ETrs
9
ETrs
8
ETrs Est
7
6
5
4
3
2
1
0
3/12/2010
Apr
May
Jun
Ivan A. Walter, P.E.
Jul
Aug
Sep
24
Center ETrs
8
ETrs
ETrs Est
Aug
Sep
7
6
5
4
3
2
1
0
Apr
3/12/2010
May
Jun
Jul
Ivan A. Walter, P.E.
25
Yuma2 ETrs
12
ETrs
10
ETrs Est
8
6
4
2
0
Apr
3/12/2010
May
Jun
Jul
Ivan A. Walter, P.E.
Aug
Sep
26
Rocky Ford ETrs
12
ETrs
ETrs Est
10
8
6
4
2
0
Apr
3/12/2010
May
Jun
Ivan A. Walter, P.E.
Jul
Aug
Sep
27
Avondale ETrs
12
ETrs
ETrs Est
10
8
6
4
2
0
Apr
3/12/2010
May
Jun
Jul
Ivan A. Walter, P.E.
Aug
Sep
28
Fruita ETrs
12
ETrs
ETrs Est
10
8
6
4
2
0
Apr
3/12/2010
May
Jun
Jul
Ivan A. Walter, P.E.
Aug
Sep
29
Yellow Jacket ETrs
10
9
ETrs
8
ETrs Est
7
6
5
4
3
2
1
0
Apr
3/12/2010
May
Jun
Jul
Ivan A. Walter, P.E.
Aug
Sep
30
CoAgMet Stations
8 - 11
Years
12 - 14
15 - 18
0-4
5-7
COW01 0.4
ILF01 1.9
HEB01 0.3
WFD01 5.1
FTC03 17.6WLT01 4.4
ALT01 17.8BRG01 7.4
LCN01 17.8
GLY04 1.5
FTC01 17.9
KSY01 17.6 WGG02 8.3WGG01 7.6
FTM01 14.7
PTV01 0
FTL01 17.8
HXT01 12.7
HYK02 18
PAI01 8.2
STG01 3.7
WRY01 13.6
YUM02 13.6
YUM01 8
AKR02 17.5
HRT01 2.7
EAC01 9.4
IDL01 18
KRK01 13.6
BRL01 17.6
STN01 3.7BRL03 1.7
BRL02 17.4
FRT02 17.5
FRT01
GJC01 15.6ORM01 4
CDG01 3.8
DLT01 14.7
PAN01 0
HOT01 11.6
OTH01 17.4
SCM01 1.4
VLD01 16.4PBL01 1.8
LAM04 4.6LAM02 2.9
FWL01 4.8
HLY02 4.6
LJT01 4.8
LMS01 4.8
AVN01 17.5RFD02 6.5
HLY01 8.2
LAM03 7.4
RFD01 17.5
LAM01 13.4
DVC01 17.1
CTR02 6.2
CTR01 16.2
YJK01 18
BLA01 11.6
YUC01 7.3CTZ01 18
TWC01 11.5
3/12/2010
LJR01 4.1
SAN01 9.4
Ivan A. Walter, P.E.
HNE01 9.8
STT01 1.8
31
Process -- 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
3/12/2010
Ivan A. Walter, P.E.
32
Meadow Grass ET
Review of Methods
Recommendation for Calculation ETc
3/12/2010
Ivan A. Walter, P.E.
33
Reported Procedures
SCS
–
–
–BC Pasture Grass
10% / 1,000 m. change in elevation
ASCE Manual 70 does not recommend
Pochop Method -- ASAE 1984
–
–
–
–
3/12/2010
Limited to Alfalfa (9%) & Turf (6%)
Adjusted kt --- thus not true SCS BC
Adjust from elevation Coefficient derived
Wyoming
Ivan A. Walter, P.E.
34
Reported 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
–
3/12/2010
water use + Precipitation (100%)
ETirr wtr = ETc - Precipitation
Ivan A. Walter, P.E.
35
Recommend Transferrable Kc
Smith’s
–
–
Gunnison basin
Hargreaves Monthly Coefficients
Letter Describing included in Materials
Maly & Walter – Kc’s Meadow Grass
–
3/12/2010
Memo Describing process included in Materials
Ivan A. Walter, P.E.
36
Hargreaves 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
3/12/2010
Ivan A. Walter, P.E.
37
Meadow Grass Kc -- Derived using Calibrated Hargreaves
3/12/2010
Ivan A. Walter, P.E.
38
Software & 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
3/12/2010
Ivan A. Walter, P.E.
39
CoAgMet Stations
8 - 11
Years
12 - 14
15 - 18
0-4
COW01 0.4
ILF01 1.9
5-7
HEB01 0.3
WFD01 5.1
FTC03 17.6WLT01 4.4
ALT01 17.8BRG01 7.4
LCN01 17.8
GLY04 1.5
FTC01 17.9
KSY01 17.6 WGG02 8.3WGG01 7.6
FTM01 14.7
PTV01 0
FTL01 17.8
HXT01 12.7
HYK02 18
PAI01 8.2
STG01 3.7
WRY01 13.6
YUM02 13.6
YUM01 8
AKR02 17.5
HRT01 2.7
EAC01 9.4
IDL01 18
KRK01 13.6
BRL01 17.6
STN01 3.7BRL03 1.7
BRL02 17.4
FRT02 17.5
FRT01
GJC01 15.6ORM01 4
CDG01 3.8
DLT01 14.7
PAN01 0
HOT01 11.6
OTH01 17.4
SCM01 1.4
VLD01 16.4PBL01 1.8
LAM04 4.6LAM02 2.9
FWL01 4.8
HLY02 4.6
LJT01 4.8
LMS01 4.8
AVN01 17.5RFD02 6.5
HLY01 8.2
LAM03 7.4
RFD01 17.5
LAM01 13.4
DVC01 17.1
CTR02 6.2
CTR01 16.2
YJK01 18
BLA01 11.6
YUC01 7.3CTZ01 18
TWC01 11.5
3/12/2010
LJR01 4.1
SAN01 9.4
Ivan A. Walter, P.E.
HNE01 9.8
STT01 1.8
40