Calibration for Historical Crop ET Estimates A Process

EVAPOTRANSPIRATION WORKSHOP Calibration for Historical Crop ET Estimates A Process Ivan A. Walter, P.E. Ivan s Engineering, Inc. 1

Kc ETstzd vs SCS BC Kc ET stzd is more accurate than SCS BC Kc -- Generate from measurement at known sites Kc -- Transferrable ET stzd ET professional & researchers have accepted td SCS BC Crop Coefficients derived where??? SCS BC Requires local l calibration i 2

Why Isn t Kc ET Used stzd Answers A to Why not? SCS BC is well accepted in Colo. Water Court. Do not have the data for ET stzd Do not have the Kc s 3

What is Desirable Result Just J tsome number for ETc Accurate daily Temp, Rs, U, & Rh Accurate daily ET rs & ET os Accurate monthly ET rs & ET os Excel lfil files &Programs for analysis 4

Criteria (ASCE Task Committee) Understandable Defensible Simplification without loss of accuracy Based on & Traceable to Experimental Data 5

Rocky Ford ETrs 12 10 ETrs ETrs Est 8 6 4 2 0 Apr May Jun Jul Aug Sep 6

Rocky Ford: Est as % of Actual 110% ETrs Est /: ETrs ETos Est / ETos 105% 100% 95% 90% 85% 80% May Jun Jul Aug Sep 7

Fort Morgan -- 2005 Daily Data 0.6 ETrs 0.5 ETrs Est 0.4 inches 0.3 0.2 0.1 0 1-Apr 1-May 1-Jun 1-Jul 1-Aug 1-Sep 1-Oct 8

Raw Data >>>>>> ETc Download data from Web site QC the data Select good data Calc ET rs, ET os, and ET Hrgv Calibration Calc s with good data COEF Hgrv x ET Hrgv = ET rs COEF1 Hgrv x ET Hrgv = ET os 9

Begin Here Standardized Reference ET Equation: ET ref C n 0.408 ( Rn G) u 2 ( es e T 273 (1 C d u 2 ) a ) 10

Begin Here w/ Data from Web 11

Calculate & Analyze & Compare Standardized Reference ET Equation: ET ref C n 0.408 ( Rn G ) u 2 ( es e T 273 (1 C d u 2 ) a ) 1985 Hargreaves Equation: ET o 0.0023( T Tmin) ) max min 0.5 ( T mean 17.8) R a 12

Final Product Standardized di d Reference ET values Short Crop: ETos Tall Crop: ETrs Daily values 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 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 15

Step 3: Colcrbt2.exe -- Results Linear Regression Analysis (daily) Zero intercept Monthly Ratio: ET rs to ET Hgrv Monthly Ratio: ET os to ET Hgrv Monthly Ratio: ET rs to ET os Regression Coef & SEE 16

Step 3 Results: Ratio ET rs : ET Hrgv MAY JUN JUL AUG SEP Fort Morgan(Tdpt Adjusted) 1995 2006 1.40 1.36 1.27 1.25 1.37 Fort Collins 03 1999 2006 1.48 1.41 1.38 1.38 1.56 Center 1996 2006 1.54 1.38 1.15 1.18 1.47 Avondale 1994 2008 1.30 1.33 1.22 1.16 1.22 Rocky Ford 1994 2008 1.32 1.36 1.22 1.17 1.17 Yuma 1996 2006 1.58 1.54 1.34 1.28 1.47 Fruita 1999 2006 1.34 1.28 1.15 1.13 1.21 Yellow Jacket 1992 2008 1.31 1.29 1.22 1.24 1.36 17

Results @ Center: Ratio ET rs :ET Hrgv MAY JUN JUL AUG SEP All 154 1.54 138 1.38 115 1.15 118 1.18 147 1.47 1996 1.68 1.25 1.06 1.14 1.47 1997 1.31 1.32 1.16 1.06 1.25 1998 1.62 1.56 1.08 1.15 1.48 1999 1.56 1.43 1.09 1.12 1.38 2000 143 1.43 130 1.30 111 1.11 117 1.17 157 1.57 2001 1.45 1.35 1.07 1.15 1.52 2002 1.56 1.36 1.15 1.23 1.34 2003 1.50 1.38 1.21 1.17 1.48 2004 1.61 1.38 1.23 1.37 1.56 2005 1.54 1.44 1.24 1.26 1.57 2006 1.57 1.43 1.17 1.15 1.47 18

Step 3 Results: Ratio ET os : ET Hrgv MAY JUN JUL AUG SEP Fort Morgan(Tdpt Adjusted) 1995 2006 1.02 1.01 0.96 0.96 1.00 Fort Collins 03 1999 2006 1.07 1.03 1.03 1.03 1.10 Center 1996 2006 1.15 1.06 0.93 0.94 1.09 Avondale 1994 2008 1.03 1.01 0.94 0.93 0.99 Rocky Ford 1994 2008 1.04 1.04 0.94 0.94 0.95 Yuma 1996 2006 1.14 1.13 1.03 0.99 1.07 Fruita 1999 2006 1.00 0.97 0.90 0.88 0.91 Yellow Jacket 1992 2008 1.01 1.01 0.98 0.99 1.05 19

Step 4: ETRETOH 2.exe Calculate ET rs & ET os using ET Hgrv Input File DataT&P.prn from XXX COAG.xls Latitude, Tmax, Tmin, Tavg COEFHRGV.dat Monthly Coefficient all Station (15 max.) 20

Step 4: COEFHGRV.dat 21

Step 4: ETRETOH 2.exe Calculation of ET rs & ET os using 1985 Hargreaves ET rs = COEF x ET Hgrv (Daily) ET os = COEF1 x ET Hgrv (Daily) ET o 0.0023( 0023( T max T min ) 0.5 ( T mean 17.8) R a 22

Step 4: Final Results Year, DOY, Month, Day, ETrs,ETos, ETos Precip. 23

9 8 7 6 5 4 3 2 1 ETrs ETrs Est Ft Morgan ETrs 0 Apr May Jun Jul Aug Sep 24

8 7 Center ETrs ETrs ETrs Est 6 5 4 3 2 1 0 Apr May Jun Jul Aug Sep 25

12 Yuma2 ETrs 10 ETrs ETrs Est 8 6 4 2 0 Apr May Jun Jul Aug Sep 26

Rocky Ford ETrs 12 10 ETrs ETrs Est 8 6 4 2 0 Apr May Jun Jul Aug Sep 27

12 Avondale ETrs 10 ETrs ETrs Est 8 6 4 2 0 Apr May Jun Jul Aug Sep 28

12 Fruita ETrs 10 ETrs ETrs Est 8 6 4 2 0 Apr May Jun Jul Aug Sep 29

10 Yellow Jacket ETrs 9 8 7 6 5 4 3 2 1 ETrs ETrs Est 0 Apr May Jun Jul Aug Sep 30

CoAgMet Stations 8-11 Years 12-14 0-4 5-7 15-18 COW01 0.4 HEB01 0.3 WFD01 5.1 FTC03 17.6WLT01 4.4 ALT01 17.8BRG01 7.4 LCN01 17.8 FTC01 17.9 GLY04 1.5 KSY01 17.6 WGG02 8.3 WGG01 7.6 FTM01 14.7 PTV01 0 FTL01 17.8 ILF01 1.9 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 FRT02 17.5 FRT01 GJC01 15.6 ORM01 4 CDG01 3.8 PAN01 0 HOT01 11.6 DLT01 14.7 OTH01 17.4 STN01 3.7BRL03 1.7 BRL02 17.4 SCM01 1.4 DVC01 17.1 YJK01 18 CTR02 6.2 CTR01 16.2 VLD01 16.4PBL01 1.8 LAM04 4.6LAM02 2.9 FWL01 4.8 LJT01 4.8 LMS01 4.8 HLY02 4.6 AVN01 17.5RFD02 6.5 LAM03 7.4 HLY01 8.2 RFD01 17.5 LAM01 13.4 YUC01 7.3CTZ01 18 TWC01 11.5 BLA01 11.6 LJR01 4.1 SAN01 9.4 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 ET rs & ET os 32

Meadow Grass ET Review of Methods Recommendation for Calculation ETc 33

Reported Procedures SCS BC Pasture Grass 10% / 1,000 m. change in elevation ASCE Manual al 70 does not recommend Pochop Method -- ASAE 1984 Limited i to Alfalfa (9%) & Turf (6%) Adjusted kt --- thus not true SCS BC Adjust from elevation Coefficient derived Wyoming 34

Reported Procedures Denver er 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%) ET irr wtr = ETc - Precipitation 35

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 36

Hargreaves Kc s for Meadow Grass Multiple Sites -- 5 years of data May = 1.16 June = 1.28 Jl July = 104 1.04 August = 0.86 September = 0.88 37

Meadow Grass Kc Derived using Calibrated Hargreaves 38

Software & Documents Provided XXX COAG.xls -- QC data Colcrbt2.exe -- Calc Monthly Coef. ETRETOH 2.exe -- Calc ET rs & ET os Example Input and Output files Memo: Coefficients for Meadow Grass Smith Letter: Hargreaves Kc MGrass M.Grass Daily Ra calculation Application 39

CoAgMet Stations 8-11 Years 12-14 0-4 5-7 15-18 COW01 0.4 HEB01 0.3 WFD01 5.1 FTC03 17.6WLT01 4.4 ALT01 17.8BRG01 7.4 LCN01 17.8 FTC01 17.9 GLY04 1.5 KSY01 17.6 WGG02 8.3 WGG01 7.6 FTM01 14.7 PTV01 0 FTL01 17.8 ILF01 1.9 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 FRT02 17.5 FRT01 GJC01 15.6 ORM01 4 CDG01 3.8 PAN01 0 HOT01 11.6 DLT01 14.7 OTH01 17.4 STN01 3.7BRL03 1.7 BRL02 17.4 SCM01 1.4 DVC01 17.1 YJK01 18 CTR02 6.2 CTR01 16.2 VLD01 16.4PBL01 1.8 LAM04 4.6LAM02 2.9 FWL01 4.8 LJT01 4.8 LMS01 4.8 HLY02 4.6 AVN01 17.5RFD02 6.5 LAM03 7.4 HLY01 8.2 RFD01 17.5 LAM01 13.4 YUC01 7.3CTZ01 18 TWC01 11.5 BLA01 11.6 LJR01 4.1 SAN01 9.4 HNE01 9.8 STT01 1.8 40