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STEP BY STEP CALCULATION DAILY EVAPOTRANSPIRATION ( ETo ) EXAMPLE

STEP BY STEP CALCULATION DAILY EVAPOTRANSPIRATION ( ETo ) EXAMPLE. PENMAN-MONTEITH METHOD FAO PAPER NO. 56 Komariah , PhD. Given Information. Date : July 6, 2011 Location: UNS : 7 o 33’ S Elevation: 100 m asl T max : 21.5 o C T min : 12.3 o C. RH max: 84% RH min: 63%

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STEP BY STEP CALCULATION DAILY EVAPOTRANSPIRATION ( ETo ) EXAMPLE

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  1. STEP BY STEP CALCULATIONDAILY EVAPOTRANSPIRATION (ETo)EXAMPLE PENMAN-MONTEITH METHOD FAO PAPER NO. 56 Komariah, PhD.

  2. Given Information • Date : July 6, 2011 • Location: UNS : 7o33’ S • Elevation: 100 m asl • T max : 21.5 oC • T min : 12.3oC • RH max: 84% • RH min: 63% • Wind speed at 10 m : 10 km/h  2.78 m/s • Sunshine: 9.25 hours Q: Determine Eto ???

  3. EQUATION

  4. Step : 1 • Determine T as T mean: T = (T max + T min )/ 2 T = (21.5 + 12.3)oC / 2 = 16.9 oC

  5. Step 2 : • Determine 

  6. Or, use Table 2.2

  7. Step: 3 • Determine ∆

  8. Or, use Table 2.4 • Interpolation  ∆ = 0.122 kPa/oC

  9. Step 4: • Determine u2 from

  10. Or, use Table 2.9 • u2 = 2.78 x 0.748 = 2.078 m/s

  11. Step 5: • Determine es from

  12. Or, use Table 2.3 • es = (2.564 + 1.431) /2 = 1.997 kPa

  13. Step 5: • Determine ea from •  ea = 1.409 kPa

  14. Step 6: • Determine G from

  15. Step 7: • Determine Rn from

  16. Step 7-1:

  17. Step 7-1-1: Recommendation: a= 0.25 and b= 0.50

  18. Step 7-1-1-1: Or, Use Table 2.6

  19. Interpolation, Ra = 30.9 MJ m-2 d-1

  20. Step 7-1-1-2: Or, Use Table 2.7

  21. Interpolation, N = 11.63 hours

  22. …Back to Step 7-1-1: Recommendation: a= 0.25 and b= 0.50 Calculate, Rs = 20.01 MJ m-2 d-1

  23. … Back to Step 7-1: Calculate, Rns = 15.41 MJ m-2 d-1

  24. Step 7-2: Step 7-2-1: Use Table 2.8

  25. T min : 12.3; Interpolate   = 32.56 MJ/m2 d T max : 21.5;   = 36.96 MJ/m2 d Calculate = 34.76 MJ m-2 d-1

  26. Step 7-2-2: Calculate, Rso = 23.24 MJ m-2 d-1

  27. … Back to Step 7-2: CalculateRnl = 4.91 MJ m-2 d-1

  28. … Back to Step 7: • Determine Rn from CalculateRn = 10.50 MJ m-2 d-1

  29. Step 8 (FINAL): CalculateETo = 3.29 mm d-1

  30. Crop Evapotranspiration (ETc)  Crop Water Requirement

  31. ETc = Kc x ETo

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