Difference between revisions of "Evapotranspiration"

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Line 28: Line 28:
| - 0.372 || - 0.232 || - 0.035 || 0.171 || 0.330 || 0.407 || 0.372 || 0.239 || 0.052 || - 0.157 || - 0.325 || - 0.407
| - 0.372 || - 0.232 || - 0.035 || 0.171 || 0.330 || 0.407 || 0.372 || 0.239 || 0.052 || - 0.157 || - 0.325 || - 0.407
|-
|-
! Day length (hr) || 9 || 10 || 12 || 13 || 15 || 15 || 15 || 14 || 12 || 11 || 9 || 9
! Day length (hr)  
| 9 || 10 || 12 || 13 || 15 || 15 || 15 || 14 || 12 || 11 || 9 || 9
|-
|-
! Temperature (°C) || - 6.20 || - 4.90 || - 0.30 || 6.90 || 13.30 || 18.70 || 21.40 || 20.30 || 15.90 || 9.10 || 3.10 || - 2.70
! Temperature (°C)  
| - 6.20 || - 4.90 || - 0.30 || 6.90 || 13.30 || 18.70 || 21.40 || 20.30 || 15.90 || 9.10 || 3.10 || - 2.70
|-
|-
! Monthly heat index, i || 0.00 || 0.00 || 0.00 || 1.63 || 4.40 || 7.37 || 9.04 || 8.34 || 5.76 || 2.48 || 0.48 || 0.00
! Monthly heat index, i  
| 0.00 || 0.00 || 0.00 || 1.63 || 4.40 || 7.37 || 9.04 || 8.34 || 5.76 || 2.48 || 0.48 || 0.00
|-
|-
! PET (mm, uncorrected) || 0.00 || 0.00 || 0.00 || 29.91 || 62.44 || 91.50 || 106.44 || 100.33 || 76.28 || 40.80 || 12.19 || 0.00
! PET (mm, uncorrected)  
| 0.00 || 0.00 || 0.00 || 29.91 || 62.44 || 91.50 || 106.44 || 100.33 || 76.28 || 40.80 || 12.19 || 0.00
|-
|-
! days in month || 31 || 28 || 31 || 30 || 31 || 30 || 31 || 31 || 30 || 31 || 30 || 31
! days in month  
| 31 || 28 || 31 || 30 || 31 || 30 || 31 || 31 || 30 || 31 || 30 || 31
|-
|-
! Corrected PET (mm) || 0.0 || 0.0 || 0.0 || 33.1 || 78.3 || 116.4 || 136.9 || 119.3 || 78.7 || 38.1 || 9.6 || 0.0
! Corrected PET (mm)  
| 0.0 || 0.0 || 0.0 || 33.1 || 78.3 || 116.4 || 136.9 || 119.3 || 78.7 || 38.1 || 9.6 || 0.0
|}
|}

Revision as of 16:59, 8 January 2018

Calculation[edit]

Thornthwaite Mather method[edit]

Step 1. Calculate the monthly heat index (i): where: T = mean monthly temperature.

Step 2. Calculate the annual heat index (I):

Step 3. Calculate an uncorrected Potential Evapotranspiration (PETuncorrected):

where: α = 6.75 x 10-7 I3 - 7.71 x 10-5 I2+ 0.0179 I + 0.49

Step 4. A monthly correction is then applied to account for varying daylight hours and number of days in a month, to find the corrected potential evapotranspiration (PET):

Example[edit]

For the town of Richmond Hill (Lat = 43.87)

Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec
Declination (rad) - 0.372 - 0.232 - 0.035 0.171 0.330 0.407 0.372 0.239 0.052 - 0.157 - 0.325 - 0.407
Day length (hr) 9 10 12 13 15 15 15 14 12 11 9 9
Temperature (°C) - 6.20 - 4.90 - 0.30 6.90 13.30 18.70 21.40 20.30 15.90 9.10 3.10 - 2.70
Monthly heat index, i 0.00 0.00 0.00 1.63 4.40 7.37 9.04 8.34 5.76 2.48 0.48 0.00
PET (mm, uncorrected) 0.00 0.00 0.00 29.91 62.44 91.50 106.44 100.33 76.28 40.80 12.19 0.00
days in month 31 28 31 30 31 30 31 31 30 31 30 31
Corrected PET (mm) 0.0 0.0 0.0 33.1 78.3 116.4 136.9 119.3 78.7 38.1 9.6 0.0

The quantity of water transpired (given off). Retained in plant tissues, and evaporated from plant tissues and surrounding soil surfaces. Quantitatively it is usually expressed in terms of depth of water per unit area during a specified period. e.g. mm/day

The combined loss of water to the atmosphere from land and water surfaces by evaporation and from plants by transpiration.

The quantity of water transpired (given off). Retained in plant tissues, and evaporated from plant tissues and surrounding soil surfaces. Quantitatively it is usually expressed in terms of depth of water per unit area during a specified period. e.g. mm/day

The combined loss of water to the atmosphere from land and water surfaces by evaporation and from plants by transpiration.

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