Difference between revisions of "Evapotranspiration"

From LID SWM Planning and Design Guide
Jump to navigation Jump to search
Line 5: Line 5:
where:
where:
T = mean monthly temperature.  
T = mean monthly temperature.  


Step 2. Calculate the annual heat index (I):
Step 2. Calculate the annual heat index (I):
Line 14: Line 13:


where: α = 6.75 x 10<sup>-7</sup> ''I<sup>3</sup>'' - 7.71 x 10<sup>-5</sup> ''I<sup>2</sup>''+ 0.0179 ''I'' + 0.49
where: α = 6.75 x 10<sup>-7</sup> ''I<sup>3</sup>'' - 7.71 x 10<sup>-5</sup> ''I<sup>2</sup>''+ 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):
<math>PET=PET_{uncorrected}\cdot\frac{N}{12}\cdot\frac{daylight\ hours}{30}</math>

Revision as of 16:27, 8 January 2018

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):