Changes

We are in the process of writing an xls tool to semi-automate these; please feel free request a draft copy, or to contribute your own [[How to contribute]].  

We are in the process of writing an xls tool to semi-automate these; please feel free request a draft copy, or to contribute your own [[How to contribute]].  

'''Step 1.''' Calculate the monthly heat index (i):

'''Step 1.''' Calculate the monthly heat index ('i'):

<math>i=\left ( \frac{T}{5} \right )^{1.514}</math>

<math>i=\left ( \frac{T}{5} \right )^{1.514}</math>

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'):

<math>I=\sum_{i=1}^{12}i</math>

<math>I=\sum_{i=1}^{12}i</math>

'''Step 3.''' Calculate an uncorrected Potential Evapotranspiration (PET_uncorrected):

'''Step 3.''' Calculate an uncorrected Potential Evapotranspiration ('PET_uncorrected'):

<math>PET_{uncorrected}=16\cdot \left ( \frac{10\cdot T}{I} \right )^{\alpha }</math>

<math>PET_{uncorrected}=16\cdot \left ( \frac{10\cdot T}{I} \right )^{\alpha }</math>

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

where:  

<math>α = 6.75 x 10^-7 ''I³'' - 7.71 x 10^-5 ''I²''+ 0.0179 ''I'' + 0.49</math>

'''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):

'''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>

<math>PET=PET_{uncorrected}\cdot\frac{N}{12}\cdot\frac{daylight\ hours}{30}</math>