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>

<math>\alpha=6.75\times10^{-7}I^{3}-7.71\times10^{-5}I^{2}+0.0179I+0.49</math>

<math>\alpha=6.75\times10^{-7}I^{3}-7.71\times10^{-5}I^{2}+0.0179I+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>