Changes

==Calculation==

==Calculation==

===Thornthwaite Mather method <ref>Thornthwaite, C. W., and Mather, J. R., Instructions and Tables for Computing Potential Evapotranspiration and the Water Balance, Drexel Institute of Technology, Laboratory of Climatology, 1957.{{#l:Thornthwaite1957.pdf}}</ref>===

===Thornthwaite Mather method===<ref>Thornthwaite, C. W., and Mather, J. R., Instructions and Tables for Computing Potential Evapotranspiration and the Water Balance, Drexel Institute of Technology, Laboratory of Climatology, 1957.{{#l:Thornthwaite1957.pdf}}</ref>

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: 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):

'''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>