Changes

===Thornthwaite Mather method===

===Thornthwaite Mather method===

The Thornthwaite Mather method of calculating water balance<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> is recommended within the [https://www.ontario.ca/document/stormwater-management-planning-and-design-manual 2003 Ontario Stormwater Management Planning and Design Manual].

The Thornthwaite Mather method of calculating water balance<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> is recommended within the [https://www.ontario.ca/document/stormwater-management-planning-and-design-manual 2003 Ontario Stormwater Management Planning and Design Manual]. The original paper (linked below) provides the required calculations as a series of lookup tables. The following equations are derived from these, and are widely documented elsewhere.

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

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

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