===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>
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===Thornthwaite Mather method===
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The Thornthwait 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 [2003 Ontario Stormwater Management Planning and Design Manual https://www.ontario.ca/document/stormwater-management-planning-and-design-manual]
'''Step 1.''' Calculate the monthly heat index (i):
'''Step 1.''' Calculate the monthly heat index (i):