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Model : Thornthwaite
Simile version : 3.1+
Date added : 2003-09-06
Keywords : Evapotranspiration ;
Model to calculate potential evaporation (PET) using the Thornthwaite method. Thornthwaite (1944) defines potential evaporation as “the water loss which will occur if at no time there is a deficiency of water in the soil for use of vegetation.” — assuming soil storage is not depleted.
Input files and results for Leuchars, Scotland 56 degrees N, and Boston, USA 54 degrees N, are supplied.
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Potential evapo-transpiration (mm/day), PET = if Ta > 0 then dl*16*(10*Ta/I)^a else 0 where Ta is mean monthly temperature (Celsius) a = 0.49+0.0179*I-7.71*10^ -5*I^2+6.75*10^ -7*I^3 dl = daylength in hours / 12 I = sum(i) i is a monthly heat index given by i = if Ta>0 then (Ta/5)^1.5 else 0
PET, Ta and dl for Boston, USA (in blue) and Leuchars, Scotland (in red).|
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