The following code produces a graph with monthly ET from 2001-2015 over a region.
In contrast, when plotting the daily data,
exporting to excel and summing up the daily values to get monthly values, the results change significantly.
e.g. January 2001: 33 mm (resulting from the first code) and 57 mm (result of the sum of 8-day values manually with excel, picture).
The study area is the same, does anyone know where the problem is?