The water budget for cells located in surface water bodies need to be calculated on a monthly basis.

[jnsebgosselin]

Currently, for cells located in surface water bodies, we calculate the water budget on a yearly basis only.

Basically, we take a constant value for the yearly evaporation from a map* and subtract this constant value to the annual precipitation. The results is stored as surface runoff.

There is no reason not to use our input data to actually calculate monthly values for each cell located in surface water bodies, except the lack of time to do it...

• Ministère des Pêches et de l’Environnement du Canada, Service de l’environnement at-mosphérique, 1975. Atlas hydrologique du Canada. http://ftp.geogratis.gc.ca/pub/nrcan_rncan/raster/atlas/fra/hydro_1978/water_quantity_temperature_winds/17_Evaporation_Annuelle_Moyenne_Eaux_Lacustres_1978_150.pdf [accédé en mars 2018].

[jnsebgosselin]

This cause problem with the post-processing of outputs, because HELP produces results on a monthly basis, while we compute the surface water cells on a yearly basis...

Moreover, this prevent us from being able to compute monthly water budget that take into account evaporation from free water cells.

[jnsebgosselin]

Here are some resources that can be useful to address this issue:

https://github.com/woodcrafty/PyETo
http://python.hydrology-amsterdam.nl/moduledoc/index.html#module-evaplib
http://python.hydrology-amsterdam.nl/modules/evaplib.py