Add rainfall, glaciermelt, and snowmelt as output variables

[PeterNelemans]

Feature type

Adding new functionality

Improvement Description

Currently, rainfall, glaciermelt and snowmelt cannot be written to output. It is possible to write rainfallplusmelt to output, which is the sum of the three aformentioned variables, but you cannot write the individual components to output.

Optionally, maybe allow for snowfall to be added to the output as well?

Implementation Description

Allow for rainfall, glaciermelt and snowmelt (and potentially snowfall) to be added to the output section of your toml, and let Wflow write these variables to netCDF and/or CSV.

Additional Context

Together with @cvanstrien, @jaapschellekens and @tanerumit I was working on a wflow_sbm model of the Vakhsh catchment in Tajikistan. The client was interested in knowing the different contributions of rainfall, snowmelt, and glaciermelt to the overal discharge. However, we couldn't easily extract these contributions from Wflow. Luckily, @JoostBuitink made a branch of Wflow which allows for these variables to be added to the output. It would be nice if these changes were also added to the main

[verseve]

These variables are available now in the Master branch as part of refactoring work (as part of variables or boundary_conditions). Related issue for mapping of these variables: #481.