Fix rutter interception

[verseve]

Issue addressed

Fixes #299

Explanation

The amount of computed throughfall and stemflow in the modified Rutter interception model could become larger than the precipitation input (water balance issue), because the sum of the stemflow partitioning coefficient pt and free throughfall coefficient p could get larger than 1. In addition, the net interception (netinterception) was not computed correctly: the first drainage term dd was subtracted from precipitation (as part of throughfall), while dd is controlled by a change in the canopy storage capacity cmax over time (e.g. because of a change in leaf area index LAI), and thus not part of the precipitation input. This could result in a negative netinterception:

netinterception = precipitation - throughfall - stemflow

Finally, the interception (interception loss through evaporation) output from the modified Rutter interception model should be stored in SBM, and not netinterception. The interception loss through evaporation is used to compute total actual evapotranspiration (actevap).

Checklist

• Branch is up to date with master
• Tests & pre-commit hooks pass
• Updated documentation if needed
• Updated changelog.md if needed

[JoostBuitink]

Thanks for addressing this issue; the proposed changes look good to me! I have made some small changes to the names of the variables, in order to make the code a bit more readable. Let me know if you agree with these changes or not!

[verseve]

I have made some small changes to the names of the variables, in order to make the code a bit more readable. Let me know if you agree with these changes or not!

I agree with the changes to the variable names!