Pass lake Precip and ET as optional fields

[ekluzek]

We need to pass Precipitation minus Evapotranspiration from the LND (CTSM) model to ROF (mizuRoute) over lakes. We need to add an XML variable in CMEPS to determine if it's going to be passed so that both CTSM and mizuRoute can know it's being passed.

The CTSM issue is here:

ESCOMP/CTSM#1206

[ekluzek]

I suggest the xml variable be called something like: FLDS_LAKE_SURF_H2O_BAL. The mediator changes in CMEPS are to add the field descriptor to mediator/fd_cesm.yaml, and add it to the fields list to ROF in mediator/esmFldsExchange_cesm_mod.F90. The mediator will pass it if both LND and ROF want it. CTSM and mizuRoute will decide to send/receive it if the xml variable FLDS_LAKE_SURF_H2O_BAL is set. This likely means that they each will have an additional namelist item to determine if it should be sent/received.

This is a task for me to do. But, I don't have permission to assign to to myself.

[ekluzek]

We will pass these as two separate fields so they can do more analysis in mizuRoute, and it will just be over lake areas.