Add new submodule for an alternate ROF model WRF-Hydro

[ekluzek]

There is a team working on coupling WRF-Hydro into CTSM, CAM, and CESM. @rcabell @scrasmussen @felfelan among others.

The repository is here:

https://github.com/NCAR/wrf_hydro_nwm_public

In the shorter term we will bring this into CTSM as a new submodule. Longer term we may have it as a package that's built with mizuRoute. But, we'll have to see how that works.

NOTE: WE WILL NOT INCLUDE THIS IN THE RELEASE BRANCH for cesm3_0. So we will need to either have a branch for this or remove it on the release branch. I suggest the latter since it's lower overhead. We just need to remember to do it.

Definition of Done:

• Figure out how the WRF-Hydro NUOPC cap will work in coupling into CESM
• Figure out what tests we will want to have for it
• Figure out how to get it to build in the CESM system
• Add it to the submodules in .gitmodules in a PR to bring into master
• Add some tests for it in the initial PR
• Add a PR into CMEPS to pass the additional fields needed
• PR to bring in new CMEPS and new tests that extend the functionality

[ekluzek]

@rcabell and @scrasmussen there are a couple questions/options in how this could be done. First, is that it might take a while to get it working, so we either create a branch for this, or we bring in small bits incrementally that start adding the new capability. Second, is that either CIME/CESM specific stuff needs to go into the WRF-Hydro repository, OR we create an interface repository for this kind of thing.

On the first, I think I'd like to bring in small bits incrementally that go onto our b4b-dev branch, and that we show the regular CTSM doesn't change answers. Then there isn't an additional branch that has to be maintained outside of our normal workflow.

On the second. It might be clearer to have the interface repository for this. Examples of this are:

https://github.com/ESCOMP/CISM-wrapper

Or MOM-Interface in ESCOMP as well.

The main things that would exist there are directories like this:

cime_config -- includes scripts to interface with CIME to build the library and to create input files to run it
src/CPL/cesm_cpl/nuopc ------- NUOPC cap code to interface with the CESM coupler for the ROF component, including rof_comp_nuopc.F90

I think both of these would interact with existing WRF-Hydro code and scripts to do the things that CESM/CIME needs from it. It looks like the CESM NUOPC cap code would probably just be a wrapper code on top of your NUOPC caps you have under src/CPL.

On the CTSM side, WRF-Hydro would show up in a directory under "components", alongside the other ROF components. So you'd have:

components/mosart
components/rtm
components/mizuRoute

and then in addition something like:

components/wrf_hydro_nwm