Option to overwrite runoff with prescribed runoff for certain regions

[ekluzek]

This is something needed for the TU Delft project. I'm putting it in here partially to see if there might be some interest in it long term.

This is a note from @billsacks on a discussion we had with Miren V. on how to do this.

Let's keep this relatively simple and say: Overwrite runoff over all of Greenland (overwrite both vegetated and glacier columns, so we can just work with gridcell-level values); overwrite the full liquid and solid runoff (i.e., overwrite all components of the runoff so we end up using the complete runoff from the prescribed values over this domain – including, for example, rain that runs off from vegetated surfaces).
We'll initially produce cpl hist files from about 20 years of run that could be cycled through. We suggest writing 3-hourly averages from the coupler. Then CLM could read this in as a stream and overwrite the lnd → cpl fields just over the Greenland domain, as determined by the glacier area mask.

The namelist control for this would be to turn it on or off, and then also which glacier region(s) to operate over. For present day there are a total of four regions: inland Greenland, outer Greenland and possible ice shelves for Greenland, Antarctica, and everything else.

For the Delft project this needs to go on the release branch.

[ekluzek]

This does need to be done in the release version. Here's some notes I've found on this from email:

A paper on the simulation to compare to...

https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2019MS002031

I think this corresponds to this simulation with Ice Sheet on:

b.e21.B1850G.f09_g17_gl4.CMIP6-piControl-withism.001

see

https://csegweb.cgd.ucar.edu/experiments/public/

Here's a note from Bill:

The next priority will be one-way coupling. Within this, the priority is the overwriting of CLM's runoff fluxes. It's important that this be done in the CESM2.1 code base. Getting this into CTSM master (main long-term development branch) is not a high priority. So Erik will work on getting this CLM runoff-overwriting implemented (possibly in a quick and dirty way if it will save significant time) in the CESM2.1 code base. We'll check in at that point to talk about the plan for overwriting CISM's runoff fluxes (note that, since we're using 2.1, a NUOPC-based data model is not an option, so anything we do for that is likely to be relatively short-lived).

[ekluzek]

Runoff sent to the coupler includes lnd2atmType terms:

surface:
qflx_rofliq_qsur_grc + qflx_rofliq_h2osfc_grc
subsurface:
qflx_rofliq_qsub_grc + qflx_rofliq_drain_perched_grc
ice:
qflx_rofice_grc

History terms: QRUNOFF_TO_COUPLER(qflx_rofliq_grc), QRUNOFF_ICE_TO_COUPLER(qflx_rofice_grc)
qflx_rofliq_grc subtracts out qflx_liq_dynbal_grc (transient flux)

There's a glacier, lake, wetland residual term as well, and the transient land change flux

qflx_rofliq_grc comes from qflx_roflig_col which comes from qflx_runoff

qflx_runoff: is in HydrologyDrainageMod.F90
qflx_runoff(c) = qflx_drain(c) + qflx_surf(c) + qflx_h2osfc_surf(c) + qflx_qrgwl(c) + qflx_drain_perched(c)
In history those terms are: QDRAI (qflx_drain), QOVER (qflx_surf), QH2OSFC(qflx_h2osfc_surf), QRGWL(qflx_qrgwl), QDRAI_PERCH(qflx_drain_perched)

[ekluzek]

Looks like this should be a modification of SurfaceRunoff in SoilHydrologyMod.F90. So the namelist items to control the stream files would be in SoilHydReadNML which uses the namelist: soilhydrology_inparm. The streams handling could be additional subroutines part of SoilHydrologyMod.F90.

This work is started on my fork on the prescribed_glc_runoff branch.

[ekluzek]

Miren V. pointed me to the following in an email:

I recently contacted Leo van Kampenhout as he prescribed Greenland freshwater fluxes for a paper with CESM1.

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2015GL064738

He shared a couple of scripts he used. As a first guess, he thinks it could be done similarly for CESM2.

[ekluzek]

This work is started and on my prescribed_glc_runoff branch. So

https://github.com/ekluzek/CTSM/tree/prescribed_glc_runoff