irrigate in 1850 is off for runs with use_crop but on for those without

[billsacks]

Brief summary of bug

Irrigation seems to be turned on for all non-crop runs, including year-1850 runs. I would expect irrigation to be off in non-crop year-1850 runs, just like it's off in year-1850 runs with use_crop.

General bug information

CTSM version you are using: ctsm1.0.dev011

Does this bug cause significantly incorrect results in the model's science? Yes

Configurations affected: Non-crop year-1850 runs

Details of bug

Irrigation is turned off for crops in year-1850. I would expect the same to be true for non-crop runs. Instead, it appears that irrigation is turned on in all non-crop runs, even for year 1850. This means that the generic crop is split into irrigated vs. unirrigated in these runs.

It's possible that this is intentional, but this seemed weird to @ekluzek and me.

Important details of your setup / configuration so we can reproduce the bug

I noticed this by looking through various tests in the aux_clm test suite.

Important output or errors that show the problem

I checked user_nl_clm and, for one test (ERP_Ld5.f10_f10_musgs.I1850Clm50Bgc.cheyenne_gnu.clm-default), confirmed that PCT_CFT indicates that there is truly non-zero area of the irrigated generic crop.

[billsacks]

@dlawrenncar @olyson do you know if this is intentional?

[ekluzek]

An important detail here is that the SP datasets all include irrigated generic crop. So if you have it split out into irrigated generic crop -- can you really turn irrigation off? I suppose setting "irrigate=.false." in this case just means that the irrigated and rainfed CFT's will be separate, but act the same way. So I guess that's OK, so we could turn it off.

I think we want to assess what this should look like though.

[billsacks]

I'm struggling to see why SP vs. BGC should matter here, since non-crop runs use the same subgrid structure whether they're using SP or BGC (but that may be my lack of understanding).

I do notice that, currently, the collapsing is only done when use_crop is true:

https://github.com/ESCOMP/ctsm/blob/a0ca27c1f67c2d544cfc490a23986cf35247d393/src/main/surfrdMod.F90#L788-L790

I think that, if we can assume that create_crop_landunit is always true (which is the case now, right?) then that should always be called - otherwise, setting irrigate to false won't accomplish anything.

But my understanding here is less than complete, so it's possible that I'm misspeaking....

[olyson]

I would think that irrigation should be off for non-crop 1850 runs as well. I don't think it being on is intentional.

[ekluzek]

From looking at the code (inside of collapse_crop_types), I don't think this will work right now. And I'm pretty sure that's how it ended up the way it is. It should work on the branch that @slevisconsulting is working on in PR #483. So we can change it after that comes to master.

I'm planning on doing a simple test for this when I get a chance to document how it fails. So I'm not 100% sure this is the case, but I'm 95% sure, and we can easily test it.

[billsacks]

@dlawrenncar feels that, really, we should have irrigation on in 1850 for all configurations. @ekluzek , @dlawrenncar and I can't remember why we decided to turn it off in 1850, but we might have notes somewhere on it. It might have just been a performance issue.

For CESM2.1, we're going to leave this as is. For beyond that, we'll probably change this so that irrigation is always on.

[billsacks]

From a quick search of past meeting notes, the closest I found to a rationale for having irrigation off in 1850 was a reference to this old bugzilla issue: http://bugs.cgd.ucar.edu/show_bug.cgi?id=2476

Dave's comment there was:

Just about everything except the 1850 simulations should have irrigation on as default. I will continue to work to get the message out about the cost that running with irrigation incurs.

which suggests that performance was the main reason for this, though it's not 100% clear.

[billsacks]

Ah, I just found this bugzilla issue which is very similar to the current issue: http://bugs.cgd.ucar.edu/show_bug.cgi?id=2479

Our conclusion here is consistent with the one there: Let's wait for the ability to collapse crop types from a 78 pft dataset down to one without crops; then it will be easier to make crop and non-crop consistent in this respect.

[billsacks]

Here are the relevant lines:

<!-- Irrigation default -->
<irrigate use_crop=".true." phys="clm5_1"  use_cndv=".false." sim_year_range="1850-2100">.true.</irrigate>
<irrigate use_crop=".true." phys="clm5_1"  use_cndv=".true."  sim_year_range="1850-2100">.false.</irrigate>
<irrigate use_crop=".true." phys="clm5_0" use_cndv=".false."  sim_year_range="1850-2100">.true.</irrigate>
<irrigate use_crop=".true." phys="clm5_0" use_cndv=".true."   sim_year_range="1850-2100">.false.</irrigate>
<irrigate use_crop=".true." phys="clm4_5"                     sim_year_range="1850-2100">.false.</irrigate>

<irrigate use_crop=".true." >.false.</irrigate>
<irrigate use_crop=".false.">.true.</irrigate>

What we'll do is remove the last line, and remove all use_crop attributes from all lines - so the behavior is the same for use_crop true and false. Note that this will change answers for clm5_0, but we're okay with this.