Error in ch4Mod with transient land use

[jiamengl]

Hi,

I met an error while running a case with transient land use. I am running ctsm5.1.dev098, the case is 2000_DATM%GSWP3v1_CLM50%BGC-CROP_SICE_SOCN_MOSART_SGLC_SWAV, with Carbon isotope on.

Below is my setting of surface data and landuse timeseries.

fsurdat = '/glade/p/cesmdata/cseg/inputdata/lnd/clm2/surfdata_map/release-clm5.0.18/surfdata_1.9x2.5_hist_78pfts_CMIP6_simyr1850_c190304.nc'
flanduse_timeseries= '/glade/p/cesmdata/cseg/inputdata/lnd/clm2/surfdata_map/landuse.timeseries_1.9x2.5_hist_78pfts_CMIP6_simyr1850-2015_c170824.nc'

The error message is:
Methane demands exceed methane available. Error in methane competition (mol/m^3
676: /s), c,j: -1.400621840730309E-010 3 1
676: Latdeg,Londeg= 36.9473684210525 240.000000000000

ERROR: Methane demands exceed methane available.ERROR in ch4Mod.F90 at line 36

I have revised the code, but it can run without any errors if without landuse timeseries; I also tried the case with transient landuse timeseries but without any change to the code, it can also succeed. My edits of the code is mainly in PhotosynthesisMod.F90, I guess the issue is probably about the change of Carbon flux related to land use change, but I couldn't figure out why the error occurs in ch4Mod.F90, as I didn't change this F90 code.
I attached the cesm.log file for your reference. Your help is greatly appreciated.

 

[oleson]

Changes in one area of the code can certainly affect other areas of the code, particularly if the inputs to that code have changed and/or are unrealistic. We have seen errors crop up in the methane model due to seemingly unrelated changes in other parts of the code, so the behavior you describe isn't unusual.
There is some indication of problems earlier in the log file:

76: Note: sink > source in ch4_tran, sources are changing quickly relative to diff
676: usion timestep, and/or diffusion is rapid.
676: Latdeg,Londeg= 36.9473684210525 240.000000000000
676: This typically occurs when there is a larger than normal diffusive flux.
676: If this occurs frequently, consider reducing land model (or methane model) tim
676: estep, or reducing the max. sink per timestep in the methane model.

So, you could consider shortening the time step, although if you are running the typical 1/2 hour time steps then the model should behave properly. I'm not clear on how to reduce the max sink per timestep.
That said, I don't have any specific suggestions as to how to troubleshoot this other than to think about what inputs to the methane model you've changed through your code mods.
If methane isn't the focus of your research, I *think* you can simply turn it off (use_lch4=.false.), it should be independent of the rest of the model (in other words, you should get the same results for non-methane variables with it on or off).