Handling of Shape Parameter bsw_col in organic matter mixing

[jjokella]

Currently bsw organic matter mixing is hard-coded according to Cosby et al. (1984) Table 5 formula:

eCLM/src/clm5/biogeophys/SoilStateInitTimeConstMod.F90

Line 465 in 7853ec4

soilstate_inst%bsw_col(c,lev) = (1._r8-om_frac) * (2.91_r8 + 0.159_r8*clay) + om_frac*om_b

In dev-perturbation, when parameters are read in from file, the read-in value are used instead:

eCLM/src/clm5/biogeophys/SoilStateInitTimeConstMod.F90

Line 567 in b80fe6d

soilstate_inst%bsw_col(c,lev) = (1._r8-om_frac) * soilstate_inst%bsw_col(c,lev) + om_frac*om_b

Discussion point

Should we change the default from the hard-coded Cosby-equation to using input parameters?

Status in CTSM

Still hard-coded, new: scale parameter in front:

https://github.com/ESCOMP/CTSM/blob/2c44dbeb6e00b1012d0f0fef3daa43848b4da15b/src/biogeophys/SoilStateInitTimeConstMod.F90#L554-L555

[kvrigor]

Should we change the default from the hard-coded Cosby-equation to using input parameters?

Definitely doable in code, but I think the change must be based from a scientific POV. That equation is described in the Soil water hydraulic properties section (Eq. 2.7.52) of the CLM Tech Note. Basically any change should remain consistent with the assumptions of soil water transport calculations implemented in CLM5/eCLM.