default root zone depth of the CESM

[hongru]

Hello, I'm a new user and want to use the output of the CESM with the CLM5.

I just have a simple question about the variable 'BTRAN2', which is the root zone soil wetness factor.
I just want to confirm the depth of the root zone in the CESM is 0-0.5m(as written in Lawrence et al. 2019 or others?

standard/"MOAR"	component	temporal frequency	variable name	time averaging	long name	units	dimensions
lnd	std	month_1	BTRAN2	time: mean	root zone soil wetness factor	unitless	time lat lon

 

[oleson]

If you are referring to this in the Lawrence paper:

"SMRT is the e-folding decay timescale of soil moisture due to evapotranspiration and is an integrative measure of soil-plant-atmosphere dynamics. We calculate SMRT for the root zone (0–0.5 m) from daily soil moisture curves during post-rain periods using a procedure similar to the estimation of a base flow recession constant (Vogel & Kroll, 1996). This residence time metric is reflective of the evapotranspiration dry-down response timescale (Teuling et al., 2006)."

I think the 0.5m was just set to calculate SMRT.

BTRAN2 is a separate root zone soil moisture for the fire model only.

If the plant hydraulic stress (PHS) model is on, the default in CLM5, then BTRAN will be the soil moisture stress from PHS. In the context of PHS, BTRANMN, the daily minimum of BTRAN, is probably more meaningful.

In CLM5, the fraction of roots in each soil layer and hence the rooting depth varies with plant functional type. See the following explanation in the technical note:

2.11. Plant Hydraulics — ctsm release-clm5.0 documentation