I've been running some single-point CLM-SP and FATES-SP experiments at Toolik (with only one pft - c3 arctic grass) and have noticed that there are large differences in snow depth between the CLM and FATES runs. Comparing with the NEON observations of net radiation at this site, the CLM-SP results look pretty good. It seems like this issue is likely due to a difference in how grasses are buried by snow in CLM.

Below is the FATES code describing the fraction exposed vegetation:

And the parallel code in CLM, which allows for "snow burial fraction for short vegetation (e.g. grasses, crops) changes with vegetation height using a 20% bending factor, as used in Lombardozzi et al. (2018) GRL 45(18), 9889-9897"

        ! NOTE: The following snow burial code is duplicated in CNVegStructUpdateMod.
         ! Changes in one place should be accompanied by similar changes in the other.

         if (patch%itype(p) > noveg .and. patch%itype(p) <= nbrdlf_dcd_brl_shrub ) then
            ol = min( max(snow_depth(c)-hbot(p), 0._r8), htop(p)-hbot(p))
            fb = 1._r8 - ol / max(1.e-06_r8, htop(p)-hbot(p))
         else
            fb = 1._r8 - (max(min(snow_depth(c),max(0.05,htop(p)*0.8_r8)),0._r8)/(max(0.05,htop(p)*0.8_r8)))
         endif

Here is a time series and climatology of snow depth from a CLM-SP run, which looks as expected:

And corresponding results from the FATES-SP run:

Should FATES include a similar bending factor for grasses as is being used in CLM?

@wwieder @adrifoster @ckoven @jenniferholm