bb_slope is read from parameter file, but overwritten prior to use

[rgknox]

Summary of Issue:

bb_slope (stomatal slope, as per BBF photosynthesis lore) is read from the parameter file, indexed by PFT. This parameter is supposedly used by EDPhotosynthesis. The parameter file value is stored in bb_slope, and it is transferred to mbb. bb_slope is used no-where else in the code.

Around line 360:

            ! Soil water stress applied to Ball-Berry parameters
            do FT = 1,numpft_ed
               if (nint(c3psn(FT)) == 1)then
                  ps = 1
               else
                  ps = 2
               end if
               bbb(FT) = max (bbbopt(ps)*currentPatch%btran_ft(FT), 1._r8)

               mbb(FT) = bb_slope(ft) ! mbbopt(ps)
            end do

So bb_slope is used to populate mbb. However mbb is then over-written in the next patch loop, and had not been used prior to the over-write. At roughly 404 of EDPhotosynthesis:

      do f = 1,fn
         p = filterp(f)
         c = patch%column(p)
         s = hsites(c)

         if (patch%is_veg(p)) then

            currentPatch => map_clmpatch_to_edpatch(sites(s), p) 

            do FT = 1,numpft_ed
               if (nint(c3psn(FT)) == 1)then
                  ps = 1
               else
                  ps = 2
               end if
               bbb(FT) = max (bbbopt(ps)*currentPatch%btran_ft(FT), 1._r8)
               mbb(FT) = mbbopt(ps)           # FIX POINT

               if (nint(c3psn(FT)) == 1)then
                  ci(:,FT,:) = 0.7_r8 * cair(p)
               else
                  ci(:,FT,:) = 0.4_r8 * cair(p)
               end if
            enddo

Where you can see above, that the actual parameters being used are two values from Gordon Bonan's paper. Not that those values aren't reasonable, but we should decide where we want the values set.

As far as I can tell, these are values for C3 and C4 pathways.

The two values are 9 (C3 I think) and 4 (C4), the paper is Bonan et al. 2011, JGR, 116, doi: 10.1029/2010JG001593

I think what happened is that when bb_slope was added to the code as a user controlled parameter, the coder just didn't see that the mbb variable was set twice. It actually isn't used in the first appearance.

My recommendation is that we simply remove the first call to mbb and bb_slope, and change the line I flagged "FIX POINT" to:

mbb(FT) = bb_slope(ft)

Have discussed this issue with @xuchongang

What is the changeset ID of the code, and the machine you are using:

all to current

[ckoven]

would explain the surprising lack of a bb_slope effect in Elias and @xuchongang's sensitivity study?

[rgknox]

yeah, I stumbled across some old notes I had on this, and combined with their results, prompted me to revisit the code

[rosiealice]

Yeah, this was just re-engineered in CLM5. You're correct on all counts. It
should come from the file...
On Jun 7, 2016 18:11, "Ryan Knox" [email protected] wrote:

yeah, I stumbled across some old notes I had on this, and combined with
their results, prompted me to revisit the code

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[rgknox]

ok, its a simple fix, sounds like we are all in agreement

[rgknox]

There is another parameter that is somewhat coupled in with the slope parameter:

Ball-Berry minimum leaf conductance, unstressed (umol H2O/m**2/s).

Is this cuticular?

We are using some two values hard-coded for C3 and C4 plants. Is there interest in adding these as PFT parameters to the parameter file?

@rosiealice , @xuchongang , others?

[xuchongang]

Ryan,
Thank you very much for identify this issue and suggest the correction.
Yes, it would be great if we could have the cuticular conductance as an
input parameter as it is important for our plant hydraulic models. We have
measurement data on that.

Yours
Chonggang

On Tue, Jun 14, 2016 at 2:14 PM, Ryan Knox [email protected] wrote:

There is another parameter that is somewhat coupled in with the slope
parameter:

Ball-Berry minimum leaf conductance, unstressed (umol H2O/m**2/s).

Is this cuticular?

We are using some two values hard-coded for C3 and C4 plants. Is there
interest in adding these as PFT parameters to the parameter file?

@rosiealice https://github.com/rosiealice , @xuchongang
https://github.com/xuchongang , others?

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[rosiealice]

Actually, this would be great. Danica has a paper on the impact of minimum
stomatal conductance in GMDD at the moment, based evidence it's larger that
it's larger than these hardwired numbers...

On 14 June 2016 at 15:24, chonggang xu [email protected] wrote:

Ryan,
Thank you very much for identify this issue and suggest the correction.
Yes, it would be great if we could have the cuticular conductance as an
input parameter as it is important for our plant hydraulic models. We have
measurement data on that.

Yours
Chonggang

On Tue, Jun 14, 2016 at 2:14 PM, Ryan Knox [email protected]
wrote:

There is another parameter that is somewhat coupled in with the slope
parameter:

Ball-Berry minimum leaf conductance, unstressed (umol H2O/m**2/s).

Is this cuticular?

We are using some two values hard-coded for C3 and C4 plants. Is there
interest in adding these as PFT parameters to the parameter file?

@rosiealice https://github.com/rosiealice , @xuchongang
https://github.com/xuchongang , others?

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Dr Rosie A. Fisher

Terrestrial Sciences Section
Climate and Global Dynamics
National Center for Atmospheric Research
1850 Table Mesa Drive
Boulder, Colorado, 80305
USA.
+1 303-497-1706

http://www.cgd.ucar.edu/staff/rfisher/

[rgknox]

applied corrections, PR to come, testing