LAI of C3 grass is zero

[Heng Yan]

Hi, I am using CLM5.0 for a single-point simulation. I created the surface data and atmospheric forcing data myself. The PFT at this site is C3 grassland, but when I output the LAI, I found that the LAI was zero throughout the 1000-year spinup period.
I also checked LEAFC and GPP, and their values are zero as well. I noticed that in the CNVegCarbonStateType.F90 code of CLM, the LEAFC of grassland is initialized to 0, while the LEAFC of evergreen vegetation is initialized to initial_vegC. I changed the initial LEAFC of non-evergreen vegetation in the code to 5, and then the LAI could be output normally. However, I am not sure if this modification is reasonable.
At the same time, I also tried changing the grassland to a needleleaf evergreen tree in a temperate climate, and I found that the LAI could also be output normally.
I really want to know how to solve this problem. The files below are my surface data 、atmforcing and parameter settings.

Heng Yan

 

[slevis]

That's great that you tried a few things and addressed the problem. To me, the first solution seems more appropriate than the second, because in the first you just changed initial LEAFC, while in the second you represented the C3 grass with a tree (if I understood correctly).

Another thought:
I wonder whether you completed a spin-up phase in your simulation. If not, I also wonder whether it makes sense for your case. To decide, please read this section of the User's Guide:

1.5.5. Spinup of CLM5.0-BGC-Crop — ctsm release-clm5.0 documentation

If you decide to run a spin-up, the model will set initial LEAFC for you.

 

[Heng Yan]

That's great that you tried a few things and addressed the problem. To me, the first solution seems more appropriate than the second, because in the first you just changed initial LEAFC, while in the second you represented the C3 grass with a tree (if I understood correctly).

Another thought:
I wonder whether you completed a spin-up phase in your simulation. If not, I also wonder whether it makes sense for your case. To decide, please read this section of the User's Guide:

1.5.5. Spinup of CLM5.0-BGC-Crop — ctsm release-clm5.0 documentation

If you decide to run a spin-up, the model will set initial LEAFC for you.

Thanks for Slevis, I tried changing the initial LEAFC to 5 and ran a 500-year spinup, but after 20 years of the spinup, LEAF quickly dropped from 5 to 0, and TOTECOSYSC also quickly decreased to 0. I output AR, GPP and NEP, and found that NEP was always negative because GPP was less than AR. I don't know what the problem is. In the end, I decided to use SP for the simulation and then calculate GPP using the output FPSN and TLAI. I created my lai stream file for my case.

 

[slevis]

If that works for you, that's great. I just wanted to follow up though:
If you did not run a proper BGC Spin-up (see User's Guide link that I shared earlier), then you may lose all the LEAFC due to lack of spun up nitrogen in the soil.