The problem of understanding output variables of CLM.

[XinhaoSuo]

Hi~
I was running an I2000CLM50CN experiment recently and had a problem with the results.
I first ran this experiment for ten years, and found that FCO2 presents a process from negative to positive. FCO2 is the value CO2 flux to atmosphere (+ to atm), so I think it is a net CO2 flux.
While soil is generally regarded as a carbon sink, so this value should be negative. Although the model may not be fully spin up, the positive trend of this value is robust, so how to understand the phenomenon that FCO2 is positive?

 

[oleson]

You can investigate what may be contributing to that behavior by tracking down the variable in the code that corresponds to FCO2:

call hist_addfld1d(fname='FCO2', units='kgCO2/m2/s', &
avgflag='A', &
long_name='CO2 flux to atmosphere (+ to atm)', &
ptr_lnd=this%net_carbon_exchange_grc, &
default='inactive')

net_carbon_exchange is the negative of nbp_grc (net biome production). So then you can track down the components of npb_grc.

 

[XinhaoSuo]

Thanks for your reply. I think it may be caused by the lack of spin-up. I will try this case again.

You can investigate what may be contributing to that behavior by tracking down the variable in the code that corresponds to FCO2:

call hist_addfld1d(fname='FCO2', units='kgCO2/m2/s', &
avgflag='A', &
long_name='CO2 flux to atmosphere (+ to atm)', &
ptr_lnd=this%net_carbon_exchange_grc, &
default='inactive')

net_carbon_exchange is the negative of nbp_grc (net biome production). So then you can track down the components of npb_grc.