The usage of the frac_nobio variable in ORCHIDEE

frac_nobio is the variable which describes the fraction of the grid box which will never (in the foreseeable future !) be covered by vegetation. These fraction can be covered by glaciers, cities lakes or any other surface type where no biological activity (transpiration, assimilation, decomposition, ...) will happen. For the moment only glaciers are considered.

Thus the grid box within ORCHIDEE is devided into fractions of no-bio and veget with the following property : 1 = SUM(frac_nobio(:,jn), jn=1,nnobio) + SUM(veget_max(:,jv), jv=1,nvm)

This variable has 2 dimensions : kjpindex and nnobio. In other words, the number of land grid points in ORCHIDEE and the number of no-bio classes. For the moment nnobio=1.

In the following we will go through each of the modules and detail where frac_nobio is used and with which intention.

general comments

the 2 variables frac_nobio and totfrac_nobio are passed to most subroutines. This is redundant information as in principle totfrac_nobio(:) = SUM(frac_nobio(:,jn), jn=1,nnobio). Nowhere is it verified that the this is indeed true and in case of the DVGM activated it will certainly not be the case.

The addition of the second dimension to frac_nobio (nnobio) was not done correctly and is not fully implemented.

A first step in an effort to better handle the no-bio fraction would be to clean-up the code and terminate the implementation of the nnobio dimension. Only frac_nobio should be used and the implementation of the second dimension should be finished.

slowproc

slowproc_veget :

• computes the frac_nobio from the vegetation map read. It sums all the fractions which are covered by ice in carteveg5km.nc.
• AD: defines soiltile(:,jst=1,3) for hydrol. totfrac_nobio(:) is included in soiltile(:,1), the fraction covered by bare soil (PFT1, jv=1).

slowproc_readvegetmax : derived from the PFT map as the complement needed to bring the sum of veget(ig,jv) to 1. So the other types of non biological active surface types are apparently not documented in the PFT maps.

stomate_main : also returns a new total frac_nobio (totfrac_nobio_new) in case of a dynamic vegetation.

In case totfrac_nobio changes (which can occur through stomate_main) there is no code to adjust frac_nobio. Thus a divergence between these two variables will be created.

There is no code either to update all the prognostic variables of the model which depend on frac_nobio, does this matter ?

condveg

In condveg the frac_nobio is used in the same way as veget in order to derive surface properties.

condveg_snow : uses frac_nobio to add the albedo of ice to the total albedo of the grid box. Should other nobio types be present the model will stop. So only frac_nobio for ice is foreseen for the moment.

condveg_z0logz and condveg_z0cdrag : use the same logic as for the snow and compute the grid box average surface roughness taking into account the properties of the ice (z0_nobio).

diffuco

Ensures that over the frac_nobio only sublimation can occur.

diffuco_snow : in this subroutine vbetaveg1 will be modified assuming that the all frac_nobio types have sublimation.

enerbil

Here frac_nobio is not used. The information about the fraction of the grid box which is not covered by vegetation or bare soil is integrated in the various surface parameters provided to enerbil (vbeta1, soilflx, soilcap).

AD: do the energy and water and fluxes produced by enerbil correspond to vegtot= SUM(veget_max(:,jv), jv=1,nvm), or to vegtot+totfrac_nobio=1 ??

hydrol

hydrol_snow : frac_nobio is used to update the snow mass with the fraction of sublimation attributable to the fraction of the grid not covered by biological active surfaces. It also intervenes in the melting of the snow on (1-totfrac_nobio) and split the falling snow over the 2 sub areas of the grid box.

AD: hydrol_soil treats the soil water balance with the following features, which may not be consistent from the point of view of nobio:

• the soil treated in hydrol_soil covers SUM(soiltile(ji,:))=1=vegtot+totfrac_nobio
• excluding the water fluxes to/from the routing scheme for simplicity, the soil receives as liquid input fluxes: (i) the snowmelt that was produced from vegtot+totfrac_nobio, and (ii) the rainfall that fell on vegtot only. Here, I am not sure if it's consistent to redistribute this rainfall on vegtot+totfrac_nobio without renormalization...?
• the water fluxes that leave the soil are (i) the surface runoff, drainage, and bare soil evaporation (evapnu), which are produced over SUM(soiltile(ji,:))=vegtot+totfrac_nobio, (ii) the transpiration and interception loss, which are only produced from the PFT 2 to nvm, corresponding to soiltile(ji,2)+soiltile(ji,3). This sends back to my question regarding enerbil, although I don't imply this is wrongly done in the code.

AD: a point that raises doubt on the use of frac_nobio and vegtot in hydrol is that it is different from its use in hydrolc (Choisnel), in which the "soil" fraction does not include frac_nobio. Despite this difference, the water budget calculations are very similar in hydrol_waterbal and hydrolc_waterbal:

• hydrolc_waterbal:

  tot_water_end(ji) = (mean_bqsb(ji) + mean_gqsb(ji))*vegtot(ji) + &
              & watveg(ji) + snow(ji) + sum_snow_nobio(ji)
  tot_flux(ji) =  precip_rain(ji) + precip_snow(ji) + returnflow(ji) + reinfiltration(ji) + irrigation(ji) - &
               & sum_vevapwet(ji) - sum_transpir(ji) - vevapnu(ji) - vevapsno(ji) - vevapflo(ji) + &
               & floodout(ji)- run_off_tot(ji) - drainage(ji)
  

• hydrol_waterbal:

  tot_water_end(ji) = humtot(ji)*vegtot(ji) + watveg + &
              & snow(ji) + SUM(snow_nobio(ji,:))
  tot_flux(ji) =  precip_rain(ji) + precip_snow(ji) + irrigation (ji) - &
              & SUM(vevapwet(ji,:)) - SUM(transpir(ji,:)) - vevapnu(ji) - vevapsno(ji) - vevapflo(ji) + &
              & floodout(ji) - runoff(ji) - drainage(ji) + returnflow(ji) + reinfiltration(ji)
  

• which was the model for the new total water budget residu (twbr) diagnostic:

  twbr(ji) = (vegtot(ji)*delsoilmoist(ji) + delintercept(ji) + delswe(ji)) &
              - ( precip_rain(ji) + precip_snow(ji) + irrigation(ji) + floodout(ji) &
                 + returnflow(ji) + reinfiltration(ji) ) &
              + ( runoff(ji) + drainage(ji) + SUM(vevapwet(ji,:)) &
                  + SUM(transpir(ji,:)) + vevapnu(ji) + vevapsno(ji) + vevapflo(ji) ) 
  

thermosoil

thermosoil_coef : frac_nobio is used in the computation of the effective soil heat capacity and heat flux by contributing soilcap_nosnow and soilflx_nosnow over its area.

Is this correct ? : The frac_nobio is today only ice and should thus be covered by snow or material of very similar properties. Thus frac_nobio should contribute to the effective soil heat capacity and heat flux snowcap and snowflux. This is directly related to the discussion started by Sylvie Charbit.

thermosoil_profile : frac_nobio is used to compute the effective surface temperature by combining the snow temperature (bottom of snow pack) an the surface temperature computed by enerbil.

explicitsnow

Somebody else should fill this section '''