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 with vegetation. These fraction can be covered by glaciers, cities lakes or any other surface type where no biological activity (transpiration, assimilation, decomposition, ...) will happen.

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 the frac_nobio is used and with which intention.

general comments

the 2 variables frac_nobio and totfrac_nobio are passed to most subroutines and thus this is redundant information as in principle totfrac_nobio(:) = SUM(frac_nobio(:,jv), jv=1,nnobio) but nowhere is it verified that the this is indeed true.

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

Thus a first step in an effort to better handle the no-bio fraction would be to clean-up the code and only use frac_nobio and deal properly with its second dimension.

slowproc

slowproc_veget : computes the frac_nobio from the vegetation map read by summing all the fractions which are covered by ice, lakes, cities, ...

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.

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 : used 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 (vbeta?, soilflx, soilcap, ...).

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. Il 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.

thermosoil

explicitsnow

Somebody else should fill this section '''