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.

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 ?

diffuco

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

thermosoil