Brief description of the modifications done into LPJ module

The change in units in STOMATE (i.e definition of variables in total m² not m²*veget_max) induced several modifications in the vegetation dynamics that was not taken into account. Also an update of dynamics from recents version of LPJ have been taken into account as well as some errors compared to the initial version. These work was done by Z. Saehle. Main bug corrected was:

• biomass per individual was not divided by surface of the pfts but it should be as individual is related the pft surface
• likewise total biomass was not recalculated to take into account for the change in veget_max
• calculation of dynamics was incorrect (it was the main reason for including a constant mortality).
• to be able to separate between C3 and C4 grass, the establishment rate is now function of long term npp
• agricultural area was not taken into account for calculation of surface covered by natural vegetation and then for competition
• annual fpc coverage was based on mean LAI that is not fair for deciduous compared to evergreen. Now it is based on max LAI
• Calculation of woodmass_ind was removed from lpj_crown as it cannot be calculated correctly after introduction of a PFT

Another change (not directly impacting the vegetation dynamics but more realistic and that would allow to shift for static to dynamic mode correctly) is that the number of individual (IND) and individual crown (CN_IND) is now calculated dynamically even in static mode. Some bug correctly in the version of Sönke was also corrected.

Evaluation of this new version

For all the simulations that have been tested, we use a simulation performed with V1.6 and provided by Nathalie De Noblet. They all run 200 years using a climatology from CRU (monthly data) provided by Nathalie as well. We first ensure that we were capable to re-do the simulation performed by Nathalie. Below is the PFT distribution of natural vegetation (one PFT per column) for the simulation performed by Nathalie (upper panel), and our simulation (middle panel) and the difference between the two (lower panel).

We then ran a simulation with the tag 1.9.5.1, to check how ORCHIDEE was performing before changes. Here below is a comparison with the simulation provided by Nathalie. The main changes are :

• The high latitudes are defined as 100% noBio fraction.
• Increase of the fraction of Bare Soil in Central Asia at the expense of Grass PFT.
• Extension of the Tropical PFT zone in Africa at the expense of C3 and C4 grass PFT.
• Extension of the zone occupied by 'Temperate broad-leaved summergreen' (but with low fraction).
• Change in the fractions occupied by Boreal PFT.

Last, we evaluate how performs the version of ORCHIDEE updated for LPJ module.

Other simulations have been performed by Nicolas Viovy using CRU-NCEP data. When compared with simulations based on CRU, they give similar results. Here below, is a comparison for the version 1.9.5.2_debug2:

About the PFT "boreal needleleaf evergreen forests" that disappeared in the tag version 1.9.5.2, it seems that it has been introduced when the flag const_mortality has been desactivated. Here below, a comparison between version 1.9.5.1_debug2 and 1.9.5.1_debug2_morta: