Too frequent zero LAI in time series

[luyssaert]

In r6904 the large scale LAI is starting to look OK but when zooming in on the time series this version still has many more years with a zero LAI compared to ORCHIDEE 3 and Tag 2.1. This may be caused by:

• Problems with phenology (only if phenology is in part driven by soil moisture). Possible for PFT3, 10, 11, 12, 13, 14 and 15.
• Problems with Rm. If Rm > GPP during the senescence phase the reserves and labile C pools will be empty by the end of the year resulting in zero LAI the next year.
• PFTs 10, 11, 12, 13, 14 and 15 hardly grow. The grasslands have a rather high within-season turnover which may explain their limited growth but this is suspicious for the crop PFTs and finding its cause could help to solve this ticket.

[luyssaert]

Problems with phenology (only if phenology is in part driven by soil moisture). Possible for PFT3, 10, 11, 12, 13, 14 and 15.

• This happened 5 to 10% of the years in PFT 10, 12 and 13 between 1910 and 1930 over the Americas. It rarely (or never) happened for the other PFTs with pheno model = moigdd. A fail safe has been implemented in r6918. This will reduce the many zero LAI values but it is not the main cause of the problem.

PFTs 10, 11, 12, 13, 14 and 15 hardly grow. The grasslands have a rather high within-season turnover which may explain their limited growth but this is suspicious for the crop PFTs and finding its cause could help to solve this ticket.

• In the temperate zone PFT 12 and 13 suffer from N-limitations when using pre-industrial configuration such as the spinup with r6931. When impose_cn = y these PFTs grow very well. A global simulation including FG2 should enable us investigating whether the transient behavior of the model (in terms of increasing N-availability) is acceptable.
• In r6931, the phenology of the grasslands is still too poor to further look into the issue. Preliminary results show that more N-availability (impose_cn = y) can make the grasslands behave as evergreen PFTs (most likely because better growth and turnover keeps the mean leaf age low).
• Some of these issues seem to have been fixed by r7004 and r7012.

Problems with Rm. If Rm > GPP during the senescence phase the reserves and labile C pools will be empty by the end of the year resulting in zero LAI the next year.

• Code changes were made in r6947 and r7012.

In r7012 grasslands in arid and semiarid regions are subject to frequent dying, which is problematic. This causes further problem of frequent false uptake of GPP simply by prescribing new sapling biomass for grassland. This potential problem needs to be fixed. It may in part be related to simulating a wrong starting date and or a too short growing season (which does not leave enough time to restore the reserves).