= Evolution of the functionality of the ORCHIDEE model =

Table 1. Concise description of processes (in alphabetical order) simulated in subsequent model versions
|| CHECKED? || '''Process''' || '''ORCHIDEE Krinner et al. 2005''' || '''ORCHIDEE v2.1 Peylin et al. ''' || '''ORCHIDEE v3.0 Vuichard et al 2019''' || '''ORCHIDEE 4.0 Naudts et al. 2015''' ||
|| Yes || Age classes || Not available || Not available || Not available || Age classes were introduced to better handle heterogeneity at the landscape level. Age classes are independent of the number of diameter classes. Using age classes adds a lot of details to both the biophysics and the biogeochemistry following natural disturbances, forest management and land cover change. Age classes are defined as separate PFTs that form an age group ([https://forge.ipsl.jussieu.fr/orchidee/wiki/Documentation/TrunkFunctionality4#Ageclassesr6614 More]) ||
|| No || Albedo (background) || || || || ||
|| No || Albedo (snow) || || || || ||
|| Yes || Albedo (vegetation)  || For each PFT the total albedo for the grid square is computed as a weighted average of the vegetation albedo and the background albedo. The background albedo is composed by a snow and soil albedo. The soil albedo depends on the soil properties. || Rather than using soil properties, ORCHIDEE v2.1 uses spatially explicit observation-derived estimates for its background albedo in the absence of snow. || No changes from the previous version. || ORCHIDEE trunk 4 makes use of a two stream radiative transfer scheme through the canopy, extended to multiple canopy levels ([https://doi.org/10.5194/gmd-2016-280 More]). The scheme is based on Pinty et al 2006. This approach accounts not only for the leaf mass but also for the vertical and horizontal distribution of the leaf mass (= canopy structure), calculating an effective LAI based on the solar angle. Light from collimated (black sky) and diffuse (white sky) sources are used, and both are weighted equally as information about this partitioning is not yet available in forcing data ([https://forge.ipsl.jussieu.fr/orchidee/wiki/Documentation/TrunkFunctionality4#Albedor6614 More]). ||
|| No || Biogeography ||  Describe what was done in Krinner et al 2005 || Zhu et al 2.1or MICT? || No changes || Not yet available in this version ||
|| No || Biological volatile emissions || Not applicable || Why was it added? What is added? || No changes || No changes ||
|| No || Carbon allocation || Carbon is allocated to the plant following resource limitations (Friedlingstein et al 1999). Plants allocate carbon to their different tissues in response to external limitations of water, light and nitrogen availability. When the ratios of these limitations are out of bounds, prescribed allocation factors are used. || No changes || || No changes ||
|| No || Energy budget || The coupled energy balance scheme, and its exchange with the atmosphere, is based on that of Dufresne and Ghattas (2009). The surface is described as a single layer that includes both the soil surface and any vegetation. The energy budget is solved with an implicit numerical scheme that couples the lower atmosphere to the surface, in order to increase numerical stability. || No changes || No changes || No changes ||
|| No || Grass and crop harvest || Describe what was done in Krinner et al 2005. || No changes || No changes || Half of the daily grass turnover is moved in the short lived product pool. At the time crops are harvested all of the harvest which is half of the biomass is moved into the short lived product pool. ||
|| No || Growth respiration || A prescribed fraction of 28 % of the photosynthates allocated to growth is used in growth respiration (McCree, 1974). The remaining assimilates are distributed among the various plant organs using the allocation scheme || No || No changes || No changes || No changes ||
|| No || Land cover change || Not applicable || Piao et al 2205? || No changes || No changes ||
|| No || Maintenance respiration || Maintenance respiration contributes together with growth respiration to the autotrophic respiration. Maintenance respiration occurs in living plant compartments and is a function of temperature, biomass and, the prescribed carbon/nitrogen ratio of each tissue (Ruimy et al., 1996)|| No change || Describe the changes || No changes ||
|| No || Mortality and turnover || All biomass pools have a turnover time. Living biomass except the sapwood is transferred to the litter pool, litter is decomposed or transferred to the soil pool. Sapwood is converted into heartwood. || No changes || No changes || Woody biomass no longer has a turnover pool. Trees are killed self-thinning or harvest. Depending on the cause of the mortality the carbon is entirely moved into the litter pool (for self-thinning) or mainly moved into the harvest pool with the remainder contributing to the litter pool (for harvests). || 
|| No || Phenology || At the end of each day, the model checks whether the conditions for leaf onset are satisfied. The PFT-specific conditions are based on long and short term warmth and/or moisture conditions (Botta et al., 2000). || No changes || No changes || No changes ||
|| No || Photosynthesis || C3 and C4 photosynthesis is calculated following Farquhar et al. (1980) and Collatz et al. (1992), respectively. A semi-analytical approach is used to solve the set of equations for photosynthesis, stomatal conductivity  and internal CO2 concentration in the leaf at the PFT level. || The semi-analytical solution was replaced by an analytical solution (Yin and Streuk 2009). The Vcmax parameter was redefined. The analytical solution is faster than the semi-analytical solution and by redefining vcmax, large observational database could be used to parameterize the model || No changes || LAI layering ||
|| No || Product use || Not applicable || Piao et al 2005 || Previously product pools were only accounted when land cover change was activated. In an experiment where land cover change was followed by a treatment with land cover change the product pool was frozen during the second part of the experiment. This has been changed such that the decomposition of the product pool is calculated irrespective of whether land cover change is activated or not. || Previous version assign fixed values of the wood harvest to the short, medium and long-lived product pools. The model now has two approaches: (1) the previous approach with fixed ratios between the pools and a dynamic approach in which wood below a certain diameter goes into the short lived pool and wood above a certain diameter is distributed over the medium and long-lived product pool according to fixed values. The definition (=longevity) of the short, medium and long-lived is no longer fixed as before but became a user setting ||
|| No || Roughness || Describe how it is calculated in Krinner et al 2005 || Roughness is observed to be different for heat and momentum. Also the roughness is driven by the leaf area. The formulation of Shu et al.is now used to account for the leaf area when calculating a separate roughness length for heat and momentum. || No changes || No changes ||
|| No || Routing || Not applicable || How is it calculated in ORCHIDEE 2.1. \citep{NgoDuc2007}? || No changes || No changes ||
|| No || Senescence || Describe how senescence is calculated in Krinner et al 2005. || No changes || No changes || No changes ||
|| No || Snow temperature and dynamics || Describe snow energy budget in Krinner et al 2005 || How is it calculated now? See Tao || No changes || No changes ||
|| No || Soil hydrology || Describe bucket model. Calculated for X soil columns. || Vertical water flow in the soil is based on the Fokker-Planck equation that resolves water diffusion in non-saturated conditions from the Richards equation (Richards, 1931). The 4 m soil column consists of eleven moisture layers with an exponentially increasing depth (D'Orgeval et al., 2008). Bare soil, short vegetation, and tall vegetation each have their own water column. || No changes || No changes ||
|| No || Soil and litter carbon and heterotrophic respiration || Following Parton et al. (1988), prescribed fractions of the different plant components go to the metabolic and structural litter pools following senescence, turnover or mortality. The decay of metabolic and structural litter is controlled by temperature and soil or litter humidity. For structural litter, its lignin content also influences the decay rate. || If there is insufficient N available to support the decomposition of the litter and soil carbon, heterotrophic respiration will be limited by the Nitrogen availability  || No changes ||
|| No || Soil temperature || The soil temperature is computed according to the Fourier equation using a finite difference implicit scheme with seven numerical nodes unevenly distributed between 0 and 5.5 m (Hourdin, 1992). ? How many soil temperature columns did we have ? || The differences in the vertical discretisation between the soil hydrology and soil temperature resulted in difficulties to conserve energy. The soil hydrology and temperature are calculated on a single vertical discretisation. A separate soil temperature is calculated for the bare soil, short vegetation, and tall vegetation. || No changes || No changes ||
|| No || Vegetation distribution || Krinner et al 2005 describes global vegetation by 13 meta-classes (MTCs) with a specific parameter set (one for bare soil, eight for forests, two for grasslands and two for crop-lands) || The implementation of the MTC was generalized such that more than one PFT can be used to represent an MTC. ORCHIDEE 2.1 uses 13 MTCs to define 15 PFTs. || No changes || No changes || 
|| No || Wood harvest || Not applicable || Wood harvest following LUHv2 maps. LUHv2 prescribes the amount of biomass to be harvested. Wood harvest is accounted for at the PFT level. || No changes || LUHv2 maps are used to decide whether the forests in a pixels are managed or not. If the forest is managed, ORCHIDEE calculates the harvested biomass following an RDI approach. ||