Changes between Version 240 and Version 241 of DevelopmentActivities/ORCHIDEE-DOFOCO


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Timestamp:
2020-01-22T16:24:39+01:00 (4 years ago)
Author:
luyssaert
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  • DevelopmentActivities/ORCHIDEE-DOFOCO

    v240 v241  
    7474== Functionalities (alphabetical order) == 
    7575 
    76 === Age classes === 
    77 Age classes were introduced to better handle heterogeneity at the landscape level. The feature allows us to distinguish between different successional stages of the same PFT (e.g., a newly grown forest vs. a mature forest). 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. If half of a grassland is afforested with a PFT that already exists in the pixel, previous versions of ORCHIDEE will combine this newly forest land and the existing forest in a single PFT. This will result in, for example, a low albedo, a high roughness, and other properties.  When age classes are used, the newly afforested and the existing forest will end up in separate PFTs. One will have a high albedo, the other a low albedo, and other properties may differ significantly as well. In CAN with age classes, PFTs are only merged if the youngest age class for a PFT already has biomass when an older age class is killed. 
    78  
    79 Age classes are defined as separate PFTs.  Different age classes of the same PFT could therefore be, in principle, run with different parameters. This option has not been tested yet because it is expected to result in discontinuities when the biomass is moved from one age class to another. The number of age classes is fixed for the whole simulation, but for each PFT it can be decided whether age classes are used or not. In other words, if the user chooses four age classes for the simulation, each PFT can have either 1 or 4 age classes.  This adds a lot of flexibility to the model. ORCHIDEE-CAN, for example, has been run with 64 PFTs, using age classes for European forest and using no age classes for all forests outside the domain of interest. Setting-up a simulation with age classes will require some thinking when creating the run.def. A Python-script was written to create this kind of run.def. Increasing the number of PFTs has important consequences for the speed of the model and the memory use, although ORCHIDEE-CAN does make extensive use of "CYCLE" statements to avoid calculations where no biomass is present. Because a single run can contain PFTs with and PFTs without age classes, processing of the simulation output needs to account for the relationship between PFTs of the same species but a different age class. 
    80  
    81 It does not make sense to use age classes for runs ignoring land cover change.  Age classes can be used for site level simulations that involve land cover change.  Only use age classes if you really need them (e.g., land cover change), as not using age classes will make post processing of the simulation results considerably easier. 
    82  
    83 The number of age classes is defined by the parameter '''NAGEC'''. Setting this parameter to 1 is a good start unless you have a special interest in using age classes. When NAGEC is set to more than 1, '''PFT_TO_MTC'''', '''AGEC_GROUP''' and '''PFT_NAME''' will all need to be carefully defined. See the attached run.def for a functional example. See below for some principles:  
     76=== Age classes (as in r6470) === 
     77Age classes were introduced to better handle heterogeneity at the landscape level. The feature allows us to distinguish between different successional stages of the same PFT (e.g., a newly grown forest vs. a mature forest). 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. If half of a grassland is afforested with a PFT that already exists in the pixel, previous versions of ORCHIDEE will combine this newly forest land and the existing forest in a single PFT. This will result in, for example, a low albedo, a high roughness, and other properties.  When age classes are used, the newly afforested and the existing forest will end up in separate PFTs. One will have a high albedo, the other a low albedo, and other properties may differ significantly as well. In CAN with age classes, PFTs are only merged if the youngest age class for a PFT already has biomass. 
     78 
     79Age classes are defined as separate PFTs. Different age classes of the same PFT could therefore be, in principle, run with different parameters. This option has not been tested yet because it is expected to result in discontinuities when the biomass is moved from one age class to another. The number of age classes is fixed for the whole simulation, but for each PFT it can be decided whether age classes are used or not. In other words, if the user chooses four age classes for the simulation, each PFT can have either 1 or 4 age classes.  This adds a lot of flexibility to the model. ORCHIDEE-CAN, for example, has been run with 64 PFTs, using age classes for European forest and using no age classes for all forests outside the domain of interest. Setting-up a simulation with age classes will require some thinking when creating the orchidee_pft.def. A Python-script was written to create this kind of run.def and is stored in config/ORCHIDEE_OL/MAKE_RUN_DEF. Increasing the number of PFTs has important consequences for the speed of the model and the memory use, although ORCHIDEE-CAN does make extensive use of "CYCLE" statements to avoid calculations where no biomass is present. Because a single run can contain PFTs with and PFTs without age classes, processing of the simulation output needs to account for the relationship between PFTs of the same species but a different age class. 
     80 
     81It does not make sense to use age classes for runs ignoring land cover change and forest management.  Age classes can be used for site level simulations that involve land cover change.  Only use age classes if you really need them (e.g., land cover change, forest management, other disturbances), as not using age classes will make post processing of the simulation results considerably easier. 
     82 
     83The number of age classes is defined by the parameter '''NAGEC'''. Setting this parameter to 1 is a good start unless you have a special interest in using age classes. When NAGEC is set to more than 1, '''PFT_TO_MTC'''', '''AGEC_GROUP''' and '''PFT_NAME''' will all need to be carefully defined. See the different orchidee_pft.defs that come with the standard configurations in config/ORCHIDEE_OL for functional examples. See below for some principles:  
    8484* NAGEC = 4 
    8585* Assume we want to use four age classes for all forests. We will end-up with 37 PFTs: one each for bare soil, C3 grass, C4 grass, C3 crop and C4 crop and 4 times 8 for the 8 forest PFTs. Thus NVM = 37 
    … …  
    128128}}} 
    129129 
    130 === Albedo (general) === 
    131 ORCHIDEE-CN-CAN 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). 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 avaialble in forcing data.  In ORCHIDEE-CN-CAN the same scheme is used to simulate the reflected, transmitted and absorbed light, of which the absorbed light as a function of canopy level is passed to the photosynthesis routines and used in place of the expontential LAI layering found in older versions of the TRUNK (see the section Photosynthesis). This implies that albedo and photosynthesis are now fully consistent as well as the light reaching the forest floor (the latter is used in for example recruitment). ORCHIDEE-CN-CAN cannot revert to previous approaches for calculating albedo. 
     130=== Albedo ((as in r6470) === 
     131ORCHIDEE-CN-CAN 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). 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.  In ORCHIDEE-CN-CAN the same scheme is used to simulate the reflected, transmitted and absorbed light, of which the absorbed light as a function of canopy level is passed to the photosynthesis routines and used in place of the exponential LAI layering found in older versions of the TRUNK (see the section Photosynthesis). This implies that albedo and photosynthesis are now fully consistent as well as the light reaching the forest floor (the latter is used in for example recruitment). ORCHIDEE-CN-CAN cannot revert to previous approaches for calculating albedo. 
    132132  
    133133The radiative transfer through the canopy is controlled by 3 parameters for each wavelength/band: single leaf scattering '''leaf_ssa_xxx''', forward scattering '''leaf_psd_xxx''' and background reflectance '''bgrd_ref_xxx'''. At present, both the visible (VIS) and near-infrared (NIR) spectra have been parameterized. Parameterization is based on running an inverse radiation scheme on the MODIS albedo product while accounting for the different land cover types. The inverted parameters are provided by the JRC as the JRC TIP product. Seasonal variation in the background albedo was observed but small and therefore not accounted for.