| 23 | | 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 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. |
| | 23 | 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 trunk 4, 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 trunk 4 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. |
| 29 | | * 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 |
| 30 | | * Because we still use the 13 default MTCs we can use the default maps. Let the model know how many MTCs it should find on the maps: NVMAP=13 |
| | 29 | * Assume we want to use four age classes for all forests. We will end-up with 37 PFTs: one each for bare soil, three C3 grasses, C4 grass, C3 crop and C4 crop and 4 times 8 for the 8 forest PFTs. Thus NVM = 39 |
| | 30 | * Because we still use the 13 default MTCs we can use the default maps. Let the model know how many MTCs it should find on the maps: NVMAP=15 |
| 75 | | 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 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. |
| | 75 | 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). 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 trunk 4 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 trunk 4 cannot revert to previous approaches for calculating albedo. |
| 81 | | === Albedo (background) (CHECK) === |
| 82 | | If covered by snow, the background albedo is calculated by the snow module and accounts for snow age and snow density (needs to be checked – last time snow did not account for NIR). If not covered by snow, the background albedo is not simulated but prescribed by the parameters '''bgrd_ref_vis''' and '''bgrd_ref_nir'''. If the background is partly covered by snow, the snow albedo and the background albedo are merged, which allows snow to settle under the canopy, reflecting In deciduous forest, grasslands and croplands, the background albedo is known to be strongly affected by the phenology and senescence of the understory vegetation. ORCHIDEE-CN-CAN has two options to prescribe the background albedo: |
| 83 | | * The background albedo is prescribed per PFT but is constant throughout the year. This is the option that has been used in ORCHIDEE-CAN and is the option that has been validated over Europe. Set '''alb_bg_modis''' = n. |
| 84 | | * The background albedo is constant across PFTs. This option reads background maps. Given that those maps are based on the JRC TIP product, they should be compatible with the new albedo scheme. This option, however, has not been validated yet. Set '''alb_bg_modis''' = y. |
| | 81 | === Albedo (background) (r6614) === |
| | 82 | If covered by snow, the background albedo is calculated in the VIS and NIR wavelengths by the snow module and accounts for snow age and snow density. If not covered by snow, the background albedo is not simulated but prescribed by the parameters '''bgd_reflectance(:,ivis)''' and '''bgd_reflectance(:,ivis)'''. If the background is partly covered by snow, the snow albedo and the background albedo are merged, which allows snow to settle under the canopy, reflecting In deciduous forest, grasslands and croplands, the background albedo is known to be strongly affected by the phenology and senescence of the understory vegetation. ORCHIDEE trunk 4 has two options to prescribe the background albedo: |
| | 83 | * The background albedo is prescribed per PFT but is constant throughout the year. This option has been evaluated over Europe. Set '''alb_bg_modis''' = n. |
| | 84 | * The background albedo is constant across PFTs. This option reads background maps. Given that those maps are based on the JRC TIP product, they should be compatible with the new albedo scheme. This option, however, has not been evaluated yet. Set '''alb_bg_modis''' = y. |
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