Changes between Version 91 and Version 92 of Documentation/TrunkFunctionality4


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Timestamp:
03/31/21 17:27:14 (7 months ago)
Author:
luyssaert
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  • Documentation/TrunkFunctionality4

    v91 v92  
    410410 
    411411=== Root profile === 
    412 Describes r7135. Root_profile can and is calculated in the absence of vegetation. Having a root profile even in the absence of the PFT is convenient for when land cover changes happen. The downside is that the history files become unintuitive. To have the best of both worlds we calculate it for every pixel but will do some cleaning before writing the history files which is done in hydrol_main. 
    413  
    414 There are two different ways of looking at the root profile. It could reflect root structure or root function. When thinking at root structure the profile should be relatively constant a logic time integrator to set this constancy would be longevity_root. Root structure is probably how most of us think about roots (i.e. digging a whole and observing where the roots are). In ORCHIDEE root structure is used in the calculation of k_lab which is water infiltration along roots (accounted for in hydrol.f90) and the input of soil carbon and nitrogen at depth due to the turnover of roots which is accounted for stomate_soil_carbon_discretization.f90. 
    415      
    416 When thinking about root function it is not so important where the roots are located it is more important at which depth the roots will be active. The soil function approach is used in the dynamic root profile where the plants can take most of the soil water from the layers where the soil water happens to be. This way of looking at the roots is similar to how we look at the canopy where we have a lot of leaves at places in the canopy where little light can penetrate and where large part of the photosynthesis taken care of by the leaves in the top layers of the canopy. 
    417  
    418 The exponentially decreasing root mass with depth as used for the static root_profile is based on root mass observations and therefore reflects a structural approach. ORCHIDEE uses the same root profile to calculate plant water uptake, infiltration and som inputs. Hence, root function and root  structure are considered the same. The dynamic root profile follows a functional approach based on soil water. An alternative functional approach would be based on nutrient availability as that is another function of the roots. ORCHIDEE uses the same root profile to calculate plant water uptake, infiltration and som inputs. Root function and root structure are also consided the same when using a dynamic root profile. Ideally the code could use a different root profile depending on what we want to use it for.  
     412Describes r713X. There are two different ways of looking at a root profile in the code. It could reflect "structure" or "function". Root structure is probably how most of us think about roots (i.e. digging a whole and observing where the roots are). When thinking at root structure the profile should be relatively constant over time. (A logic time integrator to determine this constancy is longevity_root as the profile cannot grow faster then the roots grow and die -> in ORCHIDEE we simply fixed it over time).   
     413 
     414In ORCHIDEE root structure is used in the calculation of k_lab which is water infiltration along roots (accounted for in hydrol.f90) and the input of soil carbon and nitrogen at depth due to the turnover of roots which is accounted for stomate_soil_carbon_discretization.f90. Furthermore, it is used to calculate the root temperature in stomate_resp.f90. 
     415 
     416When thinking about root function it is not so important where the roots are located but it is more important at which depth the roots will be active. The function approach is used in the dynamic root profile where the plants can take most of the soil water from the layers where the soil water happens to be (feature added by D.Zhu in r4363. I'm not sure which versions this is in but we have it in the 4.x). This way of looking at the roots is similar to how we look at the canopy where we have a lot of leaves at places in the canopy where little light can penetrate and where a large part of the photosynthesis is taken care of by the leaves in the top layers of the canopy. 
     417 
     418The exponentially decreasing root mass with depth which is the default in ORCHIDEE, is based on root mass observations and, therefore, reflects a structural approach. ORCHIDEE uses the same root profile to calculate plant water uptake, infiltration and som inputs. Hence, root function and root structure are considered to be the same.  
     419 
     420The dynamic root profile in ORCHIDEE follows a functional approach based on soil water availability. This seems a fair approach. Plants probably have way more roots than they need exactly to be able to quickly adjust to changes in the soil moisture environment (likewise they have way too many leaves to adjust to the fact that the Earth is rotating and leaves are continuously moving from the wind). If we pass this functional root profile (which is hyper dynamic as it may change every 30 minutes) to the rest of the code, we would introduce scientific inconsistencies in the calculation of infiltration, temperature and som_input. Note: yet another functional approach could be based on nutrient availability as that is another function of the roots.  
     421 
     422Ideally the code should thus use a different root profile depending on what we want to use it for.   
     423 
     424Root_profiles can and is calculated in the absence of vegetation. Having a root profile even in the absence of the PFT is convenient for when land cover changes happen. The downside is that the history files become unintuitive. To have the best of both worlds we calculate it for every pixel but will do some cleaning before writing the history files which is done in hydrol_main. 
    419425 
    420426The approach that has been used in previous versions of the trunk describes the root profile as a truncated exponentially decreasing function of depth. The function is truncated at a prescribed depth ('''maxdepth'''). The shape of the root profile is prescribed by the pft-dependent parameter '''humcste'''. The nodes and interfaces of the soil layers follow the scheme proposed by De Rosnay (PhD thesis). In r4363 a second option was added and a dynamic root profile can be calculated by setting the flag '''ok_dynroot''' to y. The dynamic root profile optimizes soil moisture usage and was modified from Dan Zhu's initial implementation to account for soil layer depth. The root profile that is now calculated in hydrol.f90 is passed to the other subroutines that make use of it.