Changes between Version 90 and Version 91 of Documentation/TrunkFunctionality4


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Timestamp:
03/31/21 16:42:01 (7 months ago)
Author:
luyssaert
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  • Documentation/TrunkFunctionality4

    v90 v91  
    410410 
    411411=== Root profile === 
    412 Describes r7135. The 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 th epft-dependent parameter '''humcste'''.  
    413  
    414 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 acount for soil layer depth. This flag only affects how roots are calculated in hydrol.f90 but has no impact on how the root profile is calculated in stomate_resp.f90, stomate_litter.f90, stomate_soil_carbon_discretization.f90, hydraulic_architecture.f90 andstomate_windthrow.f90.  
    415  
    416 In r6824 a third approach was added but only affects the calculation of water stress in hydraulic_architecture. This approach is very similar to what has been done in hydrology but the moisture content (kg/kg) is used rather than soil moisture in (m-2/kg) and to enable better testing a second flag was introduced ('''ok_dynroot_ha'''). Note that when ok_dynroot_ha is set to true, the variable e_frac is passed from hydraulic architecture to hydrol and therefore the root profile calculated in hydraulic architecture will be used in hydrol when the transpiration is take out of the different soil layers. Following some tests and additional discussion it is probably worth to clean the code, enhance the consistencies across the modules and reduce the number of variables names (see ticket #715).  
     412Describes 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 
     414There 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     
     416When 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 
     418The 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.  
     419 
     420The 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.  
    417421 
    418422'''Table''' The root profile interacts with the use of hydraulic architecture and soil discretization. Each of these combinations should be checked and tested.