Opened 2 years ago

Closed 2 years ago

Last modified 2 years ago

#494 closed defect (fixed)

different vpd used to calculate photosynthesis and transpiration

Reported by: vyin Owned by: somebody
Priority: major Milestone:
Component: Physical processes Version: trunc
Keywords: Cc:


The saturated humidity in VPD in diffuco.f90 is calculated by air temperature. It is used to simulate photosynthesis.

But in enerbil.f90, the calculation of transpir uses (qsol_sat_new - qair)

This problem exists in both trunc and MICT.

Change History (3)

comment:1 Changed 2 years ago by aducharne

  • Resolution set to fixed
  • Status changed from new to closed

These differences are normal:

  • in diffuco, you calculate the stress factor exerted by air dryness onto transpiration and photosynthesis, and this stress depends on VPD = qsat(tair) - qair ; eventually, this stress is combined with other stresses into vbeta3
  • in enerbil, you calculate tranpiration, and it dpends on two factors: the stress factor vbeta3 which comes to reduce the potential evaporation; the latter depends on the GRADIENT of q between the surface and the overlying atmopshere = qsat(tsol) - qair


comment:2 Changed 2 years ago by dgoll

I am not quite sure I get your point Agnes. The VPD in the calculation of CO2 fixation (in diffuco) is a different one than the one used in the calculation of transpiration (in enerbil). I would expect that transpiration and photosynthesis 'see' the same VPD.

The point of inconsistency is independent of the choice of the 'correct' VPD. Is there a rationale of having two different VPDs affecting processes which are tightly coupled (via stomates)?

Last edited 2 years ago by dgoll (previous) (diff)

comment:3 Changed 2 years ago by aducharne

Dear Daniel,
my point is that in diffuco, you need the VPD, and in enerbil, you need the vertical gradient of q, not the VPD.

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