why is qflx_evap_veg > 0 when h2ocan = fwet = 0???

[cory_pettijohn@oregonstate_edu]

The calculation of intercepted canopy water evaporation, 'qflx_evap_veg' in CanopyFluxesMod.F90 (CLM3.5) is confusing me beyond end. The following are true for a particular time step:

h2ocan(p) = 0
fwet = 0
efpot > 0
btran(p) > 0

Given the above, the fraction of pot. evap. from the leaf, rpp, is calculated as:

rpp = rppdry + fwet(p)
...
rpp = min(rpp, (qflx_tran_veg(p)+h2ocan(p)/dtime)/efpot)

As qflx_evap_veg is :

qflx_evap_veg = rpp*efpot

CLM calculates a non-zero, positive qflx_evap_veg flux even though fwet = 0 and h2ocan = 0. What is going on? Why is qflx_evap_veg not:

qflx_evap_veg = efpot*fwet? Or at least rpp = 0 when fwet = 0?

Is this related to a forced method of closing the canopy EB? Am I confusing myself, and qflx_evap_veg is total ET from the vegetation? I have been under the assumption that qflx_evap_veg and qflx_tran_veg are E_v^w and E_v^t, respectively, in Eq. 5.85 from the Oleson et al. (2004) Tech. Description of the CLM...

 

[cory_pettijohn@oregonstate_edu]

okay, now I see from Biogeophysics2Mod.F90 that qflx_evap_veg is total canopy ET, and that qflx_evap_veg - qflx_tran_veg is the intercepted canopy water evap. *whew* it would be helpful in the variable defs in CanopyFluxesMod if instead of 'vegetation evaporation' for 'qflx_evap_veg' it would read 'vegetation evapotranspiration'