why the EFLX_LH_TOT do not equal to Qsoil +Qvege+QVEGT

[xiaoxiaokuishu]

Hi, all

I calculated the

gap=ET/28.36-(qsoil+qve+qvt)*24*60*60 (unit: mm/d).

But I have find most of the value of gap larger than 0 in vegetation regions.

So, which method is accurate to get the ET from CLM, use the ET/28.36 or (qsoil+qve+qvt) ?


Best
Ru

 

[James King]

Hi Ru,

QFLX_EVAP_TOT = QSOIL + QVEGT + QVEGE, i.e. the total evapotranspiration is the sum of the evaporation from the ground, canopy transpiration, and canopy evaporation (in units mm/s). EFLX_LH_TOT is latent heat flux (in units W/m^2). So it may depend on whether you need actual evapotranspiration or latent heat flux (if I have understood the question correctly!)

James

 

[xiaoxiaokuishu]

Hi Ru,

QFLX_EVAP_TOT = QSOIL + QVEGT + QVEGE, i.e. the total evapotranspiration is the sum of the evaporation from the ground, canopy transpiration, and canopy evaporation (in units mm/s). EFLX_LH_TOT is latent heat flux (in units W/m^2). So it may depend on whether you need actual evapotranspiration or latent heat flux (if I have understood the question correctly!)

James

Hi, James,

Thanks for the reply! I need the actual ET, so QSOIL + QVEGT + QVEGE should be actual ET,
but I can also get ET from EFLX_LH_TOT (EFLX_LH_TOT/28.36), I just confused why the calculated

(EFLX_LH_TOT/28.36) do not equal to QSOIL + QVEGT + QVEGE,

for my result,EFLX_LH_TOT/28.36 is larger than QSOIL + QVEGT + QVEGE especially in vegetation regions.


Best
Ru

 

[slevis]

Hi Ru,
I think you should be able to answer this by looking at the calculation of EFLX_LH_TOT in the code (the same equations may also be in the clm technical note, so you could look there first). I would hypothesize that the model does not hardwire the 28.36 conversion the way that you show here. Is 28.36 really a fixed conversion or does it depend on variables like temperature, for example?

 

[xiaoxiaokuishu]

Hi Ru,
I think you should be able to answer this by looking at the calculation of EFLX_LH_TOT in the code (the same equations may also be in the clm technical note, so you could look there first). I would hypothesize that the model does not hardwire the 28.36 conversion the way that you show here. Is 28.36 really a fixed conversion or does it depend on variables like temperature, for example?

Hi, Slevis,
28.36 is a commanly used coversion factor change latent heat to ET (mm), but I am not sure how it come from. I just read it from many papers.

 

[oleson]

The model uses the latent heat of vaporization (2.501 X 10^6 J/kg) to convert between latent heat in W/m2 and evapotranspiration (kg m-2 s-1). But there are other processes such as sublimation of ice/snow that makes a simple conversion not possible.