activate Evapotranspiration as an output in WRF

NoahMP outputs transpiration and evaporation. However, one needs to fully understand the physics behind these variables before combining them to obtain Evapotranspiration. Below are relevant variables:

state real ecanxy ij - 1 - i02rhd=(interp_mask_field:lu_index,iswater)u=(copy_fcnm) "ecan" "evaporation of intercepted water" "mm/s"


state real edirxy ij - 1 - i02rhd=(interp_mask_field:lu_index,iswater)u=(copy_fcnm) "edir" "ground surface evaporation rate" "mm/s"


state real evcxy ij - 1 - i02rhd=(interp_mask_field:lu_index,iswater)u=(copy_fcnm) "evc" "canopy evaporation" "W/m2"


state real qevacxy ij - 1 - i02d=(interp_mask_land_field:lu_index)u=(copy_fcnm) "qevac" "canopy evaporation rate" "mm/


state real etranxy ij - 1 - i02rhd=(interp_mask_field:lu_index,iswater)u=(copy_fcnm) "etran" "transpiration rate" "mm/s"


state real trxy ij - 1 - i02rhd=(interp_mask_field:lu_index,iswater)u=(copy_fcnm) "tr" "transpiration" "W/m2"

Please see details in registry.noahmp and related codes.
 
Ming Chen said:
NoahMP outputs transpiration and evaporation. However, one needs to fully understand the physics behind these variables before combining them to obtain Evapotranspiration. Below are relevant variables:

state real ecanxy ij - 1 - i02rhd=(interp_mask_field:lu_index,iswater)u=(copy_fcnm) "ecan" "evaporation of intercepted water" "mm/s"


state real edirxy ij - 1 - i02rhd=(interp_mask_field:lu_index,iswater)u=(copy_fcnm) "edir" "ground surface evaporation rate" "mm/s"


state real evcxy ij - 1 - i02rhd=(interp_mask_field:lu_index,iswater)u=(copy_fcnm) "evc" "canopy evaporation" "W/m2"


state real qevacxy ij - 1 - i02d=(interp_mask_land_field:lu_index)u=(copy_fcnm) "qevac" "canopy evaporation rate" "mm/


state real etranxy ij - 1 - i02rhd=(interp_mask_field:lu_index,iswater)u=(copy_fcnm) "etran" "transpiration rate" "mm/s"


state real trxy ij - 1 - i02rhd=(interp_mask_field:lu_index,iswater)u=(copy_fcnm) "tr" "transpiration" "W/m2"

Please see details in registry.noahmp and related codes.
Click to expand...
Hi, Ming

the Evapotranspiration = ecan + edir +etran, right?
 
Ming Chen said:
Yes you are right.
Click to expand...
Hi,

Sorry, I have another question. I didn't find the evaporation items for water body and snow in wrfout* files.
If I want to calculate the total evapotranspiration of a specified watershed, which contains water bodies. How I calculate the total evapotranspiration? I think Evapotranspiration = Ecan + Edir +Etran may be incorrect, Evapotranspiration = Ecan + Edir +Etran+Ewater + Esnow should be right.

Or should I convert the latent heat flux into evapotranspiration using the formula: ETdaily (mm/d)=LH/λ×86400?
 
WRF LSM (Noah, NoahMP, RUC, etc.) only calculates evapotranspiration over land points. Evaporation at water points can be derived from latent heat flux. The basic relation between latent heat flux (LH) and evaporation rate is: EVAP = LH/Lv, where:
  • EVAP = evaporation rate (kg m−2−2 s−1−1)
  • LH = latent heat flux (W m−2−2 = J s−1−1 m−2−2)
  • Lv = latent heat of vaporization (J kg−1−1)
 
Ming Chen said:
WRF LSM (Noah, NoahMP, RUC, etc.) only calculates evapotranspiration over land points. Evaporation at water points can be derived from latent heat flux. The basic relation between latent heat flux (LH) and evaporation rate is: EVAP = LH/Lv, where:
  • EVAP = evaporation rate (kg m−2−2 s−1−1)
  • LH = latent heat flux (W m−2−2 = J s−1−1 m−2−2)
  • Lv = latent heat of vaporization (J kg−1−1)
Click to expand...
I still have some doubts.
In your formula, EVAP = LH/Lv. I guess EVAP should be refer to the evaporation (only including water points)?

However, as i understand it, I think EVAP should be the total evapotranspiration (including land and water points), because LH is the area-weighted average latent heat flux of land and water patches within each grid cell. I am not sure if it is correct.

Looking forward to your reply
 
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