# Any way to output potential evapotranspiration (PET) in CLM5?

#### shirleyxyliu@gmail_com

##### New Member
Hi all, I'm just wondering if there is any way to output potential evapotranspiration (PET) in CLM5 with compset I2000Clm50BgcCrop? I already outputted evapotranspiration (ground evaporation + vegetation evaporation + vegetation transpiration), but I do not see how and where CLM calculates their counterparts in 'potential' terms. Thanks!

Shirley

#### oleson

##### CSEG and Liaisons
Staff member
CLM doesn't use the potential evaporation concept, so there aren't any readily available output variables for that. One could maybe find a way to calculate unstressed versions of the evaporation terms by eliminating the stress terms, but probably not easily done.

#### msulis

##### New Member
Hi Keith, I am coming back to the above question. Would "efpot" local variable in PhotosynthesisMod.F90 suitable for this purpose? Thanks in advance for the clarification!

Best,
Mauro

#### oleson

##### CSEG and Liaisons
Staff member
My understanding is that PET is the ET in the absence of soil moisture limitation, so it depends on the particular ET equation and the soil moisture stress equation. One could write an equivalent equation for CLM, but then would have to calculate stomatal conductance in the absence of soil moisture stress.
efpot in CLM is just atmospheric demand.

#### msulis

##### New Member
Thanks Keith, this clarifies my point.

Best wishes,
Mauro

#### dayon

##### Member
My understanding is that PET is the ET in the absence of soil moisture limitation, so it depends on the particular ET equation and the soil moisture stress equation. One could write an equivalent equation for CLM, but then would have to calculate stomatal conductance in the absence of soil moisture stress.
efpot in CLM is just atmospheric demand.
Hi, Oleson, Would you like to explain the difference between the qflx_evap_can (evaporation from leaves and stems) and the qflx_evap_veg (vegetation evaporation)? which of two is interception loss?

#### oleson

##### CSEG and Liaisons
Staff member
Sorry for the slow response, out on vacation.
qflx_evap_can is evaporation from leaves and stems (so, interception loss).
qflx_evap_veg is transpiration plus evaporation from leaves and stems (total evaporation from vegetation).