Hi @nic.keller,
Sorry for the really slow follow up! I asked around a bit but didn’t get a ton of feedback from the model developers.
I think some takeaways are that technically you should probably be providing reference ET. Potential ET is similar, but different, and the model wasn’t designed with that in mind. However, initial thought is that it would be ok to use actual ET and set Kc to 1, since it is creating an index of evapotranspiration (not an absolute value that it’s more important to get the actual value correct) that includes vegetation type, and that’s akin to Actual ET.
Perhaps @Perrine, @RafaSchmitt, @chris or others could pitch in?
Doug