Does it expect actual ET or potential ET?
Yes, I think that Potential Evapotranspiration is the required input. From what I understand Reference Evapotranspiration (ET_0) is Potential Evapotranspiration calculated at a nearby climatic station on a reference surface. ( Full disclosure, pulling from Wikipedia ).
Since our raster is actual ET, we are considering using a Kc value of 1 for all land use categories in the biophysical table. Is that valid?
Hmmm. Good question. The model creates and uses an evapotranspiration index which represents a normalized value of potential evapotranspiration (From the Users Guide - UCM)
I’m not comfortable saying that equation 1 in the Users Guide would actually reflect passing in AET with Kc values of 1…
Hopefully this is somewhat helpful. I’m not the model designer, but can reach out if you’d like more clarity.