Hi @kjbagstad, I’m sorry I don’t have any specific recommendations for this case (and it is an interesting one), but I’ll ping a few folks about it. That being said, the LULC_veg parameter determines which AET equation is used for this landcover, so if there is an AET equation that would make the most sense for your sparse vegetation case, perhaps that would drive the decision one way or another? The two equations are labeled 1 and 2 in https://invest-userguide.readthedocs.io/en/latest/reservoirhydropowerproduction.html for your reference.
Hope this helps!
James