How to interpret the negative (actual) evapotranspiration values?
Negative values for the ET, both potential and actual, usually refer to condensation.
See also &quot;ERA5 mean evaporation rates data - Why is that negative?&quot;
Regarding the ability of the physically-based hydrological models to handle condensation, I'd say that it's difficult to give you a general answer: it will depend on the specific math behind the model, but my general guess would be that they do.
Even a simple Bucket Model, would integrate condensation in the water balance equation. While a more sophisticate Earth System Model would probably process it in the soil moisture and/or canopy component, in order to better represent these dynamics in the water-energy balance of the specific system. See for instance Longo et al 2019