Unsaturated percentage as attribute
It would be nice if you could specify the initial value for the saturation degree based on an area. This way you can distinguish between wet areas and dry areas (for example clay and peat versus sand). I imagine you specify these values in the same way as the RAIN_AREAS.
Documentation:
https://support.tygron.com/wiki/Unsaturated_fraction_prequel_(Water_Overlay)