I've tried searching the forums for an answer to this question but I've seen different responses:

Anyone know what exactly the penalties are for losing the resource required to maintain a unit? Is it just a combat penalty or is there an upkeep increase too?

What about a building?

There is a -50% combat penalty for all units that require a particular resource if you don't have enough of that resource.
No impact on upkeep AFAIK.

I'm not sure if there's any penalty for resource-requiring buildings. Would be good to see confirmed.

I'd like to know for buildings too (mostly for modding purposes). Does anyone know if benefits disappear for already existing buildings? If so, will they only disappear for one instance of the building (assuming you are at -1 for that resource)?