The farms I've been on (my dad's family are farmers in Iowa) had "storm cellars" as well as basements. The storm cellars are external to the house and usually built into the side of a hill, digging down slightly (about 1/2 story or less). They were wired with electricity and used mostly for storing canned fruits & veggies.
Wiki on storm cellars
My local extention office talks about storm cellars & rooms
Wiki on storm cellars
My local extention office talks about storm cellars & rooms