I'm pretty sure that most if not all random events will be beneficial, or risky with high end benefit. Even then, the majority of those will probably also be story / added quest related.
Anything horrible detrimental to enjoyment of the game I would simply rule out as an option. Something like a natural disaster I could certainly see, but it would be only a smaller hindrance.
I would enjoy some weather and environmental elements causing for interesting battles, however. Maybe rain or snow could make the fog of war tighter due to lower troop visibility? Maybe a shortcut across a part of land is available because a pond is frozen? That could prove interesting.