An odd discussion came up on a role-playing game forum recently. Some people were speculating about how a mediaeval society would be different if it had wizards, with the spells described in the game rules. One of the spells creates heavy rain - the rules specify 1 inch per hour, over a certain area. Somebody was commenting whether or not this spell would have a big effect on agriculture, and added "unless the crops can't take an inch of rain in an hour, in which case we're looking at this spell all wrong".
This turns out to be surprisingly difficult to look up. Maybe I'm looking in the wrong places, but I'm having difficulty finding out how commonplace one inch of rainfall in an hour is or what it actually looks like in practice. A lot of information about rainfall averaged over a month, and the Met Office classify rainfall greater than 4 mm per hour as "heavy", but don't say how common "heavy rain" according to this criterion actually is.
What does 1 inch of rain per hour mean in practice, how often does that much rain or more happen (say, in the UK), and what would it do to a field of crops?