The answer is A. Rapid Spring Snowmelt
Light rain over a large area simply not gonna causing any flood. Rapid spring snowmelt on the other hand is one of the major cause of floofs. Snow is basically a water which take forms in a more solid substance. If the snow is located in higher grounds, it tend to send flood to the lower ground when it melts.
Thats why we usually evaporate it through heat. One of the area in the united states that suffer from Rapid Spring Snowmelt is Alaska.