flash flood vs inundation

flash flood

noun
  • A sudden, rapid flood, usually of short duration and local impact. 

inundation

noun
  • The state of being inundated; flooding 

  • The act of inundating; an overflow; a flood; a rising and spreading of water over grounds. 

  • An overflowing or superfluous abundance; a flood; a great influx 

How often have the words flash flood and inundation occurred in a corpus of books? (source: Google Ngram Viewer )