flash flood vs submersion

flash flood

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

submersion

noun
  • The act of submerging, or the state of being submerged; immersion 

  • A differentiable map whose differential is everywhere surjective. 

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