flash flood vs flooding

flash flood

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

flooding

noun
  • An act of flooding; a flood or gush. 

  • A form of therapy that treats a phobia by suddenly exposing the patient to the object of the phobia, instead of approaching it gradually. 

  • Emotional overwhelm sometimes leading to a primal state of rage or panic. 

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