aridity vs dry spell

aridity

noun
  • A long-term lack of rainfall or moisture. 

dry spell

noun
  • A drawn-out period where the weather has been dry, for an abnormally long time; shorter and not as severe as a drought. 

  • A period or time where there is little activity, productivity, low income etc. 

  • A period of time without sexual intercourse. 

How often have the words aridity and dry spell occurred in a corpus of books? (source: Google Ngram Viewer )