intensify vs richen

intensify

verb
  • To become intense, or more intense; to act with increasing power or energy. 

  • To render more intense 

richen

verb
  • To gain richness; become heightened or intensified in brilliancy. 

  • To make or render rich or richer. 

  • To become rich or richer; become superior in quality, condition or effectiveness. 

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