Why did John the Baptist preach repentance through water baptism and specifically how is that different than repentance through ashes and sackcloth?

Are there any records that explain why baptism was used for repentance when the Jews already had a method of repentance by putting ashes on them and wearing sackcloth? This seemingly worked as noted in various parts of the bible (e.g. Ninevites in book of Jonah) What made repentance through baptism unique?