Hi there -- /u/restricteddata has written on this before, and while there were generic warning leaflets dropped on many Japanese cities that were conventionally bombed, there were not warning leaflets dropped on Hiroshima, and those dropped on Nagasaki were dropped after the city was bombed.

https://www.reddit.com/r/AskHistorians/comments/2z7wt6/ive_been_doing_a_lot_of_research_and_cannot_come/

https://www.reddit.com/r/AskHistorians/comments/69st74/why_did_the_us_decide_to_bomb_civilian_cities/

https://www.reddit.com/r/AskHistorians/comments/7wo0di/is_it_true_that_the_us_dropped_flyers_around/