Why drink sake under cherry blossoms?

From mid March to the end of April in Japan, you will see a lot of places crowded with people under trees of cherry blossom.Although it is true Japanese people love the appearance of cherry blossoms, the floral emblem of Japan, this practice is also grounded in ancient religious beliefs.Nowadays, sakura (cherry blossom) is a one word, but originally, it was a combination word, sa (sacred) + kura (a place where gods gather). It is said that the most admired god of ancient times was known as “Sa-god”.
So cherry blossoms were seen as a sacred place for gods to gather. It is believed that in ancient Japan, festivals were held under the sakura for the purpose of praying for good harvest and to invite those such as Sa-god from his mountain to paddy fields.
During the festivals, food and sake were offered to the gods, then consumed by worshippers. This custom of gathering under cherry blossoms continues today, though people have generally forgotten the history and instead just enjoy the beautiful flowers with food, sake and other alcoholic (and non-alcoholic) beverages. This custom is called hanami. Hana is the general term for flowers, but when used with mi (look), it specifically means cherry blossoms.

Writing Reference
Nishioka Hideo.(2009).Naze,Nihonjinha Sakuranoshitade sake wo nomitakunarunoka?(Why does Japanese want to drink sake under sakura tree? ).Tokyo.PHPkenkyusho(PHP Institute)　p19-21