Green’s Dictionary of Slang

dry, the n.

(Aus.) the dry season.

1938		(con. 1941) X. Herbert Capricornia (1939) 74: The Dry! the good old Dry — when the grasses yellowed, browned, died to tinder.
1949		I.L. Idriess One Wet Season 22: With the Dry come plentiful fruits.
1955		N. Pulliam I Travelled a Lonely Land (1957) 233/1: Dry, the – the long period without rainfall in the north of Australia.

In phrases

on the dry (adj.)

(Irish) eschewing alcohol, teetotal.

2015

L. McInerney Glorious Heresies 154: ‘[H]e’s on the dry and he’s trying not to be a prick’.