all year round; year after year
Emphasizes that something continues throughout the entire year, or happens repeatedly every year without fail.
This shop is bustling with tourists all year round.
He is constantly swamped with work year after year.
A fixed adverbial expression composed of 年 (year) + が (subject marker) + 年中 (all year). The exact historical derivation is uncertain, but it likely developed as an emphatic way to say 'throughout the year'.