expression, godan verb (-ru)
the New Year begins; the year changes
Used to mark the transition from one calendar year to the next, often in formal or seasonal contexts.
年が改まって、新しい気持ちで仕事を始めた。
The New Year began, and I started work with a fresh mindset.
年が明ける also means the New Year begins, but focuses on the old year ending and the new one dawning, while 年が改まる emphasizes the formal change of the year.
A set phrase combining 年 (year) with 改まる (to be renewed, to change formally). The expression is transparent and follows standard grammar.