に伴って / に伴い【にともなって / にともない】

に伴って means "along with", "as": when one thing changes or happens, a second thing comes with it. It goes after a noun for a change or an event – ぞうか増加, はってん発展, こうじ工事 – or after a verb in the dictionary form plus の. ともなう伴う means "to accompany".

Before a noun it becomes に伴う.

"Due to" in notices

With a single event – construction, an update, a new law – に伴い gives the cause of a change. This is the use you see on signs and in official notices.

に伴って or につれて

につれて is only for gradual change: as one thing moves step by step, so does the other. に伴って covers that too, and also a single event that brings a consequence.

• × 地震につれて、津波警報が発令された → 地震に伴い、津波警報が発令された

Register

に伴って is formal and written; に伴い is the more formal of the two and the usual form in news and announcements. In conversation, につれて or といっしょに一緒に is more natural.