expression
when it comes to ...; where ... is concerned
Follows a noun and introduces a topic, often implying that the situation naturally leads to a certain result or characteristic.
彼となると、話が長くなる。
When it comes to him, the conversation gets long.
日本の夏となると、やはり花火大会ですね。
When it comes to Japanese summer, it's definitely the fireworks festivals.
expression, conjunction
if it turns out that ...; in that case
Follows a clause and presents a hypothetical or realized condition, often with a sense of 'if that's the situation'.
明日雨となると、試合は中止だ。
If it turns out to be rainy tomorrow, the game will be canceled.
彼が来ないとなると、計画を変えなければ。
If it's the case that he isn't coming, we'll have to change the plan.