What happens after the stations are sealed from the floods?

この東京メトロのポスターとアニメを見ましたか。大きい洪水の場合に、駅を密封します。けれども、出られそうにないです。この後でどうしたらいいのでしょう。イラストもアニメかわいいですが、状況はこわいです。

There are posters in the Metro explaining how prepared they are for floods. There’s an even creepier animation of people moving through Tokyo streets and subway passages, while agents shut the station entrance, air vents are closed, and the tunnels themselves have giant walls to prevent the floods from surging into the station.

I think we’re supposed to feel that the Metro is ready for emergency. Instead, I wonder what type of global warming could cause all that water in the stations. And once we’re all safely sealed inside the stations, then what? Eventually the convenience stores and vending machines will run out! Not to mention the closed air vents.