On a cloudless morning two years ago, shortly after Danielle Smith moved into a new apartment in Far Rockaway, Queens, she looked out of her window and saw a swan gliding by.

Overnight, the street in front of her home had become a creek.

That morning, Ms. Smith, a 36-year-old mother of five, learned that she was living in one of the most vulnerable areas in the city to high-tide flooding.

A hundred thousand New Yorkers currently live in low-lying coastal neighborhoods affected by chronic flooding. About half of them, like Ms. Smith briefly, reside in the working- and middle-class enclaves surrounding Jamaica Bay.