Millions of people rely on subways for transportation. But as the world warms, climate-driven flooding in subways is becoming more and more common. NPR correspondents Lauren Sommer and Rebecca Hersher talk about how cities across the world are adapting. For more of Rebecca's reporting on climate-driven flooding, check out "NYC's Subway Flooding Isn't A Fluke. It's The Reality For Cities In A Warming World."(https://www.npr.org/2021/09/02/1021185475/climate-change-means-more-subway-flooding-worldwide-like-new-york-just-experienc)You can follow Lauren on Twitter @lesommer and Rebecca @rhersher. Email Short Wave at ShortWave@NPR.org.