Why the New York Subway System Keeps Flooding

For many New Yorkers, the waterlogged subway stations around the city on Monday night were a familiar disruption to their commutes.

Though service returned to normal by Tuesday morning, the storms that struck the region served to highlight — once again — just how overmatched New York City’s subway system is by the increasingly extreme weather caused by climate change.

The subway system, which is more than a century old, is relied on by millions of passengers every day and weaves the five boroughs into a singular city. But it has a longstanding infrastructure problem that is only getting worse as rainfall gets heavier and more frequent.

Even as some improvements have been made, the M.T.A. is in a race against time; in 25 years, the likelihood of torrential rainfall events in the region is projected to almost double.

Twenty of the 472 stations in the sprawling subway network had to be temporarily closed on Monday night, including bustling stops along the 1, 2, 3 and 6 lines in Manhattan, which run the length of the island and link to the Bronx. There were widespread service delays as water sloshed onto busy tracks and platforms. Amateur video footage showed streams of water flowing through the 23rd and 28th Street stations, on the 1 line.

Bored through layers of dense bedrock, the subway system is surrounded by the groundwater that runs beneath the city. Even on a dry day, transit workers are routinely dispatched to plug leaks and pump out typically between 10 million and 13 millions of gallons of water from the system, according to the Metropolitan Transportation Authority, the state agency that operates the city’s mass transit system. On Monday night, transit workers pumped out more than 15 million gallons of water from the system, in part because the city’s sewage system backed up, the M.T.A. said.