Record-breaking rainfall and flooding paralyzed New York City on Wednesday, exposing the city’s vulnerability to heavy downpours that are becoming increasingly more severe with global warming.
As the remnants of Hurricane Ida swept through the New York area, Central Park recorded 7.19 inches of rain, nearly double the previous record set in 1927 for the same date, according to the National Weather Service. New York City issued its first-ever flash flood emergency alert as furious, wind-driven rains swamped the subway system and led to at least eight deaths.
More intense downpours are a telltale signal of a hotter planet. For every 1.8 degrees Fahrenheit of global warming, scientists have found, the atmosphere can hold about 7 percent more moisture. That means much heavier rainfall when storms do occur.
Across the continental United States, the heaviest downpours have become more frequent and severe in recent decades, according to the federal government’s National Climate Assessment. The Northeast has seen 50 percent more rainfall during the heaviest storms compared with the first half of the 20th century.
New York City is particularly vulnerable to flooding from huge storms. Three-fourths of the city is covered by impervious surfaces like asphalt, which means runoff is channeled into streets and sewers rather than being absorbed by the landscape. And the city’s century-old subway system was not designed for a warming climate. Even on dry days, a network of pumps pours out 14 million gallons of water from its tunnels and stations. Heavy rains can overwhelm the system, as they did on Wednesday.
The Metropolitan Transportation Authority has invested $2.6 billion in resiliency projects since Hurricane Sandy inundated the city’s subways in 2012, including fortifying 3,500 subway vents, staircases and elevator shafts against flooding. Still, this week’s flash floods showed that the system remains vulnerable.
Scientists are now able to quantify the role that climate change plays in any particular extreme weather event. While it is still too early for an analysis of Ida, researchers last month determined that violent and deadly downpours in Germany and Belgium in July were made 1.2 to 9 times more likely by global warming.