Even an inch of rain, if it falls too quickly, can overwhelm a place.
This was a year of too much rain. It rained too much in the Northeast. It rained too much in the Pacific Northwest, where, after a hazy summer of record wildfires, record rainfall temporarily rendered Vancouver impassable by road or rail. On the Gulf Coast and in the mid-Atlantic, the wettest days keep getting wetter. This is one of climate change’s twisted bits of logic: Where it was dry, it was too dry. But where it was wet, it was way too wet.

In New York City, nearly 15 years after the mayor’s office began announcing bold strategies for climate mitigation and adaptation, the rain made a mockery of those plans. In July, 1.5 inches of rain fell in an hour, drowning streets and flooding social media with discordant images of people wading through inundated subway entrances to reach trains that were somehow still running. In September, the remnants of Hurricane Ida, which began its life as a tropical wave across the eastern Caribbean Sea, dropped more than six inches of rain on New York City in a few hours. Roughly half of that rainfall—3.15 inches—fell within the first hour.

An inch or two of rain might not sound like much. An inch of liquid in your standard shot glass, for example, would fill it roughly halfway. If that liquid were vodka, it likely wouldn’t even get you drunk.

But an inch of water in a more expansive container, say one the size of Central Park, works out to be more than 20 million gallons of water. On that scale, it’s easy to grasp how what feels like a small amount of rain can flood a city, especially when that rain falls quickly.

“When that two inches come in an hour as opposed to a day, there’s just no way for that water to seep into the soil to be absorbed into the landscape,” says Art DeGaetano, a professor of earth and atmospheric sciences at Cornell and a director of the National Oceanic and Atmospheric Administration’s Northeast Regional Climate Center.

If you’ve ever watered a potted plant, you have a sense of what DeGaetano means. Pour the water in too quickly, and the water overflows. But if you slow your pour by just a few seconds, the soil has time to absorb the water. Rain works the same way.

In cities like New York, which has far more asphalt and cement than earth, the bulk of the responsibility of absorbing the rain falls to sewage systems. But New York’s century-and-a-half-old sewer system was designed to handle no more than 1.75 inches of rain in a one-hour rainstorm. When rain exceeds that amount, or storms last longer, you get flooding.

When the water came, Edison Sainsbury wasn’t home. He’d been playing a show in Baltimore when Ida passed through New York City. By the time he’d made it back to the basement apartment in his family’s home in Canarsie, Brooklyn, “there was nothing we could do to get the water out quick enough,” he told me. It rose more than three feet, he estimates—roughly the height of an average 2-year-old.

In the Northeast, Ida’s rainfall killed more than 50 people, including 11 who drowned in basement apartments similar to Sainsbury’s. In Southeast Louisiana, where the storm made landfall, the death toll was lower—but the storm still hit hard, in other painful ways. More than 1 million people lost power, to start. Some still don’t have it back.

As an isolated incident, the storm would have been stark. But experts warn that across the country, including parts of the East Coast, the North and Midwest, and the Caribbean, climate change is making this kind of extreme precipitation happen more frequently.

“Even if you got the same amount of rainfall in the year, more of it comes in big events,” DeGaetano told me. “So instead of getting 100 events where it rains a half an inch, the extreme example would be you get 10 events that rain five inches. In the end, you have the same amount of water, but it comes in a very different way.”

This kind of flooding is distinct from flooding driven by wind and storm surges, when the ocean comes onto the land, as during Superstorm Sandy. This kind of flooding, the too-much-rain flooding, has become a recurring problem. The house where Sainsbury lives first flooded in 2019. Months into 2020 it happened again, and then again at the end of the year. And then Ida in 2021. The flooding from that storm has racked up, according to Sainsbury, more than $30,000 in out-of-pocket damages. The family didn’t have flood insurance, and when they tried to get it, they were told they did not qualify. Officially, the house isn’t in a FEMA flood zone. When Sainsbury spoke with a city employee, he asked about the flooding’s cause and was told, he remembers, that the pipes under the street simply couldn’t handle the amount of water Ida had dumped on the city. “The water had to go somewhere, and unfortunately that somewhere was in people’s homes,” he said.

One fix for that problem, a device called a backwater valve, allows water to leave the home but stops it from gushing back up the sewer line. The valve can cost a homeowner $1,000 to $2,000. And floodwater still has to go somewhere. A backwater valve doesn’t fix a sewer system designed for a fundamentally different climate.

New York City is upgrading its sewer system by installing pipes, for instance, closer to the surface that can help drain water during extreme events, Jainey K. Bavishi, the director of the Mayor’s Office of Climate Resiliency, told me. The city is also investing in ways of storing water during big rain events, transforming schoolyards and other open spaces so that they can absorb more water.

But the rate at which the city is adapting to these threats is lagging behind the speed at which rain is drowning it. In 2007—14 years before Ida—a storm dropped four inches of rain and snarled the subway in then-strange ways. It was the third significant storm that year; even then, experts widely acknowledged that climate change would make these kinds of events more likely. And yet the city’s report detailing which areas are at high risk of flooding from rain was released only in May 2021. After Ida, the publication The City noted that many of the people who had drowned in their home were in areas the report had marked as high risk. The city has planned an early-alert system, designed to notify the tens of thousands of people who live in basement apartments of dangerous rainfall, but it was not to be rolled out until 2023. (Post-Ida, the city has said it will speed up that timeline.) And during the pandemic, basic preventive measures, such as clearing sewer-drain gutters, have declined.

This kind of extreme rainfall is not going away—not in the Northeast, or the mid-Atlantic, or the Pacific Northwest. It is going to get worse. In the Pacific Northwest, climate models show that “our winters are liable to become wetter, and our summers liable to become drier,” Nicholas Bond, a climatologist at the University of Washington, told me. “And the increase in winter is greater than the decrease in summer.”

And for the Pacific Northwest there’s an added wrinkle. Moisture that used to fall as snow is now falling as rain. That’s part of why this fall’s floods were so severe early on—at least some of the rain fell on early-season snow, melting it and exacerbating the flooding. In coming years, even if the amount of precipitation stays stable, in the wintertime more “will fall as rain and come right down the hill, rather than as snow and stay there until the spring,” Bond said.

How to prepare for this kind of deluge? “Until you get hit, you just don’t realize how big it is,” Anais Roque, a postdoctoral research scholar at Arizona State University, told me. “It’s very hard to change people’s risk perceptions, because they haven’t experienced the event per se.” She understands that—it was the aftermath of Hurricane Maria that forced her to leave Puerto Rico for Arizona. And any one household can prepare only so much, she added: Communities need disaster contingency plans, including evacuation plans. If you have to leave, even temporarily, where would you go, whom would you go with, and how would you get there?

Even this kind of community-level preparation is a bit like the backwater valve. It can help you survive a disaster, but it doesn’t solve the underlying problems with how we think of disaster preparedness. Build Back Better, the infrastructure and climate-resiliency package that has stalled in the Senate, emphasizes physical infrastructure, Roque noted, and glosses over needed reforms in emergency management. After Ida, New York Mayor Bill de Blasio blamed the storm’s impact on poor weather forecasting and said the city would hire a private weather service for a second opinion. But the National Weather Service forecast was accurate, and warned that the region would receive as much as eight inches of rain. The problem wasn’t the forecast, but that the city failed to grasp the consequences of the warning, and that it rained too much too quickly, and that no one had a plan for dealing with that.