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warming waters

Los Angeles’s Floods Show Why Sewers Matter

Recent atmospheric rivers are a preview of what will become much more common as climate change accelerates.

People look over a fence at the swollen Los Angeles River.
Mario Tama/Getty Images
The Los Angeles River, swollen by storm runoff as a powerful atmospheric river storm, the second in less than a week, continues to hit Southern California, on February 5

The Los Angeles River is often little more than a trickle as it winds downtown on its way through Long Beach to the Pacific. But this week, it threatened to overflow its concrete banks. Neighborhoods found themselves under feet of water. Mudslides took out hundreds of trees and dozens of buildings, flash flooding swept cars away, and at least three people have died.

Many parts of California received more than 10 inches of rain in little more than a day, bringing the entire region to a standstill. Los Angeles Mayor Karen Bass declared a state of emergency as some areas were evacuated; she interrupted a press conference to take a call from President Biden, who offered federal assistance.

The storms, which continued through Tuesday and had tens of millions of people under flood watches and warnings, again show how unprepared many places are for the climate crisis: The warming atmosphere can hold more water, meaning it can drop more of it on us all at once. And while some types of infrastructure get all the press when it comes to climate change—think sea walls or levees, the big aboveground projects that can either stand up to a hurricane or fail spectacularly—the flooding in Los Angeles, San Diego, and other cities is a reminder that the more mundane urban systems are also dangerously outdated in the face of a rapidly warming planet.

“Things like sewers and drainage systems, we tend to take for granted,” said Mikhail Chester, a professor and director of Arizona State University’s Metis Center for Infrastructure and Sustainable Engineering. Levees and sea walls are often built with catastrophic events in mind, like a 50- or 100-year flood with only a small chance of occurring each year. But the storm drain under most residential roads is capable of managing only something like a five- or 10-year event, if that, and is likely rapidly aging into a rusting obsolescence. That’s before we address the fact that climate change is turning 100-year floods into 50- or 20-year floods, and a three- or five-year flood into, say, a particularly wet Tuesday.

The “atmospheric river” dropping water on California is also being juiced by El Niño, the Pacific Ocean weather pattern that changes precipitation patterns and generally warms the globe. El Niño will likely get stronger in a warmer climate, research has shown. All this adds up to dated and underpowered drainage systems in cities in California and across the country, and an unclear and very expensive path forward.

“The challenge with the rain events in California is that this is a pretty extreme precipitation event causing massive amounts of runoff,” said Lauren McPhillips, an assistant professor of civil and environmental engineering at Penn State, adding that existing infrastructure simply isn’t built to handle anywhere near this volume of water. “In these more extreme, larger storm events, we need to think bigger about our whole system and get more creative with our planning.”

The reason the sewers and storm drains aren’t built for anything even close to the catastrophe unfolding in California is largely thanks to cost—huge pipes under every street never made sense, and still don’t even as the climate changes. But despite the cost and the relative lack of charisma of your standard drainpipe, experts and policymakers are aware of the risk.

“Certainly, infrastructure that is belowground may be forgotten by many folks, but I can guarantee you that engineers are thinking about it all,” McPhillips said. “The challenge with underground infrastructure is that it is extra challenging to access and update or fix. It’s also costly to consider increasing the size of an entire storm sewer system.”

The primary way to address risks to sewage and drainage systems is the same as it has been for 100 years, Chester said, using a sort of Gladiator-adjacent mantra: “Robustness, hardening, strengthening, armoring.” If you take an aging, small pipe, and make it newer, larger, and stronger, you reduce flood risk. But when 10 inches of rain can fall across most of California in a day, the limits of the traditional approach become clear.

“The reality [is] that you simply can’t rehabilitate everything under the ground … for climate change, you simply can’t,” Chester said. “So a reasonable strategy seems to be to attenuate, reduce the amount of water that’s putting pressure on those systems.” In other words, if the pipes can’t all be swapped out for jumbo-size warming-proof behemoths, try to limit the amount of water that gets to the pipes. One way to do that is with green infrastructure.

“There is growing interest in the U.S. and around the world in nature-based solutions, including green stormwater infrastructure,” McPhillips said. She has documented the increasing use of things like green rooftops, curbside “swales” where plants and soil can collect water, and larger retention areas—all designed essentially to soak up some of the intense rainstorm’s output and then release it slowly, such that the existing drainage systems don’t get overwhelmed.

Notably, though, the adoption of those ideas varies widely—for example, in McPhillips’s research from a few years ago, Portland, Oregon, had built up 10 times as much “green stormwater infrastructure” as Baltimore or Phoenix. “In general, the implementation of green infrastructure in the U.S. is moving slowly,” said Hassan Davani, an associate professor of civil, construction, and environmental engineering at San Diego State University. Much of the need is on private land, and incentives may need to be developed to convince those private landowners to put in the rain barrels or gardens.

Another strategy beyond improving the pipes and letting nature stand in the way is to, more or less, let a flood happen—strategically. Known as “safe to fail,” the premise is to acknowledge that certain areas of a city will likely flood periodically and to prepare for, and hopefully reduce, the impacts of those floods. The famously low-lying Netherlands led the way in recent years with its Room for the River program. Domestically, Phoenix has focused on this idea, essentially setting aside certain areas that lack robust drainage systems to bear the brunt of the flooding when the monsoon rains come through.

All of these reforms struggle to get attention next to bigger projects. A new sewer pipe rarely gets a headline; a proposed $6 billion sea wall in Miami or a—gulp—$119 billion structure trying to keep New York above water sure does.

Still, with the issue becoming increasingly clear, money has started to flow toward the sewers and related projects. The Bipartisan Infrastructure Law, passed in 2021, contains billions in funding for climate-impacts management, including some focused on storm runoff and flooding.

Chester said he is optimistic in the face of frankly long odds for these systems. “At the city level, you see remarkable innovation,” he said. “Are they keeping up with the problem? No, absolutely not. Because it’s not a problem you can keep up with.”

The Midwest and Northeast are expected to see days with at least two inches of rain increase through the middle of the century. California could have 25 percent more overall precipitation in 2080 than it did in 2005. One-third of the entire U.S. population might see a supposedly 100-year flood three times in their lives, according to a study published in December.

As California weathers this latest storm, it is clear again that people and governments need to start thinking about system-level changes, rather than individual (if expensive) “Band-Aid” solutions. “I do not believe there is much difference between glamorous and nonglamorous parts of the stormwater system, in terms of receiving attention,” Davani said. “The whole system needs more attention, i.e., more funding, to keep up with the new climate.”