A new scientific study has found that hundreds of thousands of people in Los Angeles could have been flooded by at least a meter in a 100-year disaster, highlighting the dangers of aging infrastructure in the area. America’s second largest city.
This is an estimate of flood exposure in Los Angeles that is much higher than the estimate released by the federal government. That estimate classifies areas of the city with about 23,000 residents as at high risk for a 100-year event or an event with a 1% chance of occurring in any given year.
The report’s lead author, Brett F. Sanders, professor of civil and environmental engineering at the University of California, Irvine, says the discrepancy is partly explained by the new study’s more realistic look. the city’s water infrastructure.
Many of Los Angeles’ flood control channels have become clogged with sediment and vegetation, reducing the amount of water they can transport, Dr. Instead of assuming the channels were as good as new, he and his colleagues used survey data collected with lidar, a technology that creates detailed 3-D maps, to check if the lines How serious would a city’s waterways handle a storm in their actual state?
“Don’t assume perfect performance from our infrastructure; consider the most probable performance,” said Dr. Sanders. “When we did this in Los Angeles, the second largest city in the United States, the risk was actually greater than what FEMA said,” he said, referring to the Federal Emergency Management Agency. state.
Other major cities face similar dangers. Previous years Deadly floods in New York from the remnants of Hurricane Ida emphasized the need to Clearing sewers and expanding sewage pipes so that the torrential downpours can quickly wash away.
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FEMA declined to comment directly on research, published Monday in the journal Nature S Sustainability. In a written statement, David I. Maurstad, senior executive director of the agency’s National Flood Insurance Program, said all homeowners should learn about flood tolerance to their assets, whether or not they live in areas that FEMA deems high risk.
“When it comes to flood risk, we know: Where it can rain, there can be flooding,” he said.
Extreme droughts and wildfires could be climate threats that have been on the minds of Californians in recent years. However, because hotter air can carry more moisture, global warming also exposes the state to more intense winter storms – in particular, ocean-borne storms called atmospheric rivers, named for their long, sinusoidal shape and huge amount of water. they convey.
Rivers with temperate atmospheres generally provide California with most of the rainfall it receives. But rapid succession of strong floods can cause catastrophic flooding, as happened in the winter of 1861-62, when relentless rain and snow across California and the Pacific Northwest destroyed houses and turn valleys into lakes.
Today, California has about a 1 in 50 chance each year of experiencing another weeklong hurricane of equal magnitude, Scientists recently estimated. They found that global warming has nearly doubled this rate since a century ago. And, as the planet warms further, the risk will continue to increase.
Meanwhile, less intense storms will continue to cause disruption. In January 2021, heavy atmospheric precipitation from rivers in Southern California swept away a stretch of highway near Big Sur and caused dangerous streams of mud and debris on the hillsides consumed by wildfires. Estimated damage: 1.2 billion dollars.
Dr. Sanders and his colleagues estimated the flood risk in Los Angeles by precipitation for the city, in a computer model, with 24-hour precipitation in varying degrees, according to National Oceanic and Atmospheric Administration, there’s a 1 percent chance of it happening in any given year. They think this rain will not be able to seep into the ground, which can also happen if it comes in the middle of a week-long storm and the earth is saturated.
The researchers studied how water can move in the city by building a high-resolution topographic map, one that can show details as small as 3 meters, or about 10 feet. . This allows their analysis to take into account not only dykes and flood walls, but also for finer-scale infrastructure such as culverts and sewer pipes. They performed their calculations on a supercomputer in Wyoming operated by the National Center for Atmospheric Research.
The California Department of Water Resources and the Engineering Division of the Los Angeles Department of Public Works both declined when The New York Times asked if they would review the study prior to publication and comment on its findings.
Harrison Wollman, a spokesman for Los Angeles mayor Eric Garcetti, said the city has held public information sessions about flood risk and is working with FEMA and the Army Corps of Engineers to update the hazard map. flood. “This study will help better inform our efforts to prepare for an extreme weather event,” said Mr Wollman.
The study also found that Black and Hispanic residents were at disproportionate risk, largely in neighborhoods south of downtown Los Angeles near the Los Angeles River and the San Gabriel River.
Nicholas Pinter, an earth scientist at the University of California, Davis, who did not work on the study, said these are not the Angelenos commonly thought to be the most flood-tolerant. “The iconic and popular view of flood risk in LA is the beach houses of movie stars on the Malibu coast,” Dr. Pinter said.
Nícola Ulibarrí, an associate professor of urban planning and public policy at the University of California, Irvine and an author of the study, said disadvantaged communities often struggle more than others to cope. flood again. Their tenants are less likely to cover the cost of rebuilding; hourly workers are more likely to lose their income because flooding prevents them from going to work.
“If you look at the longer-term effects of recovery, those effects are also not evenly distributed,” says Dr Ulibarrí.
