Study says L.A. flood risk is far greater than expected

Flooding from a storm event so severe it only occurs once every 100 years would cause far greater damage to life and property in the Los Angeles Basin than federal emergency officials projected, according to researchers at UC Irvine, who are also warning Black and low-income communities would be hardest hit by the disaster.

“We found that nearly 1 million people live in areas that could be at risk from a 100-year flood,” said Brett Sanders, professor of civil and environmental engineering. “That’s about 30 times more people at risk than suggested by the Federal Agency for Disaster Management.”

The study, published Monday in the journal Nature Sustainability, does not predict when the next 100-year flood will occur. But the paper is among the first to examine how extreme weather events caused by climate change may affect the Los Angeles Basin — a region whose development has been guided by deep social and racial divisions that favored white residents.

In the Los Angeles Basin, researchers found that Black, Hispanic, and Asian residents were 79%, 17%, and 11% more likely to experience waist-high flooding than White residents, respectively.

That’s because a 100-year flood rendered the region’s key waterways — the Los Angeles River, Dominguez Channel, Compton Creek, and San Gabriel River — as well as drainage systems originally built seven decades ago, unlivable for the region to make could quickly become overwhelming, researchers say.

Since that time, the study says, massive urban sprawl has greatly reduced the amount of unpaved land available to accommodate the runoff of powerful atmospheric flows driven by climate change.

“Our goal is to highlight communities where flood risk is disproportionately high,” Sanders said, “and provide important data to protect lives and livelihoods and to plan and design cost-effective and equitable flood adaptation responses.”

A view of the Los Angeles River in Long Beach.

A view of the Los Angeles River in Long Beach.

(Allen J. Schaben/Los Angeles Times)

Federal disaster agencies decades ago designated a low-lying zone stretching 75 miles from Pico Rivera to Long Beach as a “special flood risk area” at risk of flooding during El Nino storm conditions if the aging system didn’t is improved.

Homeowners with government-backed loans in such areas are required to purchase flood insurance. But the study says property owners outside of that may find flood insurance unnecessary.

If the study’s worst-case projections prove true, many low-lying impoverished communities near the region’s aging system of dams, debris basins, storm drains, levees and shaped river channels — and outside of federally designated flood zones — could be under six feet Water.

The study’s unprecedented combination of high-resolution flood modeling and socioeconomic data also predicts that “such inequalities are likely to be compounded by the challenges and costs of navigating the numerous federal, state and local governments that allocate resources to flood mitigation” and recovery .

UCI researchers’ analysis of data from 1,767,588 parcels of land within approximately 2,700 square miles shows that approximately 874,000 people and up to $108 billion in property, stretching south from the Santa Monica Mountains to Long Beach, are at risk of flooding.

Major flooding would occur between the Dominguez Canal to the west and the Los Angeles River to the east, some of which would push into the communities of Carson, Paramount, Compton, Bell Gardens, South Gate, North Long Beach, and parts of downtown Long Beach, including the south end of Pine Street near the Long Beach Convention Center.

People sit under a tree in DeForest Park near the Los Angeles River in North Long Beach.

People sit under a tree in DeForest Park near the Los Angeles River in North Long Beach.

(Allen J. Schaben/Los Angeles Times)

Long Beach alone, the study found, has an exposed population of 88,000 to 262,000 people who are disproportionately black and disadvantaged. Nearby Paramount has an exposed population of 15,000 to 53,000 people with a similar demographic profile.

In such areas, the study says, flood recovery is “often lengthy and incomplete” because of support for flood risk reduction projects and disaster recovery programs that tend to benefit more affluent communities.

The entire 51-mile-long LA River flood control channel was built in 1938 in response to destruction by a major flood. It was designed to serve three main purposes: preventing floods from destroying life and property, managing discharges from sewage treatment plants, and flushing stormwater into the Pacific Ocean as quickly and efficiently as possible.

Since then, a combination of new high-resolution weather models and existing climate models has shown that the risk of a “megaflood” increases as global temperatures rise due to climate change, which began in earnest a century ago.

The new climate predictions, published in the UC Irvine study, show that massive flooding in the Los Angeles Basin would disproportionately damage low-lying black and poor neighborhoods.

“We are seeing complex flooding patterns with some locations deep in the water and others shallow,” said Jochen Schubert, research specialist in geomatics and flood risk at UC Irvine. “So one idea is to put homes three or more feet up on stilts in flood plains.”

“It also makes sense,” he added, “to warn high-risk neighborhoods so they start putting up electrical outlets and taking action to prevent floodwaters from corroding drywall.”

Long Beach officials have dismissed such suggestions — at least for now. They say it’s equally unrealistic, considering the cost of adding stucco to a modest single-family home ranges from $50,000 to $100,000.

“We may have specific flood-related requirements in future construction,” said Christopher Koontz, acting director of Long Beach’s development services division. “But many of our existing homes along the flood defense channels are more than 100 years old and we are in the midst of a housing crisis.”

“Unless it’s paid for by the government,” he added, “we’re not going to raise thousands of residential buildings.”

A more pressing concern is what Mark Pestrella, director and chief engineer for the Los Angeles County Flood Control District, described as “rain from one of these crazy new storms that’s coming down in some neighborhoods and along some freeways hard enough for our drainage systems to handle.” I can’t get rid of all that water fast enough.”

Long Beach recently adopted a new “Comprehensive Plan to Combat Climate Change” to focus post-disaster relief efforts on “low-income and communities of color” in areas including “along the Los Angeles River Channel where the risk urban flooding is expected to increase.”

On a recent morning, Koontz pointed to hundreds of modest stucco homes being built along a southern stretch of the Los Angeles River canal that empties into Long Beach Harbor.

“The stormwater system here isn’t big enough to handle a large amount of rain,” he said, shaking his head. “If this area was under water for months – forget it, we would have to demolish everything.”

“So this area needs some help,” he added, “but it’s going to take time.”

Eric Tate, an associate professor at the University of Iowa and an expert on social vulnerability to flooding, said the study reflects a belated concern in the nation — as inland flooding continues to increase due to climate change, the impact on lower areas is disproportionately decreasing . Minority Income Communities.

“This is a big step towards incorporating social justice into our flood risk thinking,” Tate said. “Imagine if that were something we care more about and have redesigned.”

But interviews with local residents suggested some weren’t overly concerned.

“I’m not really worried about a future flood,” said Alex Navas, 48. As he spoke, Navas was trimming a hedge next to the house he moved into three years ago. “It’s like all the warnings about a big earthquake – but who really knows when that’s going to be?”

Then there was Nick Paccione, 65, a lifelong resident of the area, who said he was at least vaguely aware of the risk of flooding.

“Most people here,” he added with a smile and a shrug, “are more concerned with holding on to their jobs and keeping their heads above water — no pun intended!”

Times contributor Lorena Iñiguez Elebee contributed to these graphics.

https://www.latimes.com/environment/story/2022-10-31/study-says-l-a-flood-risk-is-far-greater-than-anticipated Study says L.A. flood risk is far greater than expected

Alley Einstein

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