Los Angeles Flooding Risks Are Disproportionately High For Lower-Income Communities

As Los Angeles braces for the first big storm of the season, a new study reveals that the city’s flooding risks are far greater than federally defined floodplain maps indicate. And those risks are disproportionately high for lower-income communities, highlighting the need to consider equity as a key part of climate resilience.

The results, published Monday in Nature Sustainability, come from a new, high-resolution flood modeling platform that assesses risk at every 10 feet across a 2,700-square-mile area. Developed at the University of California, Irvine, the framework connects hazards from rainfall, stream flow and storm tides with demographic data on population density, race and economic disadvantage. It allows users to view flood exposure and vulnerabilities based on their current location or for a 30 year time frame. The platform has the potential to transform flood risk management by enabling communities to understand their unique needs and identify opportunities for reducing vulnerability and risks.

While the common image of flood risk is movie-star beach houses along the Malibu coast, most Angelenos live in areas that are at risk of being hit hard by a “100-year” flood — an event with a 1 percent chance of occurring in any given year. But those who are most vulnerable to flooding LA flooding risks also experience the greatest hardships from the impacts, including the disruption of daily life and the loss of economic well-being from damage on property. “These events are not democratizing,” said Brett Sanders, one of the researchers behind the study. “They hit the poor hardest.”

The difference between the government’s assessment of flood risk and that of the scientists is in part due to the city’s aging water infrastructure, the researchers say. The city’s many flood channels are clogged with sediment and vegetation, which limits their ability to carry runoff from heavy rains. The new assessment uses lidar technology to survey the city’s waterways and to model their performance in a severe storm.

According to the authors, those findings reveal that more than 200,000 properties have a moderate chance of being severely affected by flooding in 30 years, which means they would lose access to utilities and other essential services. The study indicates that a significant portion of those properties are located in low-income, historically marginalized communities, raising concerns about the social impact of flooding.

Although sea level rise is a major contributor to flooding in coastal regions, the vast majority of Los Angeles floods are caused by localized precipitation. These floods are triggered by extreme rainfall and flash flooding from overflowing streams and tributaries, as well as atmospheric river events driven by climate change.

To help address these issues, First Street is partnering with a number of communities to develop local climate action plans that focus on building resilience and addressing flood risks in the most vulnerable areas of their neighborhoods. This includes leveraging local assets such as parks and school grounds to create resilient neighborhoods. The county is also working to build a more equitable and transparent approach to flood risk management.