Flooding can be devastating to people and communities, disrupting lives, damaging property and destroying businesses. It can also leave behind dangerous, unsanitary conditions and create dangerous health hazards, especially for those living in lower-income areas. When floods hit, those communities are often left to deal with the consequences alone – not only for their homes but also for their livelihoods and economic stability. For example, hourly workers are more likely to lose pay when their jobs are disrupted by flooding and cannot get to work; low-income residents are less able to cover the costs of recovery; and children are especially vulnerable to contaminated drinking water and overheated indoor spaces.

While many Angelenos think of the flood risk as affecting wealthy coastal neighborhoods like Malibu, a much larger percentage of Los Angeles is flooded by 1-in-100-year or higher rainfall events. The city’s aging waterway control system has been unable to keep pace with these large deluges, causing the majority of flood risks to be concentrated in inland communities.

The city’s current flood hazard maps are outdated and insufficient to capture the real potential of these storms, according to new research by University of California, Irvine (UCI) Los Angeles flooding risks scholars published in Nature Sustainability. The team used a cutting-edge computer modeling flood simulation program called PRIMo to model a range of flood scenarios and show in house-by-house detail how people across the city would be affected by a severe flood.

Current FEMA directives require mapping of fluvial (river) and coastal (storm surge, waves) hazard zones but not pluvial (rainfall) hazards. However, as a result of urbanization, Southern California is filled with vast areas where rain runoff can’t be contained by streets and gutters and flows into rivers, streams and tributaries. The current models use a standard of flood peaks and channel capacities that are not realistic for the LA area.

This overestimate puts 197,000 Angelenos at risk of waist-deep flooding during a 1-in-100-year flood, and the researchers found Black, Latino and Asian residents are 79%, 17% and 11% more likely to experience flooding to this extent than white residents. This is because these communities are closer to creeks and rivers, have more vegetation on the land that can absorb rainwater and evaporation, and have had major infrastructure investments that have not kept up with development.

The team is exploring solutions, including green and gray infrastructure that can better manage floods by addressing the source of the problem rather than just building walls and levees to block flood waters. These strategies are more affordable and sustainable than traditional grey infrastructure, but they require a significant upfront investment to be effective. In addition, a broader effort is needed to educate and inform residents of their local flood risks and how to prepare for them. One way to do this is through a motion sponsored by Councilmember Janice Hahn, which calls for an assessment of the city’s stormwater systems with an equity lens and the implementation of “community-based resilience measures” for those most at risk.

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