By A city that has adapted to rising sea levels and flood threats from climate change faces a new danger: severe flooding. Hundreds of thousands of people live in parts of Los Angeles that could be inundated by at least a foot of water during a so-called 100-year flood event, which has a 1 percent chance of occurring in any given year. And, according to a study by researchers at the University of California, Irvine, those at greatest risk are Black residents.
The UCI study, published in Science Advances, uses a new methodology to assess flood flooding risks Los Angeles risks. FEMA’s guidelines call for mapping fluvial (river) and coastal (storm surge, waves) hazards but not pluvial hazards (rainfall). The new study uses computer models to subject the city to a 24-hour flood of rain at levels that would be expected during a weeklong storm with heavy runoff from urbanized land surfaces. Such rainfall would be more likely to overwhelm aging drainage systems than flooding caused by rivers or by storm surge and waves.
These models show that if such a storm hit today, 197,000 to 874,000 people and $108 billion in property would be at risk. This is far greater than the 50,000 residents and $50 billion in property identified by the city. The researchers estimate that the most vulnerable are in neighborhoods near tributaries and small waterways that overflow during flood events. These areas are more at risk from rainfall and flash floods than those closer to the coast that are typically affected by the more common flooding from storm tides and waves.
Many of these communities are low-income, and the most disadvantaged residents are Black. Ulibarri’s study finds that non-Hispanic Black Angelenos are 79% more likely than white Angelenos to experience waist-high flooding during a 100-year flood. Hispanics and Asians are also more at risk than whites, but the differences are less stark.
Los Angeles officials say they are already working to prepare for a future of increasingly severe floods and rising seas, including holding public workshops on the issue and updating their flood maps. The county’s disaster-response director, Eric Pestrella, says workers are also going door to door in flood-risk neighborhoods to raise awareness about the risks and to offer tips on how to retrofit homes. “We believe the best way to protect homes from floods is for residents to have the information they need, and that includes learning about their risks, buying flood insurance and taking action,” he said. He added that the city had also been helping residents adapt to their higher risk by offering free flood-proofing materials. UCI’s Sanders hopes other cities will replicate this approach and take a closer look at their own data to identify the most vulnerable residents. “Communities that adapt to higher risks can limit damage and lower their flood insurance costs,” he said. “And, that’s a win for everyone.” This article was originally posted on Oct. 24, 2018, at 6:55 a.m.
