11 Climate Action but cities in California have compounding risks. They face increasing flood risks while also managing drought and wildfires. “You look back at the last few years in this state — it’s been fire to ice, and no warm bath in between,” Governor Gavin Newsom said during a news briefing on March 15, 2023, in Pajaro, the Monterey County town flooded by a levee breach. The flooding displaced hundreds of people in the primarily migrant town and raised concerns about crop yields in the agricultural region. If anyone has any doubt about Mother Nature and her fury—if anyone has any doubt about what this is all about in terms of what’s happening to the climate and the changes that we’re experiencing—come to the state of California. — Governor Gavin Newsom In California, as elsewhere, the challenge is compounded by a basic problem: inadequate understanding of flood risk. One study of flood exposure in Los Angeles that appeared in the journal ScienceAdvances in August 2022 suggests that the population exposed to dangerous flooding, or a flooding event with 1 percent annual probability, is between 10 and 40 times greater than US government maps show. The study, published in November 2023 in Nature Sustainability, estimates that 425,000 people and $36 billion of assets would be exposed to dangerous floods rising to a height over 30 cm within the 100-year flood zone. The study also shows that the current 1 percent annual probability flood cannot be contained by existing flood infrastructure such as levees. The numbers of at-risk Angelenos surprised even the researchers. “We double- and triple-checked our models and tried to figure out, Did we make a mistake?” said Brett Sanders, director of the Flood Lab at the University of California, Irvine. To make their estimates, Sanders and his colleagues used an innovative geospatial modeling approach specifically designed for high-performance computing, allowing them to achieve an unprecedented level of mapping detail. Initially, the researchers set out to learn which Angelenos face the biggest flood risks by combining new hazard maps with census data. As they expected, they found an inequality along socioeconomic lines, with the more disadvantaged half of the population shouldering 65 percent of the composite flood hazard. But the strongest disparity they found was racial. Although non-Hispanic White communities were disproportionately likely to suffer coastal flooding, Black, Hispanic, and Asian residents were 79 percent, 17 percent, and 11 percent more likely than White populations, respectively, to be exposed to dangerous flooding, particularly from river floods. The racial and economic disparities, previously unacknowledged in federal flood risk maps, are exacerbated by the fact that disadvantaged communities tend to receive less government support for flood risk reduction and disaster recovery compared with more affluent communities. Left unaddressed, these risks only grow, leaving communities not only unprepared but less capable of bouncing back after a storm, says Sanders. The six most expensive natural disasters in the world in modern history were all the result of tropical storms such as Hurricane Katrina. And years later, some communities are still recovering from previous disasters even as they try to prepare for future storms. “New Orleans tells the story of cities that don’t recover, neighborhoods that are forever changed after the flood, that don’t bounce back,” Sanders says.
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