Floods cause massive damages and displace communities, often inequitably impacting low-income and minority neighborhoods. But how big are Los Angeles’ flooding risks? A new study finds that the area’s “hundred-year” risk of flooding is far greater than the federal government currently estimates, and is a disproportionate danger to Black residents in certain key areas.

The study’s authors used a unique method to model and visualize local inundation risk across LA County, which they call “hydroconditioning.” This process combines a sophisticated water-surface modeling tool with data from local governments, like shapefiles how big are Los Angeles flooding risks for stormwater infrastructure and path lines for pipes. The team then uses this data to test how well existing infrastructure would handle an extreme storm and the resulting flooding (Sanders et al. 2020).

These results highlight the need for improved, more equitable risk assessments and flood mitigation planning. In the future, these methods should be used to help communities identify and address vulnerabilities before a disaster strikes. They also serve as an important tool for understanding how a flood may affect people’s daily lives, especially when considering whether or not to invest in green and grey infrastructure, which can range from low-cost “green” strategies that reduce stormwater runoff to high-cost engineered structures like dams and levees (Lara et al. 2010; Lawrence et al. 2014).

The research was conducted as part of an interdisciplinary project, including a fine-scale flood model, a geospatial platform for displaying and exploring the results, and focus groups with community stakeholders (see appendix for list of participants). The focus group discussions were semistructured, meaning they had a set of predefined questions but also allowed space for new insights to emerge through impromptu follow-ups. The interviews were recorded and automatically transcribed.

One theme that emerged from the focus groups was that Angelenos tend to view flooding as a non-issue, partly because many believe California is flat and excess water from high precipitation or sea level rise will not have much of an impact. In addition, some think their properties are already protected by the presence of existing levees or flood channels, while others see a flood as an inevitability that can never be fully avoided or prepared for.

The findings also highlight the need for increased engagement between communities and public agencies to discuss local flooding risks. This is particularly critical for issues with changing outcomes, such as floods, where collaboration with local stakeholders can increase the likelihood that planned interventions will be effective and relevant. Moreover, engaging with community members during the development of risk assessment and resilience plans can help ensure that the needs and concerns of affected communities are heard and addressed in the design process (Lara et al. 2012; Lawrence et al. 2014).