Fine-scale assessment of inequities in inland flood vulnerability

Every year, river floods disrupt millions of lives across the world, impacting individual livelihoods and testing the resilience of entire communities, with ripple effects through national economies. Not all households and communities are equally threatened by floods, but disparities in flood vulnerability within and between communities remain poorly quantified owing to coarse census data and inconsistency in official flood hazard maps. Here we address this gap by leveraging state-of-the-art flood hazard estimates and novel, fine-scale demographic information. We examine whether households experience unequal vulnerability to inland flooding based on their race and ethnicity in Washington State, U.S.A. Focusing on individual land parcels, we show that 9% of the population in the state lives in a flood zone, 16% of which are Latinx, even though Latinx residents make up only 8% of the overall population. Beyond disparities in exposure, we found that communities also differ in their vulnerability to floods. We demonstrate that using finer-grain data and improved flood hazard maps leads to starker estimates of total flood exposure and racial/ethnic inequities than using official data and conventional methods. Our results provide key information to advocate for and guide actions to mitigate racial and ethnic inequities in flood vulnerability.