Urban flood risk and green infrastructure: Who is exposed to risk and who benefits from investment? A case study of three U.S. Cities

Abstract

Pluvial flooding is a serious hazard in inland U.S. cities. City managers and communities are increasingly interested in reducing their pluvial flood risk through the development of green infrastructure (GI) features. This research explores the relationship between pluvial flood exposure and GI placement in three inland cities–Atlanta, Phoenix, and Portland–and analyzes the variation of sociodemographic variables in census block groups (CBG) located in pluvial flood zones. Using the Arc-Malstrøm method, we estimated areas of pluvial flooding in the CBGs of our selected cities by relating pluvial flood area to the density of GI in CBGs and assigning CBGs one of four classifications: i) managed (large flood area, abundant GI), ii) prepared (small flood area, abundant GI), iii) vulnerable (large flood area, scarce GI), and iv) least concern (small flood area, scarce GI). Then, using the historical GI data, we examined the proportionality of GI investment over time to pluvial flood area. We found relationships between GI density, flood area, ethnic and racial minority populations, age, educational attainment, and median household incomes that indicated inequalities and potential discrimination in flood risk management, but also some evidence of equitable and appropriate management given differences in flood risk, especially in Phoenix and Portland. In Atlanta, newer GI installation prioritized white and wealthy neighborhoods where relatively higher flood risk exists (less equitable). Our classification framework may assist city flood risk managers to distribute GI more equitably according to equitability and need.