Partial flood defenses shift risks and amplify inequality in a core-periphery city

Abstract

Cities worldwide often rely on partial structural defenses to mitigate intensifying flood hazards. Although large-scale analyses suggest that partial levee coverage can reduce overall damage, its spatiotemporal effects remain understudied, particularly in cities of the Global South. Using a hydrodynamic model forced by extreme discharges (100-year return period flood event), along with depth–damage curves and demographic data, we find that partial levee construction in Surat, India, lowers citywide flood losses by ₹31.24 billion (US$380 million) in core urban wards and by ₹10.34 billion (US$125 million) in suburban neighborhoods. However, both damage and exposure become more inequitable, with the Gini index (0 = perfect equality, 1 = maximum inequality) rising by 20% for damage (0.55 to 0.66) and by about 26% for exposure (0.31 to 0.39). We introduced flood stripes and a protection-induced time shift to capture both spatial and temporal changes, finding that certain near-river wards can remain flood-free for up to 12 hours longer, whereas some downstream areas flood up to 7 hours earlier under partial levee coverage. These findings underscore the need for integrated strategies that address both dimensions of partial flood protection, ensuring that benefits for some do not escalate vulnerabilities for others.