Partial Flood Defenses Shift Risks and Amplify Inequality in Core–Periphery City

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, along with depth–damage curves and demographic data, we find that partial levee construction in Surat, India, lowers citywide flood losses by rupee31.24 billion (US$380 million) in core urban wards and rupee10.34 billion (US$125 million) in suburban neighborhoods. However, damage and exposure both become more inequitable, with the Gini index (0 = perfect equality, 1 = maximum inequality) rising by about 20% for damage (0.55 to 0.66) and 26% for exposure (0.31 to 0.39). We also introduce floodstripes and a Protection-Induced Time Shift (PITS) to capture both spatial and temporal changes, showing 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 addressing both dimensions of partial flood protection, ensuring that benefits for some do not escalate vulnerabilities for others.