Heterogeneity in Flood Hazard Exposure in 363 Latin American Cities.

Flooding is among the costliest natural disasters worldwide, yet how riverine flood hazard is distributed within cities remains poorly quantified, particularly across socially vulnerable population groups. Climate change is intensifying flood magnitude, duration, and frequency, raising concerns that existing inequalities in flood exposure will widen. Using data from the multi-country Salud Urbana en América Latina project, we assess disparities in riverine flood hazard among residents of 363 cities across 9 Latin American countries. We develop 2 city-level indicators, the exposure deviation index (EDI) and the Giniflood index, to quantify disproportionality and spatial unevenness in populations residing in riverine flood-prone areas. Across 297.9 million urban residents, 6.9% are exposed to floods with an annual exceedance probability of 0.2% (500-y events), and children (<10 y) are more exposed than others. EDI values are generally small and slightly negative at the country level, indicating that populations are not systematically overrepresented or substantially underrepresented in hazard areas relative to land share of flood-prone area extent, although substantial variation exists across cities and countries. In contrast, Giniflood values are consistently high, indicating that exposed populations are strongly concentrated within a limited number of spatial units. Inland cities at higher elevations tend to exhibit greater disproportionality and unevenness, while at the regional scale, differences across age and education subgroups are limited. These findings provide transferable indicators for a relative assessment of flood hazard heterogeneity and underscore the need for equitable land use, housing policy, and infrastructure planning to advance climate resilience and environmental justice.