Height-aware and protection-informed flood assessment shifts global urban risk distribution

Abstract Floods pose a significant global threat, causing widespread human and economic losses. However, current flood risk assessments frequently rely on simplified assumptions, such as uniform flood depth-damage relationships and country-level protection standards, that neglect crucial factors like building height and the regional variation in flood protection capacity. These assumptions limit how structural exposure and protection effectiveness can be represented. Moreover, most assessments operate at coarse spatial resolutions, overlooking the fine-grained variability and heterogeneity at city and neighborhood scales. This study introduces a comprehensive framework that integrates flood depth, building height, and protection standards across multiple scales, aggregating analyses from individual pixels to functional urban areas, countries, and world regions. Building height enters the framework through the inundation ratio, a height-normalized index of potential structural exposure. Moving from a depth-only to a height-aware indicator raises a region’s share of global assessed risk by about 40% where buildings are short (e.g., Africa) and lowers it by about 20% where buildings are tall (e.g., Central and South America). Applying regional protection standards further reshapes the landscape: the combined share of Europe, North America, Oceania, and East Asia falls from 37 to 14%, whereas the share of South Asia, Africa, and Central America rises from 29 to 47%. Conventional assessments mask the concentration of flood risk in regions with the lowest modeled protection standards. The findings provide actionable insights for guiding targeted interventions and mitigating flood impacts in vulnerable areas.