Mapping global floodplain development disparities highlights drivers underlying intensifying flood losses

Floodplains attract disproportionate concentrations of population and economic activity globally, yet the systemic flood risks emerging from this uneven development remain poorly characterized. Through a global analysis spanning 2000-2020, we quantify floodplain development patterns and associated flood losses across nations with varying income levels and flood protection capacities. Our results reveal that floodplains have experienced faster growth than non-floodplains in both population density and GDP density. These trends diverge sharply by income and protection levels: floodplain population density growth rates in low- and lower-middle-income countries outpaced those in high-income nations by factors of 2.33 and 7.58, respectively. Similarly, due to levee effect, regions with flood protection capacity of 100 years or more experienced GDP density growth that was 4.51 times higher than in regions with less than 10-year protection. The heightened sensitivity of flood losses to socio-economic growth stems from uneven floodplain development. This creates a divergent risk pattern: wealthier, well-protected regions accumulate greater economic assets at risk, whereas poorer, under-protected areas face the compounded burden of exposure to both population and GDP risks. Our findings highlight the urgent need for flood risk adaptation strategies that explicitly consider and address underlying floodplain socio-economic inequalities in exposure and protection.