Socioeconomic predictors of vulnerability to flood-induced displacement.

Floods displace an average of 12 million people every year, and are responsible for 54% of all disaster-induced displacements. Displacement risk scales with the vulnerability of exposed populations, but this vulnerability is poorly understood at a global scale. Here we show that measures of human development and rural areas explain more of the variance of displacement vulnerability than income levels measured by gross domestic product. We combine global flood and displacement data to estimate vulnerability, as the ratio of displacement to exposure, for over 300 historical flood events. We find that this vulnerability varies by several orders of magnitude both between and within countries. A random forest regression shows that infant mortality rate and population density are among the most important predictors of displacement vulnerability at national level and within countries, respectively, highlighting the vulnerability of low-income and marginalized populations and of rural communities. Our results indicate that, rather than relying on overall economic development alone, targeted investments are needed to improve living conditions and coping capacities for the most vulnerable groups, particularly outside of large cities, and to prepare for increasing flood hazards due to climate change.