Exposure Inequality and the Evolution of Social Vulnerability to Urban Flooding under Multiple Rainfall Scenarios

To systematically investigate exposure differences among social groups to urban flooding, this study focuses on the central urban area of Shanghai. Using the TELEMAC-2D two-dimensional hydrodynamic model, this study simulate flooding processes under rainfall events with return periods of 20, 50, and 100 years. We extract maximum water depth and flow velocity and combine these parameters with flood hazard indicators to delineate flood risk zones and examine the spatial expansion of flooding under different scenarios. Then 100-m resolution population grid data and residential property price information are integrated to quantitatively assess flood exposure from three perspectives: total population, the elderly population aged 65 and above, and socio-economic groups at different income levels. This analysis emphasizes the non-uniform distribution of social group exposure under extreme rainfall conditions. Furthermore, we construct an integrated vulnerability index by applying the entropy weight method to flood hazard intensity, elderly population exposure, and economic vulnerability. The index characterizes the spatial pattern of vulnerability risk and its dynamic evolution in response to increasing rainfall intensity. The results indicate that both the extent of high-risk areas and the size of the exposed population increase markedly with longer rainfall return periods. Elderly populations exhibit a pronounced amplification of exposure within high-risk zones. Under certain flooding scenarios, areas with relatively high economic status still display significant clustering of vulnerability risk. Overall, the findings demonstrate that urban flood risk is strongly differentiated across social groups. These results provide scientific support for equity-oriented urban flood risk management and targeted protection strategies for vulnerable populations.