Mapping global future coastal inundation risk and demographic vulnerability using multi-sensor remote sensing data and socioeconomic scenarios

Sea level rise, land subsidence and increasing wave heights will exacerbate inundation risk in future in coastal areas, which are usually densely populated and economically developed. However, the specific distribution of populations at inundation risk and the contribution rates of inundation risk impact factors remain unclear. To address these gaps, we first estimated the numbers and distribution of inundated coastal populations in 2050 and 2100 under three Shared Socioeconomic Pathways (SSPs), including SSP126, SSP245 and SSP585, which represent low-, medium-, and high-emission trajectories, respectively. Second, we analyzed the impacts of inundation risk on coastal populations across different income groups under the three scenarios. Third, we quantified the contribution of inundation risk factors for three scenarios in 2050 and 2100 by using random forest model. Finally, we discuss the impact of inundation risk on the socioeconomic and ecosystem of coastal areas. Our findings indicate that the global population at risk of inundation will exceed 543.6 million by 2050 and 568.7 million by 2100. Inundation risk increases with rising temperatures, with East and Southeast Asia accounting for two-thirds of the affected population. The results show that the populations at inundation risk with lower middle or low income will reach 277.4 million, 284.5 million, and 300.4 million by 2050 under SSP126, SSP245 and SSP585, respectively. These numbers are projected increase to 328 million, 356.7 million and 407.3 million in 2100, amplifying climate-related inequalities. We find that people with lower middle or low income at inundation risk are primarily concentrated in Southeast Asia, South Asia and Africa. Additionally, we identified regional differences in the dominant drivers of inundation risk. Land subsidence plays a primary role in the low latitude countries of Southeast Asia and South Asia, including Vietnam, Bangladesh, the Philippines and Indonesia. In contrast, wave height is the dominant factor in countries like the Netherlands, Egypt, China, and the United States, with its influence increasing as temperatures rise. Inundation can trigger many factors that threaten social stability in a coastal country with low income and severely damage the ecological system of coastal areas. These results underscore the urgent need for targeted climate adaptation strategies, particularly in low-income coastal regions. These findings enhance understanding of inundation risk drivers and provide scientific support for hazard mitigation and coastal ecosystem protection.