<p>Rapid urbanization is leading to the expansion of human settlements in flood-prone areas, and the impact is not uniform across different communities. Few studies have comprehensively investigated the flood exposure faced by vulnerable communities in the Global South, where pervasive slums present a major challenge to inclusive urban planning and flood management. Here, combining advanced machine learning techniques and publicly available satellite images, we identify hot spots of urban slum populations in floodplains in the Global South and examine their settlement patterns. We find that approximately one in three people living in slums in the Global South resides in a floodplain. Slum dwellers are 32% more likely to settle in floodplains compared with residents in adequate housing. The concentration of slum populations is particularly high in areas that have experienced severe floods. These data-driven insights highlight the disproportionate flood exposure faced by slum dwellers in the Global South and underscore the need for just and equitable flood adaptation management.</p>