Multidimensional vulnerabilities of informal settlements in the Urban South

Informal settlements are widespread and rapidly growing, often associated with high vulnerabilities. However, global-scale understanding on their spatial distribution and complexity of vulnerability is limited. Here, we delineate the informal settlements across a sample of 1,914 cities of the Global South by integrating Sentinel-2 imagery with deep learning models, and we explore the heterogeneity of vulnerability using Urban Informal Settlement Vulnerability Index that encompasses living conditions, social infrastructure, and environmental risk. We found that Urban Informal Settlements cover 12.94 ± 2.52% of their total urban areas (approximately 34.04 × 10³ km²), especially in sub-Saharan Africa, South Asia, and Middle Asia. Sub-Saharan African cities have the highest vulnerability of informal settlements, with 31.75 ± 6.20% of total urban areas being occupied by informal settlements, while East Asian cities exhibit relatively low vulnerability across all dimensions. We also find that urban informal settlements with high environmental exposure are widespread in the Global South, and there is a significantly polarized distribution between "low" and "high" vulnerability categories. The findings highlight the disparate distribution of multidimensional vulnerability in informal settlements across the Urban South, providing a comparative evidence base for further local assessment and context-specific policy discussions related to SDG 11.