Uneven heat exposure in Global South megacities: a comparative analysis of informal settlements in São Paulo and Delhi

Abstract Rapid urbanization and climate change are intensifying urban heat islands and extreme heat events, posing growing health risks, particularly for vulnerable populations. This study investigates disparities in surface heat exposure across informal settlements in two Global South megacities, São Paulo (Brazil) and Delhi (India), during peak summer conditions. Combining Landsat 8-derived Land Surface Temperature (LST) with indicators of vegetation (NDVI), built-up density (NDBI), and topography, the study adopts a comparative and multi-scalar approach to analyse how urban morphology and land cover shape intra-urban thermal patterns. Results indicate that informal settlements are consistently more heat-exposed than formal areas in both cities, although the spatial configuration of exposure differs markedly between the two cities. In São Paulo, favelas emerge as localized heat hotspots (mean LST: 40.6 °C) embedded within a heterogeneous thermal landscape, with high variability (ΔLST = 12.2 °C). In Delhi, slums are situated within a more uniformly overheated urban fabric, presenting higher average temperatures (≈ 44.8 °C) but lower variability (ΔLST ≈ 9.3 °C). Across both contexts, vegetation is consistently associated with lower surface temperatures, while built-up density intensifies heat exposure; population density shows no significant relationship with LST. The findings highlight urban morphology as a key determinant of heat exposure and reinforce thermal risk as an important dimension of socio-spatial inequality in the Global South. The study provides insights for applied urban planning and climate adaptation strategies, emphasizing the need for morphology-informed and context-sensitive interventions in informal settlements.