Socio-spatial drivers of thermal environment evolution in East African informal settlements based on multi-temporal LCZ analysis of major metropolises

Unplanned urbanization in Sub‑Saharan Africa (SSA) is producing vast informal settlements that amplify surface urban heat island (SUHI) intensity, yet the mechanisms driving heat exposure in informal settlements remain poorly understood. This study presents the first standardized, multi‑temporal Local Climate Zone (LCZ) analysis of Kampala, Nairobi, and Dar es Salaam (2014–2024), introducing a validated LCZ 37 subclass to capture compact‑lightweight informal morphology, operationally defined based on physical surface properties correlated with known slum areas. Urban form followed a two‑stage trajectory: horizontal expansion (2014–2020) succeeded by spatial consolidation (2020–2024). Within each city’s seasonal baseline, informal SUHI intensity increased over the decade: Kampala + 1.22 °C, Dar es Salaam + 2.48 °C, and Nairobi + 3.65 °C, making Nairobi the most rapidly warming informal environment within its own seasonal context. A driver regime shift was detected: two‑dimensional impervious cover (NDISI) dominated during expansion, while three‑dimensional building density (NDBBI) became the primary driver during consolidation, particularly in inland cities. Geographically Weighted Regression (GWR) exposed spatially concentrated heat‑amplification mechanisms, including collapse of surface moisture cooling in Kampala and co‑location of built density with economic activity in Nairobi, invisible to global models. These divergent trajectories argue against generic mitigation prescriptions, underscoring the need for LCZ‑informed, context‑sensitive strategies (i.e., cool‑roof retrofits in Kampala/Dar es Salaam; targeted green infrastructure in Nairobi) to achieve equitable heat resilience.