Urban Morphology and Thermal Exposure in Senegal’s Major Cities

Accelerating urbanization across West Africa is intensifying urban heat islands (UHIs), yet the national-scale thermal consequences remain largely unquantified. This study presents an integrated characterization of urban morphology and thermal exposure across eight major Senegalese cities Dakar, Touba, Thiès, Kaolack, Mbour, Rufisque, Saint-Louis, and Ziguinchor over a 24-year analytical window (2000–2024). Four complementary approaches were combined: (i) a high-resolution Local Climate Zone (LCZ) classification produced with GeoClimate v1.0 from OpenStreetMap data following the Stewart and Oke (2012) standard; (ii) a multi-temporal land use/land cover (LULC) analysis (2000–2020) integrating MODIS MCD12Q1 and GHSL GHS-BUILT-S products; (iii) spatiotemporal land surface temperature (LST) retrieval from the Landsat archive processed on Google Earth Engine (GEE); and (iv) a 2024 heat-stress map using a Random Forest supervised classifier combining LST, NDVI, and NDBI (overall accuracy 98.1%, Kappa 0.936). Built-up surfaces expanded by approximately 357,000 ha over 2000–2020 (+ 170%), with 61.1% converted from savanna and 37.3% from agricultural land. This expansion produced a national LST increase of + 1.2°C and urban surface temperatures reaching 49.0°C in Touba. The LCZ–heat stress cross-analysis (Kruskal–Wallis H = 143.7, p < 0.001) reveals a robust morpho-thermal gradient: compact built-up zones (LCZ 2–3) exhibit mean stress scores (S̄) two to three times higher than those of natural zones. This gradient is further modulated by a systematic macroclimatic offset of 0.5–0.8 S̄ units between coastal and Sahelian inland cities, irrespective of LCZ class. Building surface fraction (BSF, ρ = 0.74) and pervious surface fraction (PERVF, ρ = −0.71) emerge as the primary morphological determinants of thermal exposure. A key original finding is the LCZ A paradox: dense trees provide effective cooling in humid Ziguinchor (S̄ = 1.1) but remain thermally near-neutral in arid Touba (S̄ = 2.7), demonstrating that canopy density and soil water availability are the critical conditions governing the cooling efficacy of urban greening in dryland contexts. These findings provide the first national LCZ baseline for Senegal and an open-source methodological framework transferable to Sahelian cities across West Africa. They also constitute an operational mapping foundation for mainstreaming UHI mitigation into the revision of Senegal’s Nationally Determined Contribution (NDC) and the monitoring of SDGs 11 and 13.