Landscape signatures of surface heat susceptibility in West African coastal cities: A harmonised four-city assessment

Abstract Rapid urbanisation is reshaping blue-green and built-up landscapes across West African coastal cities, yet comparable evidence on associated surface heating remains limited. This study assessed surface heat susceptibility in Accra, Lagos, Abidjan and Freetown during 2024. Sentinel-2 imagery and Random Forest classification were used to map land use and land cover, while Landsat 8 and 9 data provided land surface temperature (LST), Normalised Difference Vegetation Index (NDVI) and Normalised Difference Built-up Index (NDBI). A Surface Heat Risk Index (SHRI) integrated equally weighted, pooled-normalised LST, NDBI and inverse NDVI using common classification thresholds. Built-up and bare surfaces were consistently warmer than vegetation and water. LST was negatively associated with NDVI and positively associated with NDBI, confirming the contrasting thermal effects of vegetation and built-up intensity. Moderate SHRI dominated Accra (75.70%) and Freetown (84.89%), whereas low SHRI dominated Lagos (62.80%) and Abidjan (73.16%). Freetown recorded the largest high-class proportion, but this represented only 0.134% of its valid area; the other cities each recorded less than 0.002%, and no measurable area was classified as very high. The framework supports comparable screening of heat-sensitive landscapes and can inform urban greening, blue-green infrastructure protection and impervious-surface management. Because population exposure and socioeconomic vulnerability were not included, the SHRI represents biophysical surface heat susceptibility rather than direct human heat risk.