Land Surface Temperature patterns in Nairobi, Kenya : A study of Inequality of Heat Exposure

Sammanfattning

Urban heat is a growing challenge especially in rapid growing cities, especially where dense buildings, limited vegetation and socio-economic vulnerability coincide. This study examines the patterns in Land Surface Temperature (LST) in Nairobi County, Kenya. The purpose is to analyse how LST varies between different years, seasons and different parts of the city. The study is based on Landsat 8 OLI/TIRS-data from 2016, 2020 and 2024. With help from the satellite images LST, Normalized Difference Vegetation Index (NDVI), Normalized Difference Built-up Index (NDBI) and Urban Index (UI) were calculated. Hotspot zones were identified with help of thresholds, based on mean values and standard deviations for LST. Surface Urban Heat Islands (SUHI) were analysed through a comparison between Nairobi County, Karura Forest, and parts of Kiambu County. Furthermore, different neighbourhoods were compared with each other based on LST-patterns, vegetation cover, building structure, population density and relative wealth. The results show that LST is not evenly distributed over Nairobi County. Higher LST values were primarily found in the central, southern and eastern parts of the city. Lower LST values were primarily found in the west and northwest part which had more vegetation and less building intensity. The SUHI-analysis showed that Nairobi County had higher LST values than Karura Forest and the reference area of Kiambu County. The hotspot analysis showed that repeated hotspots were concentrated to industrial areas and densely built residential areas. Those areas were primarily concentrated to the central parts of the city. The comparison between different neighbourhoods showed that areas with weaker socio-economic conditions had higher LST values and less vegetation. Instead, they had more buildings and impervious surfaces and higher population density. This study shows that LST-patterns in Nairobi are shaped by the interaction between vegetation, built-up areas, land use and socio-economic conditions. The results show that green infrastructure and reduced share of impervious surfaces can be important strategies to reduce urban heat effects, especially in densely populated and socio-economic vulnerable areas.