Impacts of urbanization on temperatures and agricultural drought in Africa based on Urban Heat Drought Index from 2000 to 2023

Abstract

Rapid urbanization in Africa, particularly in Greater Cairo, Egypt, and Nairobi, Kenya, has significantly contributed to environmental change through increased Land Surface Temperature (LST) and the intensification of the urban heat island (UHI) effect. This study assesses the impact of urbanization on LST, UHI, and drought from 2000 to 2023. The Urban Heat Drought Index (UHDI) is a novel PCA-based metric that integrates urban heat indicators (LST, UHI, NDBI) with vegetation and moisture indices (NDVI, NDII), using Landsat data to capture urban-induced drought stress often overlooked by conventional indices. Between 2000 and 2023, Greater Cairo and Nairobi experienced LST increases with 9.0 °C and 7.5 °C, respectively, corresponding to urban expansion rates of 550% and 78%, which highlights the strong link between built-up growth and thermal intensification. The UHDI exhibited high correlations with SPI-1 (0.88 and 0.87), SPEI-3 (0.77–0.88), and VHI (0.98), reflecting deteriorating drought conditions and declining vegetation health due to UHI impacts. Validation with past drought events supported UHDI's reliability in capturing urban-induced drought stress. Drought severity maps revealed gradients ranging from mild to extreme drought, emphasizing the role of urbanization and rising temperatures in the intensification of environmental stress. UHDI integration is vital for sustainable, climate-resilient urban planning.