Opposite climate impacts on urban green spaces? cooling efficiency around their coverage change thresholds in major African cities

Increasing land surface temperature (LST) is one of the concerns associated with urbanization. Urban green spaces are gaining attention given its well-documented heat mitigation effects. However, the cooling efficiency (CE) of green spaces, which can be quantified as the negative ratio of LST changes to per unit change of vege-tation cover fraction (Fc), has received less attention. CE can be influenced by climate background, but the impacts remain unclear. Here we selected LST and meteorological data across 7 days of heatwaves in six major African cities and analyzed the CE and its response to meteorological variables. The mean CE generally ordered by arid (Cairo, 7.51 and Kano, 6.81), temperate (Cape Town, 9.21, Durban, 5.95 and Nairobi, 5.88), and tropical (Accra, 3.26) cities. CE showed a positive response to temperature dew point difference and wind speed. Air temperature dominated the CE in most cities, but in cities with higher wind speeds, wind speed exerted greater influences. CE in all cities experienced significant changes when the Fc reached a specific value (Fc turning point) and CE's response to meteorological variables also reversed following the threshold. The clarification of climatic impacts and Fc turning points provides climate-tailored recommendations for urban green space planning.