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

• Urban green spaces’ CE tends to be bigger in drier cities. • AT dominates CE in most cities while WS dominates CE in cities with larger WS. • CE responses oppositely to meteorological variables after Fc turning point. Increasing land surface temperature (LST) is one of the concerns of urbanization consequences. Urban green spaces are gaining more 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 vegetation cover fraction (Fc), has received less attention. CE can be influenced by climate background, but the impacts are still 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 ordered generally by arid (Cairo, 7.51, Kano, 6.81), temperate (Cape town, 9.21, Durban, 5.95, 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 larger wind speed, wind speed influenced more. 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 after it. The clarification of climatic impacts and Fc turning point provides climate-tailored guidelines for urban green space planning.