Urban vegetation cooling potential during heatwaves depends on background climate

The capacity of vegetation to mitigate excessive urban heat has been well documented. However, the cooling potential provided by urban vegetation during heatwaves is less known even though heatwaves have been projected to be more severe with climate change. Across 24 global metropolises, we combine 30 m resolution satellite observations with a theoretical leaf energy balance model to quantify the change of the leaf-to-air temperature difference and stomatal conductance during heatwaves from 2000 to 2020. We found the responses of urban vegetation to heatwaves differ significantly across cities and they are mediated by climate forcing and human management. During heatwaves, vegetation in Mediterranean and midlatitude-humid cities shows a significant decrease in cooling potential in most cases due to large stomatal closures, while vegetation in arid cities shows a cooling enhancement with an unmodified stomatal opening likely in response to intense irrigation. In comparison, the cooling potential of vegetation in high-latitude humid cities does not show significant changes. These responses have implications for future urban vegetation management strategies and urban planning.