Global urban greening and its implication for urban heat mitigation

Urban vegetation provides essential ecosystem services and benefits to support biodiversity and human well-being in urban areas. However, the dynamic trends, driving factors, and their implications to urban heat mitigation at the global scale remain largely unclear. Here, we used a high-resolution enhanced vegetation index (EVI) dataset to examine the vegetation dynamics in 11,235 urban areas worldwide, identify the driving factors behind its changes, and estimate the potential urban heat mitigation benefits of these changes. We found that 40.75% urban areas (1.51 Mha) evidenced a greening trend (showing increasing EVI), in contrast to 49.60% urban areas showing browning (decreasing EVI). Notably, urban centers in both developed and developing countries contribute to this greening trend. We, nevertheless, found significant spatial disparities in this greening trend, with cities in the Global North showing higher greening ratios than those in the Global South. The driving factors of urban vegetation change trend lead to significant differentiation in and around urban areas. The rapid increase in urbanization intensity and the negative effects of nitrogen deposition are the dominant factors leading to vegetation browning in urban peripheries. However, nitrogen deposition and urbanization intensity have shown positive effects on vegetation greening within urban centers. Crucially, compared to areas with vegetation browning or no significant change, vegetation greening areas have a more significant cooling effect, potentially mitigating the urban heat island effect, especially during summer daytime. Our findings highlight the importance of enhancing urban vegetation greening to promote equitable urban development and ensure effective climate change mitigation.