Cooling effect of urban greenery: A bibliometric analysis

The mechanism and effectiveness of urban greenery in mitigating urban heat islands, regulating microclimate, and enhancing thermal comfort has been extensively studied during the last decades. While sporadic empirical evidence has been generated, the trends and patterns of existing scholarship pertinent to urban greenery's cooling effect have been rarely summarized and synthesized. To bridge this knowledge gap, the present paper systematically reviewed 310 relevant publications in the Web of Science database (1998-2022) and conducted a bibliometric analysis to depict a comprehensive profile of urban greenery's cooling effect, focusing on global research trends, prevalent research topics, and future prospects. Our analytical results reveal (1) a steady increase in publications, active journals, and knowledge-generating institutions since 2008 that might be attributed to the free accessibility of diverse remote sensing data; (2) a significant increasing trend of transdisciplinarity and interdisciplinarity, expanding from Environmental Science and Ecology to various subjects such as Engineering, Remote Sensing, Construction & Building Technology, Urban Forestry, and Urban Studies; (3) four influential publication outlets including Urban Forestry & Urban Greening, Science of the Total Environment; Building and Environment, and Sustainable Cities and Society; (4) core research themes focusing on the association of urban greenery's biophysical characteristics with cognate cooling effect, urban heat island mitigation, and land surface temperature; and (5) several new research themes that have not yet well-developed in the extant literature, including the integration of various analytical approaches to up-scale empirical studies from micro-scale to mesoand global scales, extending urban greening-thermal comfort to public health and social thermal justice, and coupling urban greenery's cooling effect with other environmental/ecological benefits to inform the design of urban greenery for biodiverse, climate-resilient and sustainable cities. Findings of this synthetic review offer a reference for the research focusing on urban greenery's cooling effect, and provide clear direction for further development of cognate scholarship that is urgently needed facing more frequent urban climate extremes along with global warming.