The cooling impact of urban greening: A systematic review of methodologies and data sources

Urban greening is a practical adaptation to improve the liveability of a city by providing urban cooling. This paper systematically evaluates the existing literature to understand the methodologies and associated data sources for determining the cooling effect provided by urban greening. A bibliometric analysis, including research focus parallelship network analysis and keyword co-occurrence network analysis using Gephi and BibExcel, was first performed on 156 articles to identify the main resulting research themes in cooling provided by UGAs. Subsequently, 72 of these were selected to extract more information, such as the focus, the measured parameters, the methods, and tools employed to measure cooling parameters, and the studies` scales. The bibliometric analysis identified three emerging themes: (1) on-site measurement to directly collect meteorological data, (2) remote sensing techniques used to calculate cooling indices such as cooling distance and intensity, and (3) estimation and prediction of urban temperature through modelling. The results showed that the field measurement was used in studies that have smaller spatial scale (i.e. those that examined a small number of parks). Remote sensing techniques were used to investigate larger spatial areas in which cooling indices were estimated through measurement of land surface temperature rather than the air temperature. It is also revealed that some green space and meteorological parameters have received more attention. The findings of this research will enable green space designers and urban planners to become aware of the differences between various methods for calculating cooling and the importance of various parameters. However, future research should include a mix of data acquisition, covering all urban and greenery features to quantify urban cooling, and economic and social benefits of urban greening development. A novel measurement design is proposed through which a more accurate estimation of the cooling effect of green spaces can be obtained.