Surface urban heat island of metropolitan Italian cities: tree cover and impervious surface influences - Supplementary materials

Based on the 2018 population census, around 70% of the Italian population lives in urban areas and just over 30% lives in the 10 metropolitan cities of the Italian peninsula. The knowledge of processes that regulate the urban microclimate is a priority in order to design acceptable thermal environments for urban living spaces. Studies investigating the right trade-off between the amount of important land surface temperature (LST) predictors, such as impervious and vegetated surfaces, are strongly encouraged. These LST-predictors strongly influence the urban landscape mosaic, also changing microclimate conditions and exacerbating the surface urban heat island (SUHI) phenomenon. The aim of this study was to lead an investigation of the summer daytime SUHI phenomenon and the role played by impervious and tree cover surfaces in the 10 peninsular metropolitan cities located in several Italian regions. Daytime summer LST values were assessed by using MODIS data referred to the months of June, July and August from 2016 to 2018. High spatial resolution (10 m) of impervious surface and tree cover layers were calculated based on open-data developed in this study by the Italian National Institute for Environmental Protection and Research. A novel informative urban surface landscape layer was implemented combining impervious surfaces and tree cover densities and its mapping for metropolitan cities were provided. The summer daytime SUHI significantly increased especially in inland cities by increasing the extension of the areas characterized by low tree cover densities in the metropolitan core (or decreasing the areas with low tree cover densities outside the metropolitan core), further rising its intensity when the impervious density grew. Increased impervious surfaces combined with low tree cover densities represented the main driving process to increase the summer daytime SUHI intensity in most studied cities. These findings are useful to identify summer daytime LST Hot-Spots and to implement the most efficient urban-heat-island mitigation strategies in order to safeguard the vulnerable urban environment and enhance the quality of life of the population.