## 1 Introduction  
Cities all over the world are experiencing very fast growth and changes due to the current rapid urbanization. This is the reason why the United Nations included Goal 11: Make cities inclusive, safe,resilient and sustainable within the 17 Sustainable Development Goals (SDGs) issued in 2015. A key issue after the definition of the SDGs is the monitoring of their progress; with regard to SDG 11, there is a need for well globally-defined, easy computable and comparable indicators, representing different aspects of city conditions, obviously including the Land Cover (LC) changes and the urban climate with its most distinct feature, the Urban Heat Island (UHI) [1; 2]. Specifically, the term UHI refers to the mesoscale phenomenon associated with higher atmospheric and surface temperatures occurring in urban environments compared to in the surrounding rural areas due to urbanization [3]. It is characterized by a large expanse of non-evaporating impervious materials covering a majority of urban areas with a consequent increase in sensible heat flux at the expense of latent heat flux. Therefore, the UHI and its spatio-temporal evolution are connected to the LC changes, mainly to the transformation from non-urban to urban LC. Globally, urban footprints only account for approximately 2% of the planetary surface [4]. It was well documented that with the rapid urbanization and population growth, the increase in built-up land and the natural land replacement with artificial buildings has altered the surface energy budgets and the hydrological cycle and may affect local and regional climate by changing the physical properties of the Earth's surface [5]. Over the past decades, worldwide urbanization and climate change have been two interconnected processes describing the role of human activities in altering and modifying the climate system, which, in turn, may result in uncertain feedback for human welfare. The UHI effects are exacerbated by the anthropogenic heat generated by traffic, industry and domestic heating, influencing the local climate through the compact mass of buildings that affect the balances of momentum, heat and moisture. The higher temperatures in UHIs increase air conditioning demands [6; 7], with a retrofit effect of increasing the outdoor temperature even more, and may modify precipitation patterns. As a result, the magnitude and pattern of UHI effects have been major concerns of many urban climatology studies [8]. The UHI has been a well-known phenomenon since the XIX Century, and it has been studied for many decades; an excellent review of the state-of-the-art (measurements, models, result interpretations) is given in [9], which addresses the four different aspects of UHI, including the Surface Urban Heat Island (SUHI) besides others (canopy urban heat island, boundary urban heat island and subsurface urban heat island). Traditionally, the UHI is investigated using ground-based in situ measurements of air temperature acquired by automatic weather stations (e.g., see [10]). Air temperature measurements allow one indeed to characterize the fine spatial and temporal variations of the UHI, and they are suitable for studying the impacts of local indicators of urbanization (e.g., sky view factor, floor area ratio) and climate factors (e.g., wind, cloud) contributing to the phenomenon [11; 12; 13; 14]. Nonetheless, the urban meteorological networks are not always as complete as could be desired, and frequently, their stations are not uniformly distributed within the territory of the investigated cities. Consequently, large zones may remain without coverage, and it is not possible to analyze the different spatial pattern. Another possible approach is to investigate the UHI phenomenon through numerical simulations. For instance, ongoing analyses about the UHI at the mesoscale level investigate the effectiveness of superficial properties by using the Weather Research and Forecasting (WRF) mesoscale simulation [15; 16].