## Materials
### Data Collection
#### 2.2.2 Air Temperature Observations  
Time series of environmental and weather observations are traditionally collected and distributed by public authorities with fewer restrictions. In Italy, official environmental monitoring is accomplished by the Regional Agency for Environmental Protection (ARPA, _Agenzia Regionale per la Protezione dell'Ambiente_) through its sensor networks located in all the 20 administrative regions. Time series \begin{table}
\begin{tabular}{l c c} \hline \hline \multirow{2}{*}{**Satellite**} & \multicolumn{2}{c}{**Acquisition Date and Time**} \\ \cline{2-3}  & **Non-Vegetative** & **Vegetative** \\ \hline Landsat 8 & 18-03-2016 10:10 a.m. & 22-06-2016 10:10 a.m. \\ Sentinel-2 & 13-01-2016 10:20 a.m. & 22-05-2016 10:20 a.m. \\ RapidEye & 18-03-2016 11:14 a.m. & 22-06-2016 10:46 a.m. \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Acquisition date and time for satellite images. Time is given in Greenwich Mean Time (GMT). can be requested by any user through the ARPA data download platform. Data is provided under a custom open license with quality standard certification as requested by the national law. For this study, additional weather stations are considered in order to increase the spatial coverage of temperature observations over the study area. This is due to the need of investigating the correlation between temperature observations and LCZ at a very local scale, i.e., taking into account the likely point-wise nature of the two phenomena and their possible cause-effect relationship (see Section 3). The additional observations are collected from the Weather Underground (WU) platform [36]. This is an Internet service providing weather observations collected from both private and public weather stations from all over the world. Being based on a crowdsourced data collection strategy, information is delivered with no quality standard certification. Weather observations are publicly shared through the Weather Underground API, which allows requesting data at no cost for non-commercial purposes and within the limits expressed by the API provider. Because of new company policies, starting from June 2018 WU is no longer providing free API keys. All the data used in this study was acquired before this policy change. WU temperature time series for the stations of interest in Milan are downloaded in comma-separated values (CSV) format using a custom JavaScript collector module developed by the authors. The collected series refer to the period 1 January to 31 December 2016. Temperature measures from both ARPA and WU are available with a sub-hourly frequency. Stations locations are also retrieved and organized in a separate table linked with the time series CSV table for both data sources. The distribution of ARPA and WU stations providing temperature observations in Milan is depicted in Figure 2. The satellite basemap clearly shows that the stations in the South and South-West sides of the study area are mainly located in rural or not heavily urbanized areas. \begin{table}
\begin{tabular}{c c} \hline \hline
**Acquisition Date** & **Synoptic Parameters** \\ \hline \multirow{4}{*}{13-01-2016} & Geopotential height 500 hPa: 5450 m (\(\downarrow\)) \\  & Wind Direction 500 hPa: 315 deg \\  & Advection 850 hPa: Cold \\  & Thermodinamical Profile: Stable \\ \hline \multirow{4}{*}{18-03-2016} & Geopotential height 500 hPa: 5560 m (\(\leftrightarrow\)) \\  & Wind Direction 500 hPa: 105 deg \\  & Advection 850 hPa: No advection \\  & Thermodinamical Profile: Stable \\ \hline \multirow{4}{*}{22-05-2016} & Geopotential height 500 hPa: 5740 m (\(\uparrow\)) \\  & Wind Direction 500 hPa: 200 deg \\  & Advection 850 hPa: Warm \\  & Thermodinamical Profile: Stable \\ \hline \multirow{4}{*}{22-06-2016} & Geopotential height 500 hPa: 5890 m (\(\uparrow\)) \\  & Wind Direction 500 hPa: 20 deg \\ \cline{1-1}  & Advection 850 hPa: Warm \\ \cline{1-1}  & Thermodinamical Profile: Stable \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Synoptic conditions at the acquisition dates of of the satellites [34; 35].