*2.3. Acquisition and Pre-Processing of Satellite Data*

We acquired the Landsat 8 OLI (Operational Land Imager) and TIRS (Thermal Infrared Sensor) images for the same day (4 June 2017; scene ID: LC08\_L1TP\_127045\_20170604\_20170615\_01\_T1), when Hanoi experienced the greatest heat wave in recent 40 years. On that day, the air temperature in Hanoi reached up to 42 ◦C. Since Landsat 8 images were not available for 2 June 2016, the hottest day of 2016, we acquired the Landsat 8 OLI and TIRS images for the second hottest day of 1 June 2016

(scene ID: LC08\_L1TP\_127045\_20160601\_20170324\_01\_T1). For simplicity, 1 June is still named as the hottest day in 2016 hereafter, in the paper. On that day, the air temperature in Hanoi reached up to 39 ◦C. The Landsat 8 image of 2016 are later used to validate the models that are developed from the Landsat 8 images of 2017. The OLI data were converted into Top-Of-Atmosphere (TOA) spectral reflectance, applying the rescaling coefficients that are available in the metadata file. The Landsat 8 images utilized for the study area are cloud-free.
