Use of data from the advanced spaceborne thermal emission and reflection radiometer (ASTER) for the study of the urban heat island (UHI) in Bragança (Portugal) (2000-2023)

The Urban Heat Island (UHI) effect refers to the temperature difference between urban and surrounding rural areas, with higher temperatures in urban areas, especially after sunset. The Surface Urban Heat Island (SUHI), a proxy for UHI, can be evaluated using Remote Sensing (RS) data by calculating the Land Surface Temperature (LST). Bragança (Portugal) has an in situ network, with 23 sensors installed in 2011, classified into seven different Local Climate Zones (LCZs), to measure Air Temperature (T_air). The primary objectives of this study were to: i) calculate the LST using Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data available on Google Earth Engine (GEE) from 2000-2023 at these 23 points, divided into spring/summer (a); and autumn/winter (b); ii) calculate and analyze the Intensity of SUHI (SUHI_int) (2000-2023), using LST, based on the temperature difference recorded at each sensor compared to the average temperature at the Rural Areas (RCD) sensors, and evaluate the thermal behavior in the LCZs; iii) calculate the UHI (UHI_int), using T_air data; and iv) correlate SUHI_int and UHI_int (2011-2023). As a result, 17 images from (a) and four from (b) were processed, and the highest LST medians were associated with classes featuring anthropogenic elements in both, with (a) being more heterogeneous. Comparisons between SUHI_int and UHI_int, were obtained in 13 days, only from (a). The highest median temperature values were in anthropogenic classes. The correlation between SUHI_int and UHI_int was "strong" (74%) and "very strong" (26%), confirming their similarity in thermal behaviour.