Importance of temporal dimension and rural land cover when computing surface urban Heat Island intensity

Surface urban heat islands (SUHI) translate the difference in surface temperature between urban and surrounding rural regions. This study makes use of geostationary remote sensing data (Meteosat Second Generation) rather than polar orbiting satellites, taking advantage of its higher temporal resolution. Three cities were selected: Paris, Madrid and Milan. This allowed studying both the seasonal and diurnal cycles of SUHI. The SUHI is here computed with reference to the agricultural and forest rural land covers, and the two combined. We found that for a generic rural background, the SUHI maximum occurs at 12/20/12 UTC in spring/spring/summer with values of 3.1/1.6/4.0 degrees C for Paris/Madrid/Milan. Secondary peaks of SUHI are also sometimes found during the nighttime in the cities of Paris and Milan. Our results highlight the need for understanding the diurnal variability of SUHI throughout the year, considering the different city surroundings. It is found that for the same urban temperature, different SUHI intensities can occur when varying the rural cover reference. Also, for the same urban temperatures, neither SUHI intensity, nor its diurnal cycle is constant throughout the year, emphasizing the need for high temporal resolution datasets in SUHI studies.