Comparison between surface and canopy layer urban heat island using MODIS data

Urban heat island (UHI) maps were produced over the city of Milan, Italy, using data provided by the Moderate-resolution Imaging Spectroradiometer (MODIS). Two types of UHI were analyzed simultaneously: the canopy layer heat island (CLHI) and the surface urban heat island (SUHI). The SUHI and CLHI maps allow to monitor the spatial and temporal evolution of surface and air heating and also to highlight the different features (e.g. magnitude, spatial extent, orientation and UHI centre location) using a Gaussian surface fitting. This results indicate that the SUHI effect is a noticeable phenomenon throughout the whole diurnal cycle: it has a stronger intensity in the daytime with peaks around 9-10 K while in the nighttime it decreases by a factor of 2. In contrast, the CLHI during the daytime is absent and after sunset shows features similar to the nighttime SUHI. Although the 1-km spatial resolution of MODIS may represent a limitation for a finer scale analysis, the four daily passes are essential to monitor the urban heat island at different times during the day.