Spatial and temporal trends of the surface and air heat island over Milan using MODIS data

Abstract

In this work the analysis of the surface and air heat island in Milan, Italy, by means of satellite maps is proposed. The urban heat island (UHI) maps were produced using data provided by the Moderate-resolution Imaging Spectroradiometer (MODIS) on board of both Terra and Aqua satellites. Two types of UHI were analyzed simultaneously: the canopy layer heat island (CLHI) and the surface urban heat island (SUHI). The aim of this work is the realization of the SUHI and CLHI maps to monitor the spatial and temporal evolution of surface and air heating; also, to highlight and quantify the different features (e.g. magnitude, spatial extent, orientation and UHI center location) a Gaussian surface was used to fit the spatially distributed heat island patterns.The analysis during summer months points out that the SUHI effect is a noticeable phenomenon throughout the whole diurnal cycle: it has a stronger intensity in the daytime with peaks around 9–10K while in the nighttime, in the absence of solar forcing, it decreases by a factor of 2. In contrast, the canopy layer heat island during the daytime is absent: the CLHI emerges after sunset with an average intensity around 3–4K, showing features similar to the nighttime SUHI.In addition, comparisons between UHI intensity and normalized difference vegetation index (NDVI) were performed, confirming that green areas can contribute to the mitigation of this phenomenon.