Preliminary analysis of urban surfaces for the characterizaͳ tion and the mitigation of the heat island effect

The urban heat island (UHI) phenomenon is an issue of growing interest and the subject of numerous studies. UHI is defined as the metropolitan area that is significantly warmer than its surrounding rural areas. UHI has significant impacts on the buildings energy consumption and outdoor air quality, therefore it is considered an important environmental topic. The most effective approaches to mitigate UHI include, among others, the albedo increase of materials used for manmade surfaces (e.g. pavements, roofs), the increment of vegetated areas (e.g. parks, flowerbed, gardens), the increment of water surfaces (e.g. ponds). The UHI mitigation results in a reduction of the energy consumption and in an improvement of outdoor air quality. A recent model study carried by Rossi et al. (CIRIAF, University of Perugia) correlated the increase of materials albedo with energy saving in terms of reduction of carbon dioxide emissions. Therefore surfaces characterization is an useful information for planning UHI mitigation actions. Albedo of different types of urban surfaces can be obtained from bibliographic data, from laboratory measurements or retrieved from spaceborne or airborne remote sensing data. This data reported surface reflectance for each band, from which albedo can be directly obtained. In this work, airborne remote sensing data have been used for UHI characterization and for the study of UHI mitigation. The area of interest is the city of Modena in the Emilia Romagna region (Italy). On this area four orthorectified images acquired in the electromagnetic regions of the visible and near-infrared by an airborne sensor with a spatial resolution of 2 meters are used. Using an object-oriented technique, the four images have been segmented and classified into categories representing different types of land cover significant for UHI: Cultivated Soils, Green Areas, Roads, Parking, Railways and Buildings. The "Buildings" class is further divided in pitched roofs made of tiles (typical buildings of the historical center of the city) and in flat roofs of industrial buildings with both bright and dark coverings. This information will be used in the model described above in order to study UHI mitigation. This study presents some preliminary results of the application of this methodology that will be developed in the upcoming years for the application to various sites of interest.