Mapping and assessing soil sealing in Padua municipality through biotope area factor index

Soil sealing is a worldwide phenomenon of covering of natural or seminatural soil with impervious surfaces, such as built-up or paved surfaces. It is widely recognized as a major environmental issue which drives landscape fragmentation and ecosystem services degradation and loss. Italy is one of European countries with the highest extent of soil sealing. The most affected area is northern Italy, especially the Po Valley with more than 12% of sealed surfaces. According to official data, Veneto Region and the city of Padua are seriously affected by this phenomenon. The Biotope Area Factor is a consolidated ecological urban index for mapping soil sealing, adopted in different European cities to support urban planning; it expresses the ratio of the ecologically effective surface area in relation to the total land area according to land cover classes. The general aim of this study is to map and to assess soil sealing in the whole municipal territory of Padua using the Biotope Area Factor (BAF) index. We tested and adopted a digital land cover map together with aerial images to perform a BAF analysis on the whole municipal territory of Padua. By using sample areas previously analyzed, we validated our source data by a double spatial validation process; therefore, soil sealing analysis was scaled-up to the municipality territory. Results show that in the city of Padua, the average BAF index value is 0.6; totally permeable surfaces (BAF = 1) cover 59.5%, whereas totally "sealed" surfaces (BAF = 0) are 40.3% of the municipal territory (93 km2). Most of the sealed soil is located in the east sector and in the historical core of the city, with BAF values ranging from 0 to 0.2. A particularly critical area is identified within the new industrial area of the city, which is strongly affected by soil sealing. BAF maps are useful tools to identify critical areas by geovisualizing surface permeability at a very detailed scale and by enabling further analyses for hydrogeological risk assessment and urban climate regulation. Moreover, the use of BAF maps at urban scale today represent an important tool for urban management, especially for policy makers who are planning mitigation and compensation measures to control soil sealing.