Effects of urban changes on groundwater vulnerability, a case study in Lombardy (Italy)

Urban sprawl is one of the most important types of land-use changes currently affecting Europe with important impacts on groundwater quality. The area of the Po Plain in northern Italy is one of the most populated areas in Europe and can be considered as a representative area to study urban sprawl impacts on groundwater quality. The identification of areas where groundwater is characterized by a degradation of the water quality is required by two European Union Directives (2000/60/EC and 2006/118/EC). Here, we present a time-dependent groundwater vulnerability assessment of the Po Plain area of Lombardy region, concerning the period 2001–2011. Three different variables have been selected, and compared to each other, in order to investigate the evolution of urban nitrate non-point sources: urbanization derived from satellite scatterometer data (QuikSCAT-DSM data), population density changes calculated using two successive national censuses (database ISTAT) and land-use changes derived from photo-interpretation of aerial imageries (database DUSAF). Four other variables, considered not being time-dependent for the purpose of this study, have been identified to represent the geological and hydrogeological conditions of the study area: soil protective capacity, groundwater depth, groundwater velocity and hydraulic conductivity of the vadose zone. Groundwater vulnerability is assessed through the spatial statistical method Weights of Evidence (WofE). WofE enables observations of the individual role and the combined effect of both urban change and geological factors considered in the analysis in relation to the change of nitrate concentration in the decade 2001–2011. Time-dependent groundwater vulnerability maps for the study area have been produced and compared.