GROUNDWATER VULNERABILITY ASSESSMENT USING STATISTICAL METHODS

Groundwater vulnerability maps are considered as an essential component for sustainable environmental planning and management. Statistical methods are increasingly being used to produce scientifically defensible groundwater vulnerability maps which meaningfulness and reliability however must be carefully evaluated before being distributed. The Weigth of Evidence method (WofE) was used for assessing groundwater vulnerability to nitrate contamination of two different aquifers with the aim of testing its robustness as exploratory and predictive tool and addressing more general issues related to the use of statistical methods to produce groundwater vulnerability maps. The spatial variability of different maps showing similar performances in term of predictive power, the influence of using different thresholds in the analysis, and the limits of using statistical methods to assess groundwater vulnerability were the main aspects evaluated in this study. Results showed that: a) the WofE represents a powerful tool for selecting the appropriate explanatory variables and producing reliable maps; b) different maps, generated using different combinations of explanatory variables, always present some degree of spatial variability that can be analyzed through multiple validation techniques; c) the use of different thresholds produce similar or different results depending on if the spatial distribution of the vulnerability is observed at broad and small scale, respectively. Furthermore, a new research challenge was identified in trying to integrate the temporal component in the vulnerability analysis.