Seasonal estimation of groundwater vulnerability

Index-based methods estimate a fixed value of groundwater vulnerability (GWV); however, the effects of time variations on this estimation have not been comprehensively studied. It is imperative to estimate a time-variant vulnerability that accounts for climatic changes. In this study, we used a Pesticide DRASTICL method separating hydrogeological factors into dynamic and static groups followed by correspondence analysis. The dynamic group is composed of depth and recharge, and the static group is composed of aquifer media, soil media, topography slope, impact of vadose zone, aquifer conductivity and land use. The model results were 42.25-179.89, 33.93-159.81, 34.08-168.74, and 45.56-205.20 for spring, summer, autumn, and winter, respectively. The results showed a moderate correlation between the model predictions and observed nitrogen concentrations with R² = 0.568 and a high correlation for phosphorus concentrations with R² = 0.706. Our results suggest that the time-variant GWV model provides a robust yet flexible method for investigating seasonal changes in GWV. This model is an improvement to the standard index-based methods, making them sensitive to climatic changes and portraying a true vulnerability estimation. Finally, the correction of the rating scale value fixes the problem of overestimation in standard models.