A modelling approach combining swat with Gis-based DRASTIC techniques to assess aquifer vulnerability evolution in highly anthropised aquifers

Groundwater resources are vital for human development, particularly in arid and semi-arid regions with limited water availability. This study examines the evolution of aquifer vulnerability in the Miranda basin by addressing the critical interaction between land use and water quality amidst increasing pressures on water resources, with a focus on the impact of historical land use changes and agricultural practices on groundwater quality in the Campo de Cartagena aquifer, which drains into the degraded Mar Menor coastal lagoon in southern Spain. To evaluate aquifer vulnerability, this research employs the DRASTIC vulnerability assessment method, which is based on seven hydrogeological parameters. This theoretical framework allows for a comprehensive analysis of the interactions between land use changes, water management, and aquifer health, which deepens the understanding of the factors driving vulnerability over time. A key component of the methodology is the use of the Soil and Water Assessment Tool (SWAT) to estimate aquifer recharge and generate reliable maps that depict this essential parameter. The study reveals significant results through an extensive analysis of vulnerability changes over the past 70 years, which shows that high vulnerability areas have increased from 11%, prior to the Tagus-Segura water transfer in 1979, to 53% today. In contrast, low and moderate vulnerability areas have decreased by 15% and 28%, respectively. This shift is primarily attributed to intensified agricultural practices, which lead to enhanced aquifer recharge and elevated piezometric levels, which increase contamination risks, as demonstrated by the severe eutrophication observed in the Mar Menor. Moreover, the accuracy of the vulnerability maps is validated by comparing them with observed nitrate concentrations in groundwater, which reveals a strong correlation (R² = 0.86). The methodology provides essential insights for policymakers and supports the implementation of land use restrictions to mitigate groundwater contamination risks. The findings ultimately underscore the necessity for integrated water management strategies that balance agricultural productivity with ecological sustainability in water-scarce environments.