Modelling for conceptualisation and management of coastal plain aquifers under the risks of global change and deep thermal waters

Climate change and land use transitions intensify groundwater management challenges in coastal aquifers, where natural recharge is declining and irrigation demand is rising. These pressures are further compounded by deep thermal groundwater upflow, which alters aquifer temperature, salinity, and density-driven flow. This study presents a comprehensive approach finalised to the numerical assessment of the Gioia Tauro coastal aquifer system (southern Italy), which is affected by global change and geogenic thermal water contributions. A variable-density groundwater flow model was developed using SEAWAT, informed by hydrogeological data, land use mapping, and future climate projections. The conceptual model of the aquifer was validated and used to quantify the effects of thermal water upflow and projected climate impacts on groundwater dynamics. The model included steady-state simulations (1950–2000) to represent past conditions and calibrate the system, followed by transient simulations for predictive scenarios through 2100. Results quantify the deep thermal inflow, contributing ∼4.35 % of total groundwater inflow, raising salinity and temperature in fault-controlled zones. By 2100, effective rainfall is expected to decline by 21 %, resulting in a 0.3 m average decline in hydraulic heads and a 76.5 % increase in salinity within the shallow aquifer. These findings highlight the compounded effects of climate variability, land use intensification, and thermal water intrusion on coastal groundwater systems and the proposed approach’s effectiveness in assessing deep thermal flow yield and its salinity and thermal effects. This study underscores the need for integrated, adaptive management strategies to mitigate aquifer depletion and salinisation in similar coastal settings worldwide.