Groundwater/Surface Water Temperature Variations and Hydrogeological Implications in Doñana National Park

This study analyzes the evolution of surface water and groundwater temperatures at various depths in the sand-dune ponds of Doñana National Park (southern Spain) over eight hydrometeorological years (2016–2024). This research aims to characterize the water temperature regime, identify water temperature trends, and analyze patterns in groundwater flow dynamics. The results indicate that, in a recent dry–warm period (2020–2023), coinciding with a notable decrease in precipitation and an increase in the average air temperature in the area, there was an increase in the annual mean temperature of pond water and in shallow piezometers (~15 m depth). However, in deep piezometers, a decrease in water temperature was recorded during the dry–warm period, along with a reduction in temperature variability. A phase shift has also been observed between groundwater temperature extremes and air temperature variations, with the magnitude of this shift depending on sensor depth. These findings enable the analysis of the sensitivity of these wetlands to global environmental change and contribute to the characterization of recharge and discharge flows in the aquifer, both at local and regional scales, allowing for the evaluation of flow variability in hydrological years with below-average precipitation and above-average air temperature and shallow groundwater temperature.