Impact of changing rainfall patterns on groundwater recharge in semi-arid dune landscapes

Abstract Climate-induced changes in rainfall patterns, particularly increases in event intensity and altered seasonal distribution, pose significant challenges for groundwater recharge and water resource management, especially in semi-arid Mediterranean environments. This study was motivated by the pronounced scarcity of long-term field data quantifying how rainfall intensity and vegetation cover interact to shape the soil water budget and diffuse recharge under natural conditions. To address this gap, a 3-year lysimeter experiment was conducted in the aeolian dune system of Doñana National Park (SW Spain), utilizing four precision weighable lysimeters of different sizes and vegetation covers (bare soil, pine canopy, and shrubland). Meteorological and hydrological variables were continuously monitored, allowing detailed partitioning of precipitation, evaporation, and drainage at high temporal resolution. The results show that a small number of high-intensity storms (> 20 mm/day) dominated annual rainfall input and were responsible for most groundwater recharge, whereas low-intensity rainfall contributed negligibly to recharge. Bare-soil lysimeters exhibited consistently high and stable recharge rates (50–55% of rainfall), while vegetated lysimeters showed much lower and more variable recharge (11–60%), with intense storms effectively bypassing interception and transpiration limits. These findings illustrate that vegetation cover critically modulates the effect of rainfall intensity on recharge, with groundwater input under vegetation potentially matching bare soil recharge when intense events are frequent. This insight has important implications for understanding and managing groundwater resources in sandy, semi-arid regions undergoing climate-driven changes in rainfall regime.