Understanding groundwater-surface water interactions is essential for sustainable water management in semiarid regions, particularly in southern Europe, where water scarcity is increasing. Accurate knowledge of groundwater-river interactions is necessary to developing realistic conceptual models. The study focuses on the Mundo River in southeast Spain and its relationship with the scarcely gauged Alcadozo aquifer, characterized by fractured carbonated formations. To assess flow paths, recharge sources, residence times and groundwater-river interactions, major ions, stable isotopes (delta 18O, delta 2H), tritium (3H), strontium isotopes (87Sr/86Sr), and radon (222Rn) was measured in 143 groundwater and 24 surface water samples in period 2008-2014. Principal Component Analysis (PCA) was a paramount tool identifying zones of diffuse and concentrated groundwater discharge to the Mundo River. Findings reveal that groundwater discharge occurs primarily concentrated in the central zone while being more diffuse in the eastern and western parts. Hydrochemical facies and 87Sr/86Sr indicate that discharging groundwater in the western part results from water-rock interactions, whereas the central and eastern segments are affected by agricultural influences. Tritium indicates that the discharging groundwater is relatively young and distinguishes between two groups with varying residence times: one representing currently recharged groundwater and the other linked to older groundwater with 1-3 half-life periods. The conceptual model supported by PCA illustrates that the Mundo River is sustained by groundwater contributions from varied flow paths, influenced by precipitation, topography, and rock fractures. The study provides essential insights for future management of water resources in regions with limited groundwater monitoring, especially under climate and land-use pressures.