Mountain catchments are key freshwater suppliers to lowland urban populations, sustaining key ecosystem services, particularly in seasonally semiarid environments where potential evapotranspiration (PET) exceeds precipitation (P) for most of the year. However, the biophysical controls that enable snow-free mountains to maintain year-round positive water yields remain poorly understood. In this study, we analyse the water yield of 25 mountain catchments along a climatic gradient of central Argentina, precipitation ranges from 350 to 850 mm/year. We combine long-term hydrometric records with catchment biophysical descriptors of climate, topography, land cover, morphometry and lithology to identify the main drivers of water yield and related hydrologic signatures. Observed water yields varied widely across catchments (7 to 674 mm/year) and often surpassed estimates from extensively used theoretical and empirical hydrological models (i.e., Budyko's envelope, Fu's curve and Zhang's watershed synthesis), highlighting the key role of local biophysical mountain features, generating flow. Generalised linear models identified mean annual precipitation and the fraction of exposed rock as the strongest positive predictors of water yield, while the aridity index (PET/P), woody vegetation cover and drainage density were negatively associated with water yield. Hydrologic signatures further revealed that baseflow increases with elevation range, driving groundwater transport through enhanced hydraulic gradients, while herbaceous vegetation promotes infiltration and sustains higher baseflows. Catchments with higher aridity and woody vegetation cover showed greater dry-season water yield fractions, highlighting the importance of low flows in these systems. By contrast, in more subhumid catchments, topographic attributes such as steep slopes and valley extent emerged as dominant drivers of runoff generation, in clear contrast to the fraction of flatlands. Comparisons with adjacent lowland systems evidenced that the topography, rocky outcrops and vegetation of the studied mountain landscapes substantially increase water yields, underscoring their critical hydrological and ecological role in the region.