Hydrological Partitioning and Subsurface Water Storage in Puna Andean Grasslands Revealed by a Paired Catchment Approach

Mountain headwaters in the tropical Andes are vital for regional water security, yet the extensive Puna grassland biome remains largely understudied. To help address this gap, we employed a paired-catchment design in two Peruvian Puna catchments and used high-resolution hydrometric data, over the period [2012–2014] at hourly time-step, to investigate controls on hydrological partitioning and subsurface storage. Our findings provide a field-based perspective on the classic ‘sponge versus pipe’ paradox by showing that peat-forming wetlands (bofedales) perform a dual hydrological role. Their saturated surfaces act as efficient ‘pipes’ that enhance event runoff, while their porous subsurface provides event-scale buffering that dampens hydrograph recessions, defining them as seasonal buffers rather than long-term dry-season stores. Streamflow recession analysis further supports a dual-reservoir conceptualization, in which infiltrated water is partitioned between a shallow system connected to local streamflow and a deeper system linked to regional groundwater recharge. The catchment with greater apparent percolation capacity produced lower annual water yield, consistent with a ‘leaky’ catchment interpretation involving inter-catchment groundwater flow that bypasses the topographic outlet. Our comparison also suggests that the naturally flashier response of this catchment may be further accentuated by more intensive grazing, although this land-use signal should be interpreted as secondary to hydrogeomorphic controls. Overall, the results indicate that hydrological functioning is organized hierarchically: subsurface and surficial hydrogeomorphic setting controls the distribution of bofedales and flow paths, while land use modulates the resulting response. This perspective reframes Puna headwater catchments as three-dimensional systems characterized by a trade-off between local streamflow resilience and regional aquifer recharge, underscoring the need to preserve bofedal connectivity and mitigate soil-degrading land uses.