Spatiotemporal patterns in water yield from the humid puna: a case study in the agrarian district of Zurite, Perú

The humid puna is a seasonally dry alpine grass- and shrub-land biome that exists at the altitudinal limits of plant survival, hosts peat-forming wetlands known as bofedales, and yields water to streams used by small and large communities throughout the central and southern Peruvian Andes. Despite the importance of the humid puna in supplying water resources, particularly to perennial streams, few studies have quantified water yield and no studies have explored relationships between the structure of puna landscapes and spatial patterns in water yield. Zurite (population: 3,640, elevation: 3,011 m.a.s.l., annual precipitation: 855 mm) is an agrarian district in the department of Cusco, Perú that derives water resources from the Upper Ramuschaka Watershed (URW, area: 2.12 km2, mean elevation: 4,332 m.a.s.l.), a humid puna headwater catchment with 11.5% coverage of seasonally saturated bofedales. The URW provides an opportunity to explore the hydrology of the Andean puna, and to present baseline water resources data to the community of Zurite to guide sustainable water management and resiliency to a changing climate. Our study sought to: a) Determine the total, wet, and dry season water yield and derive annual water balances from in-situ measurements in the URW; b) Explore the temporal phases of the URW annual water balance; c) Identify relationships between spatiotemporal patterns in water yield and the presence of bofedales; and d) Estimate seasonal dynamic water storage contributions to dry season runoff from bofedales in the URW. We monitored precipitation inputs, seasonal dynamics in subsurface moisture, groundwater, and streamflow for two years, and took distributed discharge measurements at 18 subbasins nested throughout the Central and Eastern tributaries of the URW from June 2019 - January 2021. Over the course of four field campaigns spanning wet and dry seasons, we flew an unmanned aerial vehicle (UAV) to generate a 1-m resolution digital elevation model (DEM) for topographic analyses, and measured material and hydrologic properties in bofedales via direct measurements and downhole nuclear magnetic resonance (NMR). The URW received 749 mm annual precipitation in WY2019 and 825 mm in WY2020. Annual runoff ranged from 62% to 80% of the annual water balance, with dry season runoff accounting for between 11% and 19% of annual runoff. Spatiotemporal analysis of water yield throughout the URW revealed that subbasins with a greater proportion of bofedal land cover yielded greater unit runoff and that this relationship strengthened through the dry season. We estimated seasonal dynamic water storage across all bofedales of the URW to account for 50 - 60 mm of streamflow contributions, or approximately one half of dry season runoff. Collectively, these results suggest: a) water yield from headwater humid puna catchments can represent 60-80% of annual precipitation, and b) bofedales integrate groundwater resources from upslope contributing areas 4 – 12 times their area, store water primarily in high porosity peat, and release water through low conductivity clay rich deposits, sustaining baseflow. Regional research and management efforts should design monitoring programs to improve baseline bofedal hydrology data sets and specifically incorporate bofedales in conservation initiatives due to their role in sustaining dry season streamflow in the puna