Characterization of recharge components for delineation of a high-alpine rock glacier spring catchment, Ötztal Alps (northern Italy)

Abstract Rock glaciers provide shallow groundwater reservoirs that affect the hydrology of alpine headwater catchments. However, quantifying and identifying their temporally dominating recharge components, as well as delineating their hydrological catchment, can be challenging. The present study makes use of a lumped-parameter rainfall-runoff model (GR4J-CemaNeige) to tackle these issues, applied at a test site in the Ötztal Alps (northern Italy). The model relies on gridded precipitation and air-temperature data and is calibrated using discharge data. Three different catchment scenarios varying in size and glacier coverage extent were modeled to determine the most likely catchment. The model's outcome was validated using oxygen and hydrogen stable isotopes and electrical conductivity analyses. Three dominant recharge components were quantified by the rainfall-runoff model for the 2012–2021 period: snowmelt (607 mm/year, 56%), rainfall (443 mm/year, 42%), and glacial ice melt (25 mm/year, 2%). The rock glacier permafrost ice melt contributes less than 1% of the total annual discharge, falling within the model uncertainty range. The study demonstrates that a simple rainfall-runoff model helps to identify individual recharge components. It gives a crucial indication for the most likely delineation of a rock glacier spring catchment in a complex periglacial and glacial environment. This provides the basis for quantitatively predicting climate change impact on such highly sensitive environments.