Extreme Partitioning of Relic and Contemporary Waters in Arid Environments

Abstract Deciphering the dominant controls on groundwater-surface water-climate connections is critical to understanding water cycles in arid environments, yet persistent uncertainties remain. The growing demand for critical minerals such as lithium and associated water demands has amplified the urgency to address these unknowns. We present an integrated hydrological analysis of the Dry Andes utilizing a uniquely large and comprehensive set of tracer data (3H, 18O/2H) and physical observations. We find two strongly decoupled hydrological systems which interact only under specific hydrogeological conditions where preferential conduits have developed. These conduits which efficiently transport contemporary water (wks to yrs old) in the system control the interplay between modern hydroclimate variations and groundwater aquifers. Contemporary waters account for a small portion of basin budgets but are critical to sustaining surface waters, as a result, these systems are sensitive to short-term climate and anthropogenic perturbations. This framework describes a new understanding of dominant controls on natural water cycles intrinsic to these arid mountain systems.