Characterizing Hydrological Drivers of the Andean Precipitationshed: Integrating Moisture Tracking and Stable Isotopes to Disentangle Precipitation Amount, Altitude, and Temperature Effects.

High-altitude tropical ecosystems, such as the Andean Páramo, play a fundamental role in regional hydrological regulation and the provision of essential ecosystem services.Traditionally, the characterization of these rainfall-runoff systems has focused on terrestrial catchment controls—including vegetation-soil complexes, topographic gradients, and hydrogeological baseflow—to understand water movement within the Area of Interest (AOI). However, the corresponding 'precipitation watershed' (the atmospheric moisture source) remains largely uncharacterized in terms of its own hydrological drivers. While terrestrial basins characterize their hydrological response through discharge dynamics and evapotranspiration fluxes, the precipitation watershed is effectively probed through a stable isotope approach to decouple its governing controls—such as precipitation amount, temperature, and altitude—encoded within the meteoric isotopic signature.

Addressing this gap, this investigation utilizes the WAM-2Layers Eulerian moisture tracking model to characterize the hydrological drivers and transport pathways for the Chingaza Páramo 'precipitationshed'. This integrated tracking approach provides the essential provenance context required to interpret isotopic data from both geographic and hydrological perspectives, allowing for a comprehensive evaluation of how moisture origin and transport history are manifested within the environmental signature of meteoric waters. To ensure model consistency, isotopic data were collected at dual daily and monthly frequencies, purposefully aligned with the temporal timestamps and 'sink' settings of the WAM-2Layers model.

By leveraging this spatio-temporal alignment, the study analyzed isotopic compositions concurrently with the precipitation, elevation, and temperature history along the moisture trajectories en route to the Chingaza Páramo. The integration of these variables into novel hydrological driver archetypes enabled a detailed characterization of the atmospheric environmental signature. Preliminary results demonstrate the robustness of this classification framework when mapped against the Global Meteoric Water Line (GMWL). For the monitored period, the daily sampling characterization identified a dominance of warm-source trajectories (63%), followed by mixed (19%) and cold-source (16%) archetypes, with moisture provenance primarily originating from the Atlantic Ocean. The distribution of these samples within the stable isotope biplot (d18O vs. d2H) effectively illustrates the transition between enrichment and depletion phenomena, underscoring the potential of this approach to quantify the influence of atmospheric drivers on Andean meteoric water behavior.