Scale-dependency in modeling nivo-glacial hydrological systems: the case of the Arolla basin, Switzerland

Abstract. Hydrological modeling in alpine catchments poses unique challenges due to the complex interplay of meteorological, topographical, glaciological and streamflow generation factors. A significant issue arises from the limited availability of streamflow data due to the scarcity of high-elevation gauging stations. Consequently, there is a pressing need to assess whether streamflow models that are calibrated with moderate-elevation datasets can be effectively transferred to higher-elevation catchments, notwithstanding differences in the relative importance of different streamflow-generation processes. Here, we investigate the spatial transferability of hydrological model parameters within a semi-lumped modeling framework. We focus on evaluating the model transferability from the main catchment to nested and neighboring subcatchments in the Arolla valley, southwestern Swiss Alps. We use the Hydrobricks modeling framework to simulate streamflow patterns, implementing three variants of a temperature-index snow- and ice melt model (the classical degree-day, aspect-related, and Hock's temperature index). Through a comprehensive analysis of streamflow simulations, benchmark metrics consisting of bootstrapped discharge series, and model performance, we demonstrate that robust parameter transferability and accurate streamflow simulation are possible across diverse spatial scales. This finding is conditional upon the used melt model, with melt models using more spatial information leading to convergence of the model parameters until there is an onset of overparameterization.