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, geological, and glaciological drivers with streamflow generation. 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 streamflow data 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 calibrated temperature-index melt model parameters within a semi-lumped modeling framework. We focus on evaluating the melt 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, implementing three variants of a temperature-index snow and ice melt model (the classical degree-day model, the aspect-related model, and the Hock temperature-index model). Through an analysis of streamflow simulations, benchmark metrics consisting of resampled and bootstrapped discharge time series, and model performance metrics, we demonstrate that robust parameter transferability and accurate streamflow simulation are possible across diverse spatial scales. This finding is conditional upon the melt model applied, with melt models using more spatial information leading to convergence of the model parameters until we observe overparameterization. We conclude that simple semi-lumped models can be used to extend hydrological simulations to ungauged catchments in alpine regions and improve high-elevation water resource management and planning efforts, especially in the context of climate change.