Water balance dynamics in adjacent glaciated and unglaciated high arctic catchments (SW Spitsbergen, Svalbard)

Study region Hornsund, SW Spitsbergen, Svalbard – area representing the Atlantic sector of High Arctic Study focus Rapid climate warming across Svalbard is fundamentally altering high-latitude terrestrial cryospheric systems and hydrological processes. To investigate these transitions, a seasonal moving-parameter HBV modeling framework was implemented to evaluate and compare the long-term water balance dynamics of two adjacent catchments underlain by continuous permafrost: the unglaciated Fuglebekken catchment (monitored 2014–2024) and the glaciated Ariebekken catchment (monitored 2007–2024). New hydrological insights The findings suggest a structural divergence in the runoff regimes of these neighboring watersheds. While the unglaciated Fuglebekken regime is driven by seasonal snowmelt and rainfall events, the glaciated Ariebekken system benefits from a substantial glacial meltwater buffer that sustains high, steady baseflow late into the summer. Crucially, Fuglebekken shows a significant positive multi-annual storage gain over the study period (+325 mm), challenging the traditional baseline assumption of negligible annual storage changes (ΔS = 0) in continuous permafrost catchments. This net water accumulation could be consistent with localized active layer thickening and talik development. Methodologically, the integration of intra-annually shifting parameter sets allows the model to represent the non-stationary hydrogeological features of permafrost soils. Additionally, updating the model via an area-scaling glacier module accurately represents the retreat of the Ariebreen glacier, providing a physically plausible meltwater input and highlighting the transient nature of current high-discharge volumes in the deglaciating catchment.