An increasing role of subsurface processes in the water circulation in the High Arctic catchment – the results from Fuglebekken, SW Spitsbergen

Abstract

Changes in the depth of the active layer thickness (ALT) in Arctic and permafrost regions significantly impact the transformation of rainfall into runoff. Due to climate change, permafrost thawing and ALT alterations modify how water is transported and stored within catchments, affecting surface and subsurface hydrological processes. This study investigates the associations between temporal changes in active layer thickness, hydrological model parameters, and variations in catchment responses. The study area covers the unglaciated catchment Fuglebekken, located near the Polish Polar Station Hornsund on Spitsbergen. For hydrological modelling, the conceptual rainfall-runoff HBV model was used. Model calibration and validation were carried out on runoff data within subperiods. A moving window approach (3-week duration) using data from the summer seasons 2014-2023 was applied to derive temporal variations of parameters. Model calibration, along with an evaluation of parametric uncertainty, was performed using the Shuffled Complex Evolution Metropolis algorithm. A comprehensive investigation of the temporal variability of HBV model parameters demonstrated consistency in the results. The smallest parametric uncertainty and the largest temporal changes were estimated for the parameter KS representing a slow runoff reservoir. Temporal variability of the KS parameter is characterized by the presence of two maxima, the first maximum at the beginning of the ablation season (due to snowmelt and ice-rich permafrost thawing) and the second maximum in September (a result of high precipitation). The temporal variability of other parameters was smaller and usually within their parametric uncertainty. In addition, the use of the HBV model allowed for the assessment of water storage in five conceptual reservoirs characterizing catchment processes. The outcomes highlighted large changes in slow runoff reservoir, demonstrating an increasing significance of subsurface processes in the water circulation in the High Arctic catchment.  The study was supported by the Polish National Science Centre (grant no. 2020/38/E/ST10/00139).