Simulating glacier mass balance and its contribution to runoff in Northern Sweden

Glaciers are one of the main sources of freshwater in cold regions. The glacier melting process can significantly impact the glacier mass balance (GMB) and contribute a large amount of runoff in cold regions. This study applied the recently developed semi-distributed glacio-hydrological conceptual model (FLEX^G) to understand the glacier melting process and the effect of topography on GMB in the Torne River basin, northern Sweden. The study simulated glacier and snow accumulation and ablation, as well as runoff from the glacier and non-glacier areas of the basin using the FLEX^G model for the time period 1989–2018. The FLEX^G model considers the influence of topography on runoff generation, and in this study the basin was classified into 143 zones depending on elevation and aspect. In order to gain a comprehensive view of the performance of the FLEX^G model, the classical lumped hydrological model HBV was used and compared with the FLEX^G model in simulating total streamflow and peak runoff at the outlet of the basin. Our results revealed that the FLEX^G model performed well in reproducing the streamflow (also better than the HBV model) with metric Kling-Gupta Efficiency (KGE) of 0.80 and 0.71 for the calibration and validation periods, respectively. We also found that the FLEX^G model performs better in peak runoff simulation than the HBV model. The FLEX^G simulated snow cover area proportion agreed well with the MODIS satellite snow cover product (R² = 0.60 and RMSE = 28%). The GMB in different elevation zones was simulated, and a downward trend was found for GMB changes during the study period because of climate change.