Automated ice ablation readings reveal the significance of summer heat waves for glacier melt

Summer heat waves have a substantial impact on glacier melt as emphasized by the extreme summer of 2022 that caused unprecedented mass losses to the Swiss glaciers. Despite the dramatic impact on glaciers, the summer of 2022 offered a unique opportunity to analyze the implications that such extraordinary events have on glacier melt and related runoff release.

This study presents a novel approach based on computer-vision techniques for automatically determining daily mass balance variations at the local scale. The approach is based on the automated recognition of color-taped ablation stakes from camera images acquired at six sites on three Alpine glaciers in the period 2019-2022. The validation of the method revealed an uncertainty of the automated readings of ±0.81 cm d^-1. By comparing the automatically retrieved mass balances at the six sites with the average mass balance of the last decade derived from seasonal in situ observations, we detect extreme melt events in the summer seasons of 2019-2022.

The in-depth analysis of summer 2022 allows us to assess the impact that the summer heat waves have on glacier melt. With our approach we detect 23 days with extreme melt over the summer, emphasizing the strong correspondence between heat waves and extreme melt events. The Swiss-wide glacier mass loss during the 25 days of heat waves in 2022 is estimated as 1.27 ± 0.10 Gt, corresponding to 35% of the overall glacier mass loss in the summer of 2022. As compared to the 2010-2020 average glacier mass change, days with extreme melt in 2022 correspond to 56% of the mass change during the summer period, thus demonstrating the significance of heat waves for seasonal melt.