Heat wave contribution to 2022’s extreme glacier melt from automated real-time ice ablation readings

Abstract. Accelerating glacier melt rates were observed during the last decades. Substantial ice loss occurs particularly during heat waves that are expected to intensify in the future. Because measuring and modelling glacier mass balance at the daily scale remains challenging, short-term mass balance variations, including extreme melt events, are poorly captured. Here, we present 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, and is tested and validated at six stations installed on three Alpine glaciers during the summers of 2019–2022. Our approach produces daily mass balance with an uncertainty of ±0.81 cm w.e d⁻¹, which is about half of the accuracy obtained from manual read outs. The automatically retrieved daily mass balances at the six sites were compared to average daily mass balances over the last decade derived from seasonal in situ observations to detect and assess extreme melt events. This allows analyzing the impact that the summer heat waves which occurred in 2022 had on glacier melt. Our results indicate 23 days with extreme melt, showing a strong correspondence between the heat wave periods and extreme melt events. The combination of below-average winter snow fall and a suite of summer heat waves led to unprecedented glacier mass loss. The Swiss-wide glacier storage change during the 25 days of heat waves in 2022 is estimated as 1.27±0.10 km³ of water, corresponding to 35 % of the overall glacier mass loss during that summer. Compared to the average course of the past decade, the 25 days of heat waves in 2022 caused a glacier mass loss that corresponds to 56 % of the overall mass loss experienced on average during summers 2010–2020, demonstrating the relevance of heat waves for seasonal melt.