Abstract ID: 28.7453 | Accepted as Poster | Poster | 2025-02-28 12:45 - 14:15 | Ágnes‐Heller‐Haus/Small Lecture Room

Glaciers in the European Alps are reflecting the effects of shorter winter periods with reduced precipitation and prolonged summer seasons and rising temperatures. These changes appear to be occurring with greater frequency and intensity in recent years. High-resolution optical satellite data from the Sentinel-2 mission, available since 2015, provide surface observations not only of individual glaciers but also of entire mountain ranges at the same time. The improved temporal resolution of these observations—10-day intervals since 2015, and 5-day intervals since 2017—has significantly increased the availability of cloud-free observations compared to earlier periods, when high-resolution optical satellite data were available only every 16 days. Based on optical satellite imagery, glacier surfaces can be classified into snow, clean ice, and snow-free debris cover. Firn areas, however, can have similar spectral reflectance characteristics as old, dirty snow from the previous winter or bright ice, making it difficult to distinguish between these surface types. To address this, a classification of firn areas using Sentinel-2 data was tested for manually selected dates. In optical satellite data, clouds obscure the Earth’s surface and are thus masked over glaciated regions.
The Sentinel-2 dataset enables the study of changes in glacier surface conditions on multiple dates during the melting season across consecutive years. An analysis of Sentinel-2 time series for glaciers in the Alps from 2015 to 2023 reveals a change in the snow areas on glaciers during the ablation season in recent years. The main ablation period, marked by a significant decrease in snow-covered areas, starts in late May/early June, and ends with a maximum ablation extent in late August/early September across all observed years. However, following the first snow fall event after this main ablation period, occurring typically in early September, a second significant ablation phase has been observed in recent years, which can extend into late October. Although the maximum extent of the ablation area is reached at the end of the main ablation period in all analysed years, significant reduction in snow cover also occurs during the second melt period, exposing large areas of glacier ice. This prolonged melting of snow and ice areas contributes to the reduction of glacier mass.
In this presentation, examples of the glacier surface classifications will be shown, and the temporal and spatial variabilities of the glacier surface classes observed from Sentinel-2 data during the melting periods 2015 to 2023 on selected individual glaciers and for glaciers in selected mountain ranges will be discussed.