On thin glacial ice: New Austrian Glacier Inventory shows accelerating glacier shrinkage and 31% area loss within two decades

Abstract. We present the new Austrian glacier inventory, AGI 5. Glacier outlines were manually digitized from high-resolution orthoimagery and digital elevation models (DEM), using older inventory data as a baseline. The delineation of debris-covered ice was supported by visual analysis of multi-temporal imagery and DEM differencing, depending on data availability. We assessed discrepancies with older inventories and differences in interpretation between analysts using a round robin experiment (mapping of selected glaciers by several analysts). The updated inventory reflects glacier extent in 2023 (55 % of total glacier area in the study region), 2022 (43 %), and 2021 (2 %). The total glacier area in AGI5 is 285±12 km². Most glaciers in Austria (87 %) are smaller than 0.5 km². These "very small" glaciers comprise 22 % of the total glacier area. Nine glaciers remained larger than 5 km² and account for more than a quarter of Austria's glacierized area. Area losses since the previous inventory (2004–2012) amount to 129±23 km², corresponding to 31 % of the total glacier area. Median area loss rates differ between regions, ranging from 2–3 % per year in more heavily glacierized regions to almost 7 % per year in regions with smaller glaciers. Of 894 glaciers listed in the previous inventory, 95 have disappeared completely or were no longer mappable. Compared to other glacierized regions, Austria's glacier recession since the Little Ice Age (LIA) maximum is well constrained with a LIA inventory, four high-resolution, consistent AGIs from 1969 to 2022/23, and additional coverage in complementary inventories using different data sources. As glacier loss accelerates, more frequent updates to the AGIs are needed to keep pace with rapid changes.