The new Swiss Glacier Inventory SGI2020: From a topographic to a glaciological dataset

A glacier inventory describes the extent of all glaciers at a given point in time and in periods of rapid glacier change a frequent update is needed. The Swiss Glacier Inventory 2010 (SGI2010) is the last official inventory for Switzerland and was derived by manual digitization from high-resolution (25 cm) aerial orthophotographs from swisstopo (Federal Office of Topography). To regularly produce a revised inventory, based on the high-quality aerial images from swisstopo acquired at a three-year interval, the workload cannot be covered by GLAMOS (Glacier Monitoring Switzerland, www.glamos.ch) on its own. As part of the development of the new topographic landscape model of Switzerland (swissTLM3D), swisstopo introduced - based on requirements defined by GLAMOS - the object class "glaciers". This secures that Swiss glaciers are recurrently mapped based on high-resolution data on a long term. Swiss Glacier Inventories can therefore be derived by GLAMOS from the TLM object class "glaciers".The SGI2020 is the first glacier inventory produced by GLAMOS based on the new workflow and stands out with an unprecedented level of detail regarding glacier mapping. As the glacier-excerpt from the swisstopo TLM is a landcover dataset, produced according to guidelines for topographical purpose, it does not fit all glaciological requirements. Here, we present the necessary steps and adjustments to derive a new glacier inventory for the period 2013-2018 that fits all glaciological criteria. Furthermore, we compare the resulting dataset with former SGI's and pin down the major changes and differences emerging from different methodologies used. We particularly emphasize on problematic definitions of glacier boundaries related to snow coverage and/or supraglacial debris and provide updated results for glacier area changes in the Swiss Alps over the last decades.