Articles | Volume 10, issue 2
20 Apr 2018
 | 20 Apr 2018

Historical glacier outlines from digitized topographic maps of the Swiss Alps

Daphné Freudiger, David Mennekes, Jan Seibert, and Markus Weiler

Abstract. Since the end of the Little Ice Age around 1850, the total glacier area of the central European Alps has considerably decreased. In order to understand the changes in glacier coverage at various scales and to model past and future streamflow accurately, long-term and large-scale datasets of glacier outlines are needed. To fill the gap between the morphologically reconstructed glacier outlines from the moraine extent corresponding to the time period around 1850 and the first complete dataset of glacier areas in the Swiss Alps from aerial photographs in 1973, glacier areas from 80 sheets of a historical topographic map (the Siegfried map) were manually digitized for the publication years 1878–1918 (further called first period, with most sheets being published around 1900) and 1917–1944 (further called second period, with most sheets being published around 1935). The accuracy of the digitized glacier areas was then assessed through a two-step validation process: the data were (1) visually and (2) quantitatively compared to glacier area datasets of the years 1850, 1973, 2003, and 2010, which were derived from different sources, at the large scale, basin scale, and locally. The validation showed that at least 70 % of the digitized glaciers were comparable to the outlines from the other datasets and were therefore plausible. Furthermore, the inaccuracy of the manual digitization was found to be less than 5 %. The presented datasets of glacier outlines for the first and second periods are a valuable source of information for long-term glacier mass balance or hydrological modelling in glacierized basins. The uncertainty of the historical topographic maps should be considered during the interpretation of the results. The datasets can be downloaded from the FreiDok plus data repository (,

Short summary
To understand glacier changes in the Swiss Alps at the large scale, long-term datasets are needed. To fill the gap between the existing glacier inventories of the Swiss Alps between 1850 and 1973, we digitized glacier outlines from topographic historical maps of Switzerland for the time periods ca. 1900 and ca. 1935. We found that > 88 % of the digitized glacier area was plausible compared to four inventories. The presented dataset is therefore valuable information for long-term glacier studies.