An ~1899 glacier inventory for Nordland, northern Norway, produced from historical maps. Issue 256 (6th April 2020) - Weber, Paul
Abstract: Glaciers depicted on old maps reveal their historical extents, before the advent of aerial and satellite remote sensing. Digital glacier inventories produced from these maps can be employed in assessments of centennial-scale glacier change. This study reconstructs the ~1899 (covering the period 1882–1916) glacier extent in Nordland, northern Norway, from historical gradteigskart maps, with an emphasis on examining the accuracy of the mapped glaciers. Glacier outlines were digitised from georectified scans of the analogue maps in a raster graphics editor and were subsequently inventoried in a GIS. The accuracy of the historical glacier extent was established from written descriptions and landscape photographs created during the original field surveys, and further validated against independent glacier outlines of (1) the maximum Little Ice Age extent derived from geomorphological evidence, and (2) the 1945 extent derived from vertical aerial photographs. An overall uncertainty of ±17% is associated with our inventory. Nordland's glaciers covered an area of 1712 ± 291 km 2 in 1899. By 2000, total ice cover had decreased by 47% (807 ± 137 km 2 ) at a rate of 6% 10 a −1 (80 ± 14 km 2 10 a −1 ). The approach presented here may serve as a blueprint for future studies intending to derive glacier inventories from historical maps.