An ~1899 glacier inventory for Nordland, northern Norway, produced from historical maps

Glaciers depicted on old maps reveal their historical extents, prior to 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 the northern Norwegian county of Nordland 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 (LIA) 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 1,712 ± 291 km² in 1899. By 2000, total ice cover had decreased by 47 % (807 ± 137 km²) at a rate of 6 % 10a-1 (80 ± 14 km² 10a^-1). The approach presented in this research may serve as a blueprint for future studies intending to derive glacier inventories from historical maps.