Inventory of Norwegian glaciers

Abstract

This inventory of the glaciers in mainland Norway in book form consists of two parts: a text section with background information, description of the methods used and main results, and a map and table section that includes all identified glaciers. To derive this new inventory satellite images from the Landsat sensors from the period 1999-2006 were analysed. The sui- tability of a semi-automatic band-ratio method was first applied to map glaciers in a test region in Jotunheimen, before the method was applied to map all glaciers in Norway. All automatically mapped snow and ice polygons were visually inspected using composites of satellite image bands, digital topographic maps and orthophotos where available. The po- lygons were manually classified as ‘glaciers’, ‘possible snowfields’ or ‘snow’. Manual corrections for debris cover, glacier- lake interfaces, clouds or cast shadow were made where necessary. All polygons to be included in this new inventory were assigned a unique ID. Glacier complexes were divided into glacier units using drainage divides. Many smaller polygons which had been classified as possible snowfields due to size, shape or due to uncertainty regarding ice content were not as- signed IDs and were therefore not included in this inventory book. Glacier names were assigned both to individual glacier units and to glacier complexes. To be consistent we used the spelling from the digital N50 topographic maps produced by the Norwegian Mapping Authority, although in some cases these are different to those used in the previous inventories. In total 2534 glaciers (3143 glacier units) were defined in the new inventory. Of these 1252 glaciers (1575 glacier units) were in southern Norway and 1282 (1568 glacier units) were in northern Norway. The total glacier area is 2692 km2 ± 81 km2 (using ± 3% as uncertainty), the larger part, 1523 km2 (57%), is located in southern Norway, and 1169 km2 (43%) in northern Norway. In addition, about 400 polygons classified as ‘possible snowfield’, and without glacier ID, amount to 24 km2. The total glacier area including these polygons is 2716 km2. Glaciers and perennial snowfields in Norway thus cover about 0.7% of the land area in mainland Norway. The number of glaciers included in this inventory is nearly 57% larger compared to the 1627 glaciers reported in the pre- vious inventories of Norway (Atlas 88 and Atlas 73). The increase in number of glaciers is mainly due to inclusion of many small entities that were not included in the old inventories. The difference in numbers can be explained by the change in the methods applied to map glaciers. In the old inventories glaciers were manually drawn, whereas in this Landsat-deri- ved inventory almost all snow and ice was automatically mapped, except debris covered parts and bodies in cast shadow. Some of the smaller entities we included in this new inventory are perennial ice masses, and some may even be seasonal snow where snow conditions were adverse for mapping. In particular some of the scenes used for northern Norway have more seasonal snow and may thus overestimate glacier extents. The new digital glacier outlines of Norway have been used to assess glaciers changes by comparison with topographic maps in selected regions. Results show a large variability in the regions studied so far, ranging from –1% in the Svartisen region to –28% for the five northernmost ice caps.