Theoretical equilibrium-line altitudes and glacier buildup sensitivity in southern Norway based on meteorological data in a geographical information system

Three equations derived from a close exponential glacier-climate relationship at the equilibrium-linealtitude (ELA) of Norwegian glaciers have been utilized and implemented in a geographical information system(GIS). The first equation enables calculation of the minimum altitude of areas climatically suited for glacierformation at present, and is termed the altitude of instantaneous glacierization (AIG). Equation (2) is basedon the ‘principle of terrain adaptation’, enabling quantification of the glacial buildup sensitivity (GBS) in anarea. The third equation calculates the theoretical climatic (instrumental) temperature-precipitation ELA (CTPELA)in presently non-glaciated areas by combining GBS with terrain altitude. The presented approach isprimarily intended for palaeoclimatic analyses of former glacial records, and is tested here based on a plot of122 temperature stations and 197 precipitation stations during the climate normal period 1961–1990 which hasbeen recalculated to sea level using empirical vertical climatic gradients. These data were interpolated in the GISusing an ‘inverse square interpolation’ routine. Subsequently, the interpolated climatic data were recalculated tothe terrain surface using vertical climatic gradients and a digital elevation model (DEM) of southern Norway(resolution 5 3 5 degree minutes/c. 1 km2). The present glacier distribution in southern Norway is reproducedin great detail, and maps showing the modern GBS and CTP-ELA in non-glacierized areas of southern Norwayare presented. Based on the GBS analysis, four scenarios with ELA depressions of 150 m (average ‘Little IceAge’ conditions), 500 m (average coastal Younger Dryas conditions), 1000 m (suggested late Weichselianmaximum coastal conditions) and 1500 m are shown