Abstract
Abstract. In this study, we assess glacier area and length changes in mainland Norway from repeat Landsat TM/ETM+-derived inventories and digitized topographic maps. The multi-temporal glacier inventory consists of glacier outlines from three time ranges: 1947 to 1985 (GIn50), 1988 to 1997 (GI1990), and 1999 to 2006 (GI2000). For the northernmost regions, we include an additional inventory (GI1900) based on historic maps surveyed between 1895 and 1907. Area and length changes are assessed per glacier unit, 36 subregions, and for three main parts of Norway: southern, central, and northern. The results show a decrease in the glacierized area from 2994 km2 in GIn50 to 2668 km2 in GI2000 (total 2722 glacier units), corresponding to an area reduction of −326 km2, or −11% of the initial GIn50 area. The average length change for the full epoch (within GIn50 and GI2000) is −240 m. Overall, the comparison reveals both area and length reductions as general patterns, even though some glaciers have advanced. The three northernmost subregions show the highest retreat rates, whereas the central part of Norway shows the lowest change rates. Glacier area and length changes indicate that glaciers in maritime areas in southern Norway have retreated more than glaciers in the interior, and glaciers in the north have retreated more than southern glaciers. These observed spatial trends in glacier change are related to a combination of several factors such as glacier geometry, elevation, and continentality, especially in southern Norway.
Highlights
Glaciers are key indicators of climate change, making their monitoring important (e.g., Vaughan et al, 2013)
Comparison of our glacier length changes with cumulative field data from NVE for 12 selected glaciers shows a mean deviation of 89 m (< 4 %) for the full epoch (Table 4), which indicates that the satellite- and map-derived glacier length changes are in agreement for groups of glaciers, the deviation can be relatively large for individual glaciers
We present our data of glacier area changes as absolute, relative (%), and normalized values for different time periods in order to provide a thorough presentation of the data
Summary
Glaciers are key indicators of climate change, making their monitoring important (e.g., Vaughan et al, 2013). The most recent satellite-derived glacier inventory of Norway is based on Landsat TM/ETM+ (Andreassen et al, 2012b) It uses a GIS-based approach and is compiled following the Global Land Ice Measurements from Space (GLIMS) guidelines (Kargel et al, 2005; Racoviteanu et al, 2010). This data set is a highly detailed digital baseline product ideal for glacier area and length change assessments (Andreassen et al, 2008; Paul and Andreassen, 2009; Paul et al, 2011). Concerning the multi-spectral band ratio technique, we demonstrate that mapped glacier areas are sensitive to small variations in the chosen ratio thresholds
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