A new semi-automatic approach for dividing glacier complexes into individual glaciers

Many glaciological and hydrological studies require outlines of individual glaciers rather than total ice cover. Here we develop a new semiautomatic algorithm that uses a digital elevation model (DEM) and outlines of glacier complexes to calculate the extents of individual glaciers. The algorithm first applies hydrological modeling tools to a modified DEM to calculate flowsheds. It then merges flowsheds that belong to individual glaciers using a distance-based approach, whose required empirical parameters are derived from the Juneau Icefield area in Alaska. In this region, 2% of ∼1300 glaciers were misclassified. The algorithm was validated on >25 000 km 2 of ice in other regions in Alaska and on >40 000 km 2 of ice in Arctic Canada, resulting in ∼2% and ∼3% misclassified glaciers, respectively. Results indicate that the algorithm is robust provided the DEM and the outlines are of good quality.