Abstract
Abstract. Glacier length is an important measure of glacier geometry. Nevertheless, global glacier inventories are mostly lacking length data. Only recently semi-automated approaches to measure glacier length have been developed and applied regionally. Here we present a first global assessment of glacier length using an automated method that relies on glacier surface slope, distance to the glacier margins and a set of trade-off functions. The method is developed for East Greenland, evaluated for East Greenland as well as for Alaska and eventually applied to all ~ 200 000 glaciers around the globe. The evaluation highlights accurately calculated glacier length where digital elevation model (DEM) quality is high (East Greenland) and limited accuracy on low-quality DEMs (parts of Alaska). Measured length of very small glaciers is subject to a certain level of ambiguity. The global calculation shows that only about 1.5% of all glaciers are longer than 10 km, with Bering Glacier (Alaska/Canada) being the longest glacier in the world at a length of 196 km. Based on the output of our algorithm we derive global and regional area–length scaling laws. Differences among regional scaling parameters appear to be related to characteristics of topography and glacier mass balance. The present study adds glacier length as a key parameter to global glacier inventories. Global and regional scaling laws might prove beneficial in conceptual glacier models.
Highlights
Glacier length is one of the central measures representing the geometry of glaciers
By applying the above method to the entire global data set of glacier outlines and digital elevation model (DEM), we evaluated the length and center lines of all roughly 200 000 glaciers around the globe
Based on our data we investigate the relationship of glacier length and glacier area and calculate global and regional scaling laws
Summary
Glacier length is one of the central measures representing the geometry of glaciers. Changes in climate have a delayed but very clear impact on glacier length, and the advance or retreat of glaciers is frequently used to communicate observed changes to a broader public. Despite being scientifically relevant and easy to communicate, glacier length is difficult to define and has been measured only for a relatively small number of glaciers worldwide (Cogley, 2009; Paul et al, 2009; Leclercq et al, 2014). Several authors have defined glacier length as the length of the longest flow line of a glacier (e.g., Nussbaumer et al, 2007; Paul et al, 2009; Leclercq et al, 2012). Such a concept is reasonable because of linking length to glacier flow, one of the basic processes controlling the geometry of glaciers. Glacier length as a surface measure can only be linked indirectly to the threedimensional process of glacier flow
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