The length of the world's glaciers – a new approach for the global calculation of center lines

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 lowquality 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.

Derivation and analysis of a complete modern-date glacier inventory for Alaska and northwest Canada

“…Our derived log-log relationship for all glaciers (1:55A 0:647 ) is slightly steeper than the relationship 1:59A 0:606 of Machguth and Huss (2014), who used a different method of deriving the glacier lengths and a lower minimal size threshold. The two fits intersect at 1.85 km 2 , with greater lengths of the Machguth and Huss (2014) approach below the intersection. In our case, one single log-log fit tends to overestimate the length of the largest glaciers.…”

“…Coefficient and exponent are chosen to obtain 20% length errors at 0.1 km 2 and 5% errors at 10 km 2 (resulting in 2.5% and 1.25% errors at 100 and 1000 km 2 , respectively). This equation does not account for possible systematic differences which may occur towards smaller size classes, as indicated by Machguth and Huss (2014). Also, it does not account for varying DEM quality, which can locally reduce the accuracy of the derived center-line lengths.…”

“…This supports the choice of a conservative error correlation scenario for the regional error estimate (Table 3). Machguth and Huss (2014) derived glacier lengths for Alaska using the same outlines and DEM as this study, but a different method. As part of their study, they compared the center-line lengths obtained from the two methods.…”

The New Swiss Glacier Inventory SGI2010: Relevance of Using High-Resolution Source Data in Areas Dominated by Very Small Glaciers

“…Glacier length (parameter 5) was measured along an automatically derived center line (cf. Machguth and Huss, 2014). The entire data set is available over the Global Land Ice Measurements from Space (GLIMS) database.…”

Fusion of Multi-Source Satellite Data and DEMs to Create a New Glacier Inventory for Novaya Zemlya

“…Glacier outlines are a key dataset for analysing glacier fluctuations (changes in length [1], area [2,3] and volume/mass [4]), determining their characteristics (e.g., [1,5]), run-off contribution [6] or future behaviour [7]. In addition, they allow spatially constrained calculations of glacier specific products such as flow velocities and stable terrain for accuracy assessment of glacier volume changes derived from two digital elevation models (DEMs) [8].…”