Annual Terminus Prediction Errors for Greenland Glaciers from Calving Laws and Melt Parameterizations

Many calving laws have been proposed leading to a need to characterize the ability of these laws to predict terminus movement across years. The influence of terminus change on glacier discharge makes this an important source of uncertainty for multi-decadal sea level rise prediction from ice sheet models. Here, we develop a workflow to tune calving laws and then calculate error in predicted terminus positions based on Greenland Ice Sheet Mapping Project (GrIMP) surface velocity data sets compiled from Sentinel, Landsat, TerraSAR-X, TanDEM-X, and COSMO-SkyMed satellites as well as digital elevation models (DEMs) from ASTER mission and ArcticDEM data.  Greenland glaciers with available data are used to test the height above flotation, fraction above flotation, crevasse depth criterion, von Mises criterion, and surface stress maximum calving laws over a multi-year period. Several versions of the crevasse depth law based on stress input are tested providing insight into the law’s dependence on stress calculation. This dependence is important as the crevasse depth law has been recommended by calving law comparison but has been implemented with various stress calculations to work with three-dimensional stress fields. The terminus melt parameterization used in the Ice Sheet Model Intercomparison Project for CMIP6 standard experiments is included as reference to show the degree to which calving laws are needed to accurately model retreat for future model intercomparison efforts. While testing calving laws independent of an ice sheet model will not provide insight into all the challenges of calving implementation for ice-sheet-wide studies, this remote-sensing based workflow can rapidly test calving laws’ terminus prediction errors. With the availability of monthly-averaged velocity data sets and frequent instantaneous DEMs, this method will allow for analysis of calving law success on many regimes of multi-year glacier movement.