Abstract
Abstract. Despite their importance for sea-level rise, seasonal water availability, and as a source of geohazards, mountain glaciers are one of the few remaining subsystems of the global climate system for which no globally applicable, open source, community-driven model exists. Here we present the Open Global Glacier Model (OGGM), developed to provide a modular and open-source numerical model framework for simulating past and future change of any glacier in the world. The modeling chain comprises data downloading tools (glacier outlines, topography, climate, validation data), a preprocessing module, a mass-balance model, a distributed ice thickness estimation model, and an ice-flow model. The monthly mass balance is obtained from gridded climate data and a temperature index melt model. To our knowledge, OGGM is the first global model to explicitly simulate glacier dynamics: the model relies on the shallow-ice approximation to compute the depth-integrated flux of ice along multiple connected flow lines. In this paper, we describe and illustrate each processing step by applying the model to a selection of glaciers before running global simulations under idealized climate forcings. Even without an in-depth calibration, the model shows very realistic behavior. We are able to reproduce earlier estimates of global glacier volume by varying the ice dynamical parameters within a range of plausible values. At the same time, the increased complexity of OGGM compared to other prevalent global glacier models comes at a reasonable computational cost: several dozen glaciers can be simulated on a personal computer, whereas global simulations realized in a supercomputing environment take up to a few hours per century. Thanks to the modular framework, modules of various complexity can be added to the code base, which allows for new kinds of model intercomparison studies in a controlled environment. Future developments will add new physical processes to the model as well as automated calibration tools. Extensions or alternative parameterizations can be easily added by the community thanks to comprehensive documentation. OGGM spans a wide range of applications, from ice–climate interaction studies at millennial timescales to estimates of the contribution of glaciers to past and future sea-level change. It has the potential to become a self-sustained community-driven model for global and regional glacier evolution.
Highlights
Glaciers constitute natural low-pass filters of atmospheric variability
We present the results of a series of single glacier and global simulations demonstrating the model’s usage and potential
After the interpolation to the target grid, the topography is smoothed using a Gaussian filter with a radius of 250 m
Summary
Glaciers constitute natural low-pass filters of atmospheric variability. They allow people to directly perceive slow changes of the climate system, which would otherwise be masked by short-term noise in human perception. During the past few years, great progress has been made in methods to model glaciers globally (Radicand Hock, 2011, 2014; Giesen and Oerlemans, 2012, 2013; Marzeion et al, 2012a, b, 2014a, b; Huss and Hock, 2015) While these approaches yield consistent results at the global scale, all of them suffer from greater uncertainties at the regional and local scales. Great advances have been made in the global availability of data and methods relevant for glacier modeling, spanning glacier outlines (Pfeffer et al, 2014), automatized glacier centerline identification (e.g., Kienholz et al, 2014), bedrock inversion methods (e.g., Huss and Farinotti, 2012), and global topographic datasets (e.g., Farr et al, 2007) Taken together, these advances allow the ice dynamics of glaciers to be simulated at the global scale, provided that adequate modeling platforms are available. We will discuss the potential for future developments that could be conducted by any interested research team
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