Modeling large‐scale landform evolution with a stream power law for glacial erosion (OpenLEM v37): benchmarking experiments against a more process-based description of ice flow (iSOSIA v3.4.3)

Abstract. Following the tradition of modeling fluvial landscape evolution, a novel approach describing glacial erosion based on an empirical stream power law was proposed. This approach differs substantially from well-established process-based models applied to describe glacial erosion in mountain landscapes. Outstanding computational performance but a number of potential limitations compared to process-based models requires extensive testing to evaluate the applicability of this novel approach. In this study, we test the validity of the glacial stream power law and its implementation into a 2-D landform evolution model (OpenLEM) by benchmarking it against a state of the art surface process model based on the integrated second-order shallow-ice approximation (iSOSIA). Despite completely different approaches, OpenLEM and iSOSIA predict similar ice flow patterns and erosion rates for a wide range of climatic conditions without re-adjusting a set of calibrated parameters. This parameter set is valid for full glacial conditions where the entire precipitation is converted to ice but also for an altitude-dependent glacier mass balance as characteristic for most glaciated mountain ranges on Earth. In both models characteristic glacial features, such as overdeepenings, hanging valleys and steps at confluences emerge roughly at the same locations, resulting in a consistent altitude-dependent adjustment of channel slope and relief. Compared to iSOSIA, however, distinctly higher erosion rates occur in OpenLEM at valley flanks during the initial phase of the fluvial to glacial transition. This is mainly due to the simplified description of glacier width and ice surface in OpenLEM. In this respect, we found that the glacial stream power approach cannot replace process-based models such as iSOSIA but is complementary to them by addressing research questions that could not previously be answered due to a lack of computational efficiency. The implementation of the glacial stream power law is primarily suitable for large-scale simulations investigating the evolution of mountain topography in the interplay of tectonics and climate. As coupling glacial and fluvial erosion with sediment transport shows nearly the same computational efficiency as its purely fluvial counterpart, mountain-range-scale simulations at high spatial resolution are not exclusively restricted to the fluvial domain anymore, and a series of exciting research questions can be addressed by this novel approach.