BrAHMs V1.0: A fast, physically-based subglacial hydrology model for continental-scale application

Abstract

Abstract. We present BrAHMs (BAsal Hydrology Model): a new physically-based basal hydrology model which represents water flow using Darcian flow in the distributed drainage regime and a fast down-gradient solver in the channelized regime.Switching from distributed to channelized drainage occurs when appropriate flow conditions are met. The model is designed for long-term integrations of continental ice sheets. The Darcian flow is simulated with a robust combination of the Heun and 5 leapfrog-trapezoidal predictor-corrector schemes. These numerical schemes are applied to a set of flux-conserving equations cast over a staggered grid with water thickness at the centres and fluxes defined at the interface. Basal conditions (e.g. till thickness, hydraulic conductivity) are parameterized so the model is adaptable to a variety of ice sheets. Given the intended scales, basal water pressure is limited to ice overburden pressure, and dynamic time-stepping is used to ensure that the CFL condition is met for numerical stability. 10The model is validated with a synthetic ice sheet geometry and different bed topographies to test basic water flow properties and mass conservation. Synthetic ice sheet tests show that the model behaves as expected with water flowing down-gradient, forming lakes in a potential well or reaching a terminus and exiting the ice sheet. Channel formation occurs periodically over different sections of the ice sheet and, when extensive, display the arborescent configuration expected of Röthlisberger Channels. 15

The GRISLI ice sheet model (version 2.0): calibration and validation for multi-millennial changes of the Antarctic ice sheet

“…To progress further on this topic, the implementation of a new basal hydrology model relying on explicit routing scheme (e.g. Kavanagh and Tarasov, 2017) would allow to avoid relaxed numerical solutions based on effective pressure. This could introduce fast basal water changes that are currently ignored and, ultimately, could yield ice streams abrupt speed-up or slow-down.…”

BrAHMs V1.0: a fast, physically based subglacial hydrology model for continental-scale application

“…Code availability. Basal hydrology code with validation drivers is freely available at http://doi.org/10.5281/zenodo.1230046 (Kavanagh and Tarasov, 2018).…”