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

Abstract

Abstract. We present BrAHMs (BAsal Hydrology Model): a 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 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 Courant–Friedrichs–Lewy (CFL) condition is met for numerical stability. The 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, displays the arborescent configuration expected of Röthlisberger channels. The model is also shown to be stable under high-frequency oscillatory meltwater inputs.

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

“…Ritz et al, 2015;Peano et al, 2017). GRISLI has participated in several intercomparison exercises (Calov et al, 2010;Edwards et al, 2014;Koenig et al, 2015;Goelzer et al, 2017) and has been coupled to climate models of various complexities (e.g. Philippon et al, 2006;Roche et al, 2014;Le clec'h et al, 2018).…”

Surging of a Hudson Strait-scale ice stream: subglacial hydrology matters but the process details mostly do not

“…In the linked-cavity system, cavities within the base of the ice open up as basal ice flows over and around bed protrusions -fast flow and larger objects beget larger cavities (Kamb, 1987). As cavities grow larger and numerous they form a connected network linked through smaller orifices giving a tortuous drainage network.…”

Surging of a Hudson Strait Scale Ice Stream: Subglacial hydrology matters but the process details don't

“…The subglacial hydrology model -BraHms2.0 -is an extensive update to v1.0 (Kavanagh and Tarasov, 2018), which involves the addition of linked-cavity and leaky bucket systems, an updated generalized grid, modified convergence criteria, modified flux limiter, and code restructuring. This model uses a finite volume discretization with a staggered Arkawa C grid (fluxes at interfaces).…”

“…As subglacial water is routed down hydraulic gradient, minima in hydraulic potential are filled and excess water carried further down gradient until either no water remains or the drainage chain reaches the margin and the remaining water leaves the system. This routing scheme is further discussed in Kavanagh and Tarasov (2018).…”

“…CC BY 4.0 License. the initial time step followed by a leap-frog trapezoidal predictor corrector method (Kavanagh and Tarasov, 2018). To avoid time splitting, Heun's method is called after every 10 leap frog steps (varying the number of leap frog steps had little effect on the solution in tests).…”