Capturing Runoff‐Driven Seasonal Velocity Variations of Fast‐Flowing Outlet Glaciers in Coupled Ice‐Hydrology Simulations

Abstract The seasonal evolution of the subglacial drainage system is a critical control on velocity variations of Greenland marine‐terminating glaciers. Yet numerical models struggle to reproduce observed seasonal behavior, because fast flow suppresses channelization in subglacial hydrology models. We simulate the full spectrum of runoff‐driven velocity variations, including the seasonal velocity pattern observed on many marine‐terminating outlet glaciers: speed‐up in the early melt season followed by a slowdown below winter values in late‐summer. This behavior arises by fully coupling hydrology and ice flow, using basal melt rates as predicted by and consistent with the coupled model, enhancing closure rates of subglacial cavities, and assuming laminar flow with low sheet conductivity. Together, these modifications promote channelization beneath fast‐flowing glaciers, which has previously been elusive.