ACINN Graduate Seminar - SS 2026

2026-06-24 at 12:00 (on-line and on-site) in the seminar room

Firn Hydrological Processes in Greenland's Percolation Zone: How Much Melts, Refreezes, and Runs Off?

Falk Oraschewski

Department of Glaciology and Climate, Geological Survey of Denmark and Greenland (GEUS)

 

Surface melting and runoff accounts for about half of the Greenland ice sheet mass loss. This atmospheric-forced contribution has increased over recent decades and is projected to enhance further as climate warming intensifies. A key component in Greenland's hydrological system is the percolation zone, describing the lower elevation bands of the accumulation zone, where the meltwater generated during summer can percolate and partially refreeze in the porous snow and firn that accumulated over winter. This refreezing buffers immediate surface mass loss but reduces the future buffering capacity, controlling the inland migration of the runoff limit and total future runoff. However, due to a lack of in situ observations, parametrizations of these firn hydrological processes in regional climate models (RCMs) remain underconstrained, resulting in significant uncertainties in future mass balance projections.

Here, we present a novel approach to continuously monitor liquid water in firn throughout the melt season. Multi-year observations (2023-2026) were acquired using the Autonomous phase-sensitive radio echo sounder (ApRES) at four GC-NET automatic weather station sites across Greenland’s percolation zone (KAN_U, DYE-2, Crawford Point and Camp Century). Through a joint analysis of these data with our GEUS firn model, we can constrain how much meltwater is generated, refreezes and, particularly, runs off. A comparison with runoff simulations from three RCMs highlights deficiencies in their runoff parametrizations in terms of the timing, location, and magnitude of runoff. Our results demonstrate the potential of ApRES firn water monitoring to improve RCM representations of Greenland's percolation zone and narrow uncertainties in Greenland ice sheet mass balance projections.

 

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