Water Science and Technology; Earth-Surface Processes
Abstract :
[en] As surface melt is increasing on the Greenland Ice Sheet (GrIS), quantifying the retention capacity of the firn layer is critical to linking meltwater production to meltwater runoff. Firn-densification models have so far relied on empirical approaches to account for the percolation-refreezing process, and more physically based representations of liquid water flow might bring improvements to model performance. Here we implement three types of water percolation schemes into the Community Firn Model: the bucket approach, the Richards equation in a single domain and the Richards equation in a dual domain, which accounts for partitioning between matrix and fast preferential flow. We investigate their impact on firn densification at four locations on the GrIS and compare model results with observations. We find that for all of the flow schemes, significant discrepancies remain with respect to observed firn density, particularly the density variability in depth, and that inter-model differences are large (porosity of the upper 15m firn varies by up to 47%). The simple bucket scheme is as efficient in replicating observed density profiles as the single-domain Richards equation, and the most physically detailed dual-domain scheme does not necessarily reach best agreement with observed data. However, we find that the implementation of preferential flow simulates ice-layer formation more reliably and allows for deeper percolation. We also find that the firn model is more sensitive to the choice of densification scheme than to the choice of water percolation scheme. The disagreements with observations and the spread in model results demonstrate that progress towards an accurate description of water flow in firn is necessary. The numerous uncertainties about firn structure (e.g. grain size and shape, presence of ice layers) and about its hydraulic properties, as well as the one-dimensionality of firn models, render the implementation of physically based percolation schemes difficult. Additionally, the performance of firn models is still affected by the various effects affecting the densification process such as microstructural effects, wet snow metamorphism and temperature sensitivity when meltwater is present.
Disciplines :
Earth sciences & physical geography
Author, co-author :
Verjans, Vincent; Lancaster Environment Centre, Lancaster University, Lancaster, United Kingdom
Leeson, Amber A. ; Lancaster Environment Centre, Data Science Institute, Lancaster University, Lancaster, United Kingdom
Max Stevens, C.; Department of Earth and Space Sciences, University of Washington, Seattle, United States
MacFerrin, Michael ; Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, United States
Noël, Brice ; Université de Liège - ULiège > Département de géographie > Climatologie et Topoclimatologie ; Institute for Marine and Atmospheric Research Utrecht, Utrecht University, Utrecht, Netherlands
Van Den Broeke, Michiel R. ; Institute for Marine and Atmospheric Research Utrecht, Utrecht University, Utrecht, Netherlands
Language :
English
Title :
Development of physically based liquid water schemes for Greenland firn-densification models
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