A dynamic continental runoff routing model applied to the last Northern Hemisphere deglaciation

Abstract

We describe and evaluate a dynamical continental runoff routing model forthe Northern Hemisphere that calculates the runoff pathways in response totopographic modifications due to changes in ice thickness and isostaticadjustment. The algorithm is based on the steepest gradient method and takesas simplifying assumption that depressions are filled at all times and waterdrains through the lowest outlet points. It also considers changes in waterstorage and lake drainage in post-processing mode that become important inthe presence of large ice dammed proglacial lakes. Although applicable toother scenarios as well, the model was conceived to study the routing offreshwater fluxes during the last Northern Hemisphere deglaciation. For thatspecific application we simulated the Northern Hemisphere ice sheets with anexisting 3-D thermomechanical ice sheet model, which calculates changes intopography due to changes in ice cover and isostatic adjustment, as well asthe evolution of freshwater fluxes resulting from surface ablation, icebergcalving and basal melt. The continental runoff model takes this input,calculates the drainage pathways and routes the freshwater fluxes to thesurface grid points of an existing ocean model. This results in a chronologyof temporally and spatially varying freshwater fluxes from the Last GlacialMaximum to the present day. We analyse the dependence of the runoff routingto grid resolution and parameters of the isostatic adjustment module of theice sheet model. © Author(s) 2012. CC Attribution 3.0 License.