Inter-comparison of surface meltwater routing models for the Greenland Ice Sheet and influence on subglacial effective pressures

• Main Authors: Yang, Kang, Sommers, Aleah, Andrews, Lauren C., Smith, Laurence C., Lu, Xin, Fettweis, Xavier, Li, Manchun
• Format: Text
• Language: English
• Published: 2019
• Subjects: Greenland; Ice Sheet
• Online Access: https://doi.org/10.5194/tc-2019-255; https://tc.copernicus.org/preprints/tc-2019-255/

Each summer, large volumes of surface meltwater flow over the Greenland Ice Sheet (GrIS) surface and drain through moulins to the ice sheet bed, impacting subglacial hydrology and ice flow dynamics. Runoff modulations, or routing delays due to ice surface conditions, thus propagate to englacial and subglacial hydrologic systems, requiring accurate assessment to correctly estimate subglacial effective pressures and short-term lags between climatological melt production and ice velocity. This study compares hourly supraglacial moulin discharge simulations from three surface meltwater routing models, the Synthetic Unit Hydrograph (SUH), Surface Routing and Lake Filling (SRLF), and Rescaled Width Function (RWF), for four internally drained catchments (IDCs) located on the southwestern GrIS surface. Using surface runoff from the MAR regional climate model (RCM), simulated values of surface meltwater transport velocity, flow length, total transport time, unit hydrograph, peak moulin discharge, and time to peak are compared among the three routing models. For each IDC, modeled moulin hydrographs are also input to the SHAKTI subglacial hydrologic model to simulate corresponding subglacial effective pressure variations in the vicinity of a single moulin. Two routing models requiring use of a digital elevation model (SRLF, RWF) are assessed for the impact of DEM spatial resolution on simulated moulin hydrographs. Results indicate SUH, SRLF, and RWF perform differently in simulating moulin peak discharge and time to peak, with RWF simulating slower, smaller peak moulin discharges than SUH or SRLF. SRLF routing is sensitive to DEM spatial resolution, whereas RWF is not. Seasonal evolution of supraglacial stream/river networks is readily accommodated by RWF but not SUH or SRLF. In general, all three models are superior to simply using RCM output without routing, but significant differences among them are found. This variability among surface meltwater routing models is reflected in SHAKTI subglacial hydrology simulations, yielding differing diurnal effective pressure fluctuations.