Abstract
Abstract. Recent work has identified complex perennial supraglacial stream and river networks in areas of the Greenland Ice Sheet (GrIS) ablation zone. Current surface mass balance (SMB) models appear to overestimate meltwater runoff in these networks compared to in-channel measurements of supraglacial discharge. Here, we constrain SMB models using the hillslope river routing model (HRR), a spatially explicit flow routing model used in terrestrial hydrology, in a 63 km2 supraglacial river catchment in southwest Greenland. HRR conserves water mass and momentum and explicitly accounts for hillslope routing (i.e., flow over ice and/or firn on the GrIS), and we produce hourly flows for nearly 10 000 channels given inputs of an ice surface digital elevation model (DEM), a remotely sensed supraglacial channel network, SMB-modeled runoff, and an in situ discharge dataset used for calibration. Model calibration yields a Nash–Sutcliffe efficiency as high as 0.92 and physically realistic parameters. We confirm earlier assertions that SMB runoff exceeds the conserved mass of water measured in this catchment (by 12 %–59 %) and that large channels do not dewater overnight despite a diurnal shutdown of SMB runoff production. We further test hillslope routing and network density controls on channel discharge and conclude that explicitly including hillslope flow and routing runoff through a realistic fine-channel network (as opposed to excluding hillslope flow and using a coarse-channel network) produces the most accurate results. Modeling complex surface water processes is thus both possible and necessary to accurately simulate the timing and magnitude of supraglacial channel flows, and we highlight a need for additional in situ discharge datasets to better calibrate and apply this method elsewhere on the ice sheet.
Highlights
The study of supraglacial streams and rivers atop the Greenland Ice Sheet (GrIS) is an emerging subfield with implications for the physical understanding of ice sheet subglacial hydrologic systems, ice motion, and sea level rise (IrvineFynn et al, 2011; Rennermalm et al, 2013; Chu, 2014; Flowers, 2018; Pitcher and Smith, 2019)
Gleason et al.: Hourly surface meltwater routing for a Greenlandic supraglacial catchment melts, meltwater that is not evaporated, stored, or refrozen moves through what is understood to be a complex perennial hydrologic system distinct from terrestrial hydrology (Yang et al, 2016; Pitcher and Smith, 2019)
Cision due to frictional heating of the channels, but without including a radiation budget and ice property data we could not model how the stream network changes in time nor satisfactorily model this additional meltwater with commensurate sophistication to the surface mass balance (SMB) runoff forcing. We model these network snapshots with hillslope river routing model (HRR) loosely coupled with SMB runoff, which is reasonable for our 1-month experiment (Sect. 3.3.1)
Summary
The study of supraglacial streams and rivers atop the Greenland Ice Sheet (GrIS) is an emerging subfield with implications for the physical understanding of ice sheet subglacial hydrologic systems, ice motion, and sea level rise (IrvineFynn et al, 2011; Rennermalm et al, 2013; Chu, 2014; Flowers, 2018; Pitcher and Smith, 2019). Recent advances in mapping (Lampkin and VanDerberg, 2014; Rippin et al, 2015; Smith et al, 2015, 2017; Yang and Smith, 2016), modeling (Banwell et al, 2012, 2016; Clason et al, 2015; Karlstrom and Yang, 2016; Yang et al, 2018) and measuring (McGrath et al, 2011; Legleiter et al, 2014; Gleason et al, 2016; Smith et al, 2017) supraglacial channel networks have revealed numerous similarities to terrestrial watersheds, but their scale and remoteness have limited the number of field studies
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call