Supraglacial Drainage Efficiency of the Greenland Ice Sheet Estimated From Remote Sensing and Climate Models

Supraglacial stream/river catchments drain large volumes of surface meltwater off the southwestern Greenland Ice Sheet surface. Previous studies note a strong seasonal evolution of their drainage density (D-d), a classic measure of drainage efficiency defined as open channel length per unit catchment area, but a direct correlation between D-d and surface meltwater runoff (R) has not been established. We use 27 high-resolution (similar to 0.5 m) satellite images to map seasonally evolving D-d for four GrIS supraglacial catchments, with elevations ranging from 1,100 m to 1,700 m. We find a positive linear correlation (r(2) = 0.70, p < 0.01) between D-d and simulations of runoff production from two climate models (MAR v3.11 and MERRA-2). Applying this R-D-d empirical relationship to climate model output enables parameterization of spatial and temporal changes in supraglacial drainage efficiency continuously throughout the melt season, although temporal and spatial skewness of D-d observations likely affects the application of this R-D-d relationship on crevasse fields and snow/firn surfaces. Incorporating this information into a simple surface routing model finds that high runoff leads to earlier, larger diurnal peaks of runoff transport on the ice surface, owing to increased D-d. This effect progressively declines from low (similar to 1,100 m) to high (similar to 1,700 m) elevation, causing a roughly order-of-magnitude reduction in diurnal runoff variability at the highest elevations relative to standard climate model output. Combining intermittent satellite D-d mapping with climate model output thus promises to improve characterization of supraglacial drainage efficiency to the benefit of supraglacial meltwater routing and subglacial hydrology models.

Automated summary

There is a positive correlation between supraglacial drainage efficiency (D-d) and surface meltwater runoff (R) on the southwestern Greenland Ice Sheet. High-resolution satellite images can be used to map the spatial and temporal changes in D-d throughout the melt season, improving the characterization of supraglacial drainage efficiency.