Journal Article

Direct measurements of meltwater runoff on the Greenland ice sheet surface

Overstreet, Brandon T., Box, Jason E., Cooper, Matthew G., Rennermalm, Åsa K., Jeyaratnam, Jeyavinoth, Langen, Peter L., Ryan, Jonathan C., Tedesco, Marco, Hubbard, Alun, Yang, Kang, Smith, Laurence C., Behar, Alberto E., van de Berg, Willem Jan, Jenner, Brittany A., Willis, Michael J., Pitcher, Lincoln H, Gleason, Colin J., van As, Dirk, Noël, Brice, Cullather, Richard I., van den Broeke, Michiel R., Zhao, Bin, Chu, Vena W.

2017

Overview

Meltwater runoff from the Greenland ice sheet surface influences surface mass balance (SMB), ice dynamics, and global sea level rise, but is estimated with climate models and thus difficult to validate. We present a way to measure ice surface runoff directly, from hourly in situ supraglacial river discharge measurements and simultaneous high-resolution satellite/drone remote sensing of upstream fluvial catchment area. A first 72-h trial for a 63.1-km² moulin-terminating internally drained catchment (IDC) on Greenland’s midelevation (1,207–1,381 m above sea level) ablation zone is compared with melt and runoff simulations from HIRHAM5, MAR3.6, RACMO2.3, MERRA-2, and SEB climate/SMB models. Current models cannot reproduce peak discharges or timing of runoff entering moulins but are improved using synthetic unit hydrograph (SUH) theory. Retroactive SUH applications to two older field studies reproduce their findings, signifying that remotely sensed IDC area, shape, and supraglacial river length are useful for predicting delays in peak runoff delivery to moulins. Applying SUH to HIRHAM5, MAR3.6, and RACMO2.3 gridded melt products for 799 surrounding IDCs suggests their terminal moulins receive lower peak discharges, less diurnal variability, and asynchronous runoff timing relative to climate/SMB model output alone. Conversely, large IDCs produce high moulin discharges, even at high elevations where melt rates are low. During this particular field experiment, models overestimated runoff by +21 to +58%, linked to overestimated surface ablation and possible meltwater retention in bare, porous, low-density ice. Direct measurements of ice surface runoff will improve climate/SMB models, and incorporating remotely sensed IDCs will aid coupling of SMB with ice dynamics and subglacial systems.

• Publisher: National Academy of Sciences
• Subject: Ablation / Catchment areas / Climate / Climate models / Computer simulation / Diurnal / Earth sciences & physical geography / Earth, Atmospheric, and Planetary Sciences / fluvial catchment / Ice / ice sheet meltwater runoff / Meltwater / Multidisciplinary / Physical Sciences / Physical, chemical, mathematical & earth Sciences / Physique, chimie, mathématiques & sciences de la terre / PNAS Plus / Remote sensing / River discharge / River flow / Rivers / Runoff / Sciences de la terre & géographie physique / Sea level / Sea level rise / Simulation / surface mass balance / Surface runoff / surface water hydrology / Unit hydrographs / Water discharge