Preprints
https://doi.org/10.5194/tc-2020-314
https://doi.org/10.5194/tc-2020-314

  27 Nov 2020

27 Nov 2020

Review status: this preprint is currently under review for the journal TC.

Seasonal Variability in In-situ Supraglacial Streamflow and Drivers in Southwest Greenland in 2016

Rohi Muthyala1, Asa K. Rennermalm1, Sasha Z. Leidman1, Matthew G. Cooper2, Sarah W. Cooley3,4, Laurence C. Smith3,4, and Dirk van As5 Rohi Muthyala et al.
  • 1Department of Geography, Rutgers, The State University of New Jersey, New Brunswick, NJ, 08901, USA
  • 2Atmospheric Sciences and Global Change Division, Pacific Northwest National Laboratory, Richland, WA, 99354, USA
  • 3Institute at Brown for Environment and Society, Brown University, Providence, RI, 02912, USA
  • 4Department of Earth, Environmental, and Planetary Sciences, Brown University, Providence, RI, 02912, USA
  • 5Geological Survey of Denmark and Greenland, Øster Voldgade 10, 1350 Copenhagen, Denmark

Abstract. Greenland ice sheet surface runoff is evacuated through supraglacial stream networks, which influence surface mass balance as well as ice dynamics. However, in-situ observations of meltwater discharge through these stream networks are rare. In this study, we present 46 discharge measurements and continuous water level measurements for 62 days spanning 13 June to 13 August 2016 for a 0.6 km2 supraglacial stream catchment in southwest Greenland. The result is an unprecedented long record of supraglacial discharge capturing both diurnal and seasonal variability. By comparing in situ hydraulic geometry parameters with previous studies, we find that significant heterogeneity exists such that estimating stream discharge using these parameters over ungauged supraglacial catchments could lead to substantial errors. A comparison of surface energy fluxes to stream discharge reveals shortwave radiation as the primary driver of melting (78 % of melt energy). However, during high melt episodes, the shortwave only contributes to 50 % of melt energy. Instead, the relative contribution of longwave radiation, sensible and latent heat fluxes to overall melt increases by 16.5 %, 4 %, and 7 % respectively. Our data also show a seasonal variation in the timing of daily maximum discharge during clear sky days, shifting from 16:00 local time (i.e., 2.75 hours after solar noon) in late June to 14:00 in late July, then rapidly returns to 16:00 in early August coincident with an abrupt drop in air temperature. These changes in peak daily flow timing can be attributed to a changing effective catchment area, resulting in a smaller stream network supplying water to the outlet at the end of the season throughout the melt season. Further work is needed to uncover how widespread rapid shift in the timing of peak discharge is across Greenland supraglacial streams, and thus their potential impact on meltwater delivery to the subglacial system and ice dynamics.

Rohi Muthyala et al.

 
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Rohi Muthyala et al.

Rohi Muthyala et al.

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Short summary
In-situ measurements of meltwater discharge through supraglacial stream networks are rare. The unprecedented long record of discharge captures diurnal and seasonal variability. Two major findings are: first, seasonal variability in the timing of peak discharge that could impact meltwater delivery in the subglacial system. Second, though the primary driver of stream discharge is shortwave radiation, longwave radiation and turbulent heat fluxes play a major role during high melt episodes.