This project will study Greenlandic Rivers as integrated signals of a rapidly changing Arctic hydrological cycle. Observed increased rates of melt on the Greenland Ice Sheet (GrIS) are expected to have a profound impact on the runoff of numerous rivers draining the ice sheet margin. However, there are few observational records of water discharge of Greenlandic Rivers, or any other observations to constrain runoff to systematically assess the freshwater drained to the ocean. The researchers will use an innovative methodology to infer river discharges around Greenland from the characteristics of river plumes draining into the fjords. River plumes are prominently visible on remote-sensing imagery, and their dimensions and reflectance characteristics can be mapped on a daily-weekly basis over the length of the MODIS satellite record, which will amount to a detailed reconstruction of 10+ years. Plume characteristics are related to sediment concentration patterns and sediment removal rates by empirical transfer functions, which will be validated against 4 years of field data. River plumes are typically controlled by incoming river discharge and sediment load. Inverted process-based numerical model of river plumes in fjords use the mapped plume parameters to then quantify the associated river runoff.
This work will provide a rarely obtainable high spatial resolution record especially in Southern and Western Greenland, where numerous rivers drain into fjords. Runoff data will be related to observed melting rates at automated weather stations of the Greenland Climate Network as well as to longer-term temperature and precipitation trends of existing meteorological stations in the fjords to enhance process understanding of runoff dynamics. Lag time between onset and duration of melt on the ice sheet and downstream river discharge patterns contributes to understanding of the presently hotly debated pathways of GrIS melt water to the global ocean. A comprehensive dataset of Greenland river discharge will be useful in better estimating the portioning of observed ice mass lost on the GrIS, between melt water runoff and calving glacier ice discharges. The dataset will be used to evaluate and improve melt and runoff routines for the Community Land Model/Greenland ice sheet model component of the Community Climate System Model by comparing MODIS reconstructions with CCSM output. The reconstructed runoff data has the potential to expose deficiencies in modeled Greenland runoff and will therefore serve as a validation dataset to direct future ice sheet/land model improvements.
