Satellite mapping and hydrographic characterization of Greenland-wide proglacial rivers and lakes

Proglacial rivers and lakes act as critical meltwater links between the Greenland Ice Sheet (GrIS) and ocean; however, their spatial distribution and hydrographic characteristics remain unquantified at a large scale. In this study, we extract Greenland-wide proglacial water bodies and propose a new method for classifying them into three types: continuous river networks, isolated lakes, and pathway lakes. First, we combine Sentinel-2 imagery from the summer of 2020 with Copernicus digital elevation model to map proglacial water bodies guided by knowledge of water-landscape interactions. Second, we distinguish continuous river networks from isolated lakes, determine pathway lakes by identifying locations with abrupt width changes and excluding wide braided channels. Third, we analyze the hydrographic characteristics of the proglacial river networks and lakes (e.g. number, area, stream order, width, braiding index, and shape). Fourth, we estimate ice meltwater runoff drained into the ocean via the proglacial river networks using regional climate models. The results show that: (1) our method achieves an average Kappa coefficient of 0.91 ± 0.05 and maps a total area of 14,045.7 km2 of proglacial water bodies across Greenland in the summer of 2020, including 6,630 river networks (2,705.5 km2, accounting for 19.3% of the area), and 88,206 lakes (11,340.2 km2, 80.7%); (2) high-order (order ≥ 4) proglacial river networks account for less than 5% in number but over 60% of the total length, area, and river-routed ice meltwater runoff; (3) meltwater-fed rivers widen faster with the stream order and exhibit higher braiding indices compared to non-meltwater-fed rivers, while pathway lakes are generally larger than isolated lakes, both implying that meltwater exerts strong controls on proglacial hydrography; and (4) proglacial river networks route nearly half (~47%) of the ice meltwater runoff to the ocean in the 2020 summer, approximately to marine-terminating glaciers, while extreme imbalance among major basins is also revealed. Viewing collectively, this study presents a detailed high-resolution hydrography dataset of Greenland proglacial rivers and lakes, attempts to advance from open-water mapping to water type classification, and provides a potential comprehensive dataset for future investigations of Greenland proglacial hydrology and its interactions with the ice sheet and ocean.