Seasonal evolution of the supraglacial drainage network at Humboldt Glacier, northern Greenland, between 2016 and 2020

Supraglacial rivers and lakes are important for the routing and storage of surface meltwater during the summer melt season across the Greenland Ice Sheet (GrIS) but remain poorly mapped and quantified across the northern part of the ice sheet, which is rapidly losing mass. Here we produce, for the first time, a high-resolution record of the supraglacial drainage network (including both rivers and lakes) and its seasonal behaviour at Humboldt Glacier, a wide-outlet glacier draining a large melt-prone hydrologic catchment (13 488 km 2 ), spanning the period 2016 to 2020 using 10 m spatial resolution Sentinel-2 imagery. Our results reveal a perennially extensive yet interannually variable supraglacial network extending from an elevation of 200 m a.s.l. to a maximum of similar to 1440 m a.s.l. recorded in 2020, with limited development of the network observed in the low-melt years of 2017 and 2018. The supraglacial drainage network is shown to cover an area ranging between 966 km 2 (2018) and 1566 km 2 (2019) at its maximum seasonal extent, with spatial coverage of up to 2685 km 2 recorded during the early phases of the melt season when a slush zone is most prominent. Up-glacier expansion and the development of an efficient supraglacial drainage network as surface runoff increases and the snowline retreats is clearly visible. Preconditioning of the ice surface following a high-melt year is also observed, with an extreme and long-lasting 2019 melt season and over-winter persistence of liquid lakes, followed by low snow accumulation the following spring, culminating in earlier widespread exposure of the supraglacial drainage network in 2020 compared to other years. This preconditioning is predicted to become more common with persistent warmer years into the future. Overall, this study provides evidence of a persistent, yet dynamic, supraglacial drainage network at this prominent northern GrIS outlet glacier and advances our understanding of such hydrologic processes, particularly under ongoing climatic warming and enhanced runoff.