Abstract: Surface melt of the Greenland ice sheet and its impact on rising sea levels have become hot topics in international research. Each summer, surface meltwater forms on the Greenland ice sheet, forming supraglacial lakes, supraglacial rivers, and water-filled crevasses. There is a large area of surface meltwater, which exhibits complex structure, and changes rapidly over time. Regional climate models do not accurately simulate the distribution of surface meltwater, and medium resolution satellite images may not reflect spatial and temporal changes in surface meltwater. CubeSats, such as PlanetScope, allow dynamic monitoring of surface meltwater by providing near-daily satellite observation at 3 m spatial resolution. In this study, we extracted surface meltwater in a typical internally drained catchment in the southwest Greenland ice sheet using PlanetScope images. We then constructed a formula to estimate meltwater depth from the PlanetScope images and compared meltwater volume estimated by satellite images and meltwater runoff simulated by the MAR v3.11 model. The results showed that the open water fraction (OWF) of surface meltwater in the catchment first rose then decreased during July and August 2019, peaking on 12 July (8.7%). The surface meltwater depth in the catchment ranged from 0.2 to 1.5 m, and the supraglacial lakes were the deepest (0.9 m±0.2 m), followed by the mainstem of supraglacial rivers (0.6 m±0.1 m), and the tributaries of supraglacial rivers (0.5 m±0.1 m). The OWF, meltwater volume and daily runoff simulated by MAR were positively correlated, indicating that meltwater runoff directly supplies supraglacial lakes and rivers. The surface meltwater storage capacity is limited (<1%), and the catchment is efficiently transporting meltwater into the ice sheet.

Key words: surface meltwater, PlanetScope, remote sensing observation, regional climate model, Greenland ice sheet