Seasonal evolution of supraglacial lakes in Northeast Greenland

Supraglacial lakes form seasonally on the Greenland Ice Sheet (GIS) during the melt season as surface meltwater accumulates in topographic depressions. These lakes are dynamic, rapidly draining through supraglacial channels or discharging via hydrofractures, contributing to surface runoff and triggering cascading drainage of nearby lakes. Quantifying the spatial and temporal variability of their area, depth and drainage patterns is critical for understanding GIS hydrology and their role in modulating ice sheet behavior. Here we present a quantitative comparison of supraglacial lake evolution and rapid drainage cascade dynamics between contrasting melt years on Northeast Greenland Ice Stream. We analyzed Sentinel-2 observations from the 2019 and 2020 melt seasons using an automated Otsu thresholding approach combining dual water indices such as NDWIice and NDWIGN with topographic depressions from ArcticDEM to map the lakes. Lake depths and volumes were estimated using an empirical relationship between Sentinel-2 reflectance and lake depth calibrated with ICESat-2 ATL03 photon altimetry. We identified rapid drainage events and quantified their spatial and temporal clustering into cascade sequences.

The analysis revealed distinct interannual contrasts in the timing, persistence, and areal extent of supraglacial lakes, reflecting the influence of seasonal temperature variability. In 2019, warmer conditions favored more sustained lake development and prolonged persistence, whereas cooler conditions of 2020 year led to a more rapid rise-and-fall pattern with reduced total storage. Lake formation exhibited a clear elevation dependence, initiating earlier at lower elevations and progressing upward as the melt season advanced. Mid-elevation zones such as  800 to 1000m acted as key reservoirs storing 80% of the total lake volume, hosting the most persistent and voluminous lakes, suggesting their importance in surface-to-bed meltwater routing. Rapid drainage events were different between years despite similar lake inventories. A total of approximately 600 drainage events were identified across both years. Among these approximately 30% of drainage events participated in cascades. Rapid drainage events were concentrated at lower elevations typically below 800m, with a substantial proportion occurring as part of cascading drainage sequences.
Overall, our results demonstrate that variations in melt-season intensity could modulate supraglacial lake persistence, drainage behavior, and cascading dynamics. These findings emphasize the importance of mid-elevation lakes as critical nodes in meltwater transfer and provide new insights into understanding of surface lake water storage and surface-to-bed hydrological connectivity across the NEGIS sector.