Increasing glacier runoff in northwestern Greenland simulated from 1950 to 2023

Abstract. Increased river runoff due to ice melting in Greenland contributes to sea-level rise, as well as flooding in coastal settlements, posing serious risks to local communities. To investigate fluctuations of glacier runoff in Greenland and its atmospheric drivers, long-term variations in runoff from Qaanaaq Glacier, northwestern Greenland, were reconstructed from 1950 to 2023 using a glacier energy–mass balance model and climate reanalysis dataset. Exceptionally large daily runoff (top 0.1 %) has only happened since 1990, indicative of an increasing frequency of major runoff events in recent decades. The largest (8.7 m³ s⁻¹ in 2023) and second largest (7.2 m³ s⁻¹ in 2001) runoffs resulted in the destruction of roads in the settlement of Qaanaaq, demonstrating the significant effects on the local community. Such large runoffs have been attributed to intense rainfall due to enhanced moisture and heat transport caused by an atmospheric river. Long-term annual glacier runoff is controlled mainly by synoptic-scale atmospheric conditions represented by the Greenland Blocking Index (r = 0.69). Composite analysis of the climate reanalysis dataset suggests particularly high sensitivity of air temperature in northern Greenland to anticyclonic conditions over Greenland, which lead to strengthened warm southerly winds. Accurate representation of such extreme conditions in climate models is crucial for predicting glacier runoff and flood occurrence in Greenland.