Hotspots of extreme runoff across Arctic land ice

Abstract The Arctic is warming at nearly three times the global average, driving profound shifts in its hydrological cycle. Yet, the impacts of this rapid warming on extreme runoff events—key to ice mass balance, ecosystem dynamics, and global climate feedbacks—remain poorly quantified. Here, we analyze the spatiotemporal evolution of summer extreme runoff across the permanent land ice Arctic area from 1980 to 2020 based on high-resolution regional climate model simulations (MARv3.11). Extreme runoff is defined as summer runoff exceeding the 90th, 95th, or 99th percentile of modeled runoff distributions, consistent with established climate extreme thresholds. We then identify regional hotspots and quantify changes in the fraction of extreme runoff relative to total summer runoff, as well as shifts in its magnitude and drivers. Greenland contributes to most of the land ice Arctic extreme runoff area, accounting for 63% of the total, followed by Baffin (14%) and Ellesmere (8%). Our results reveal a marked intensification of extreme runoff, most notably in the Western Arctic. The fraction of extreme runoff has significantly increased, particularly in Greenland (+46%), Ellesmere (+38%), and Devon (+31%) (1980–2020 vs 2000–2020). In Ellesmere, the spatial extent of extreme runoff has expanded nearly 400%. Overall, the contribution of extreme runoff to total runoff increased by 20%–30% (1980–2020 vs 2000–2020) across the Arctic, with the largest increases in Ellesmere and Devon. A clear West-East gradient is evident, with statistically significant trends in the Western Arctic and more moderate changes in the East. For example, Iceland and Franz Josef Land show only modest increases in the fraction of extreme runoff (+11% and +2%, respectively). These patterns are consistent across multiple thresholds for extreme runoff (90th, 95th, and 99th percentiles) and remain robust after detrending. This intensification of extreme runoff is linked to increases in anticyclonic circulation in the Western Arctic. The results have far-reaching implications, including increased freshwater discharge into the Arctic Ocean and the potential disruption of the Atlantic Meridional Overturning Circulation.