Regime Shifts in Arctic Terrestrial Hydrology Manifested From Impacts of Climate Warming

Abstract. Anthropogenic warming in the Arctic is causing hydrological cycle intensification and permafrost thaw, with implications for flows of water, carbon, and energy from terrestrial biomes to coastal zones. To better understand likely impacts of the changes, we used meteorological data from atmospheric reanalysis and two global climate models to drive simulations with a hydrology model that accounts for soil freeze-thaw across the pan-Arctic drainage basin over the period 1980–2100. The simulations point to greater changes over northernmost areas of the basin, areas underlain by permafrost, and the western Arctic. An acceleration of simulated river discharge over the recent past is commensurate with trends drawn from observations and reported in other studies. Annual total runoff increases by 17 and 25 % between early (2000–2019) and late century (2080–2099), while the proportion of subsurface to total runoff is projected to increase 13 and 30 %, with the largest changes noted in summer and autumn, and across areas with permafrost. Most notably, runoff contributions to river discharge shift to northern parts of the Arctic basin that contain higher amounts of soil carbon. In both simulations, each season sees an increase in subsurface runoff, spring is the only season where surface runoff dominates the rise in total runoff, and summer experiences a decline in total runoff, yet an increase in the subsurface component. Greater changes where permafrost exists supports the notion that increased soil thaw is shifting hydrological contributions to more subsurface flow. The manifestations of warming, hydrological cycle intensification, and permafrost thaw will impact Arctic terrestrial and coastal environments through altered river flows and the materials they convey.