Atmospheric Circulation Attribution to Recent Intensification of Arctic Hydrological Cycle

Changes in Arctic freshwater budgets and pathways have important implication for Arctic Ocean circulations and North Atlantic deep convection formation. Studies have shown an intensification of Arctic hydrological cycle in recent decades, which has been outstandingly evidenced by an increase in gauged river discharges from major drainage basins surrounding the Arctic Ocean. The enhanced river discharges could be attributable to the global warming induced increase in precipitation less evaporation, greening change in vegetation coverage and density, and thawing of frozen soil. However, high uncertainties exist in these parameters due to sparse and indirect observations. In this study, we investigated changes in Arctic hydrological cycle from the atmospheric circulation perspective. Relatively, the fundamental atmospheric parameters have been well monitored and these parameters have fewer errors in the global assimilation system output at each assimilation time step. Based on these output at each time step, we developed a correction approach and made the data homogenous physically in a long time period since the middle of 20th century to present. We then examined changes in atmospheric circulation and their contribution to the changes in and variability of the Arctic hydrological cycle. The results show that atmospheric-circulation-driven net moisture transport captures gauged climatological river discharges very well, and plays a predominant forcing role in accelerating Arctic hydrological cycle. In particular, the most-recent spatial shift of atmospheric circulation and the polarization of the newly-identified Arctic Rapid change Pattern (ARP) decisively resulted in the observed record high Eurasian river discharges along with the extreme event of sea ice cover loss in 2007.