Continuing Acceleration of Pan-arctic Hydrology from Updated River Discharge Records

River runoff is an important integrator of hydrological behavior across large regions and it plays a significant role in the fresh-water budget of the Arctic Ocean. Ocean salinity and sea ice formation are critically affected by river input. Significant increase in the fresh water flux to the Arctic Ocean may slow down global ocean circulation by affecting North Atlantic deep water formation. We analyzed variability of the major water balance components across the pan-Arctic drainage basin with a special focus on the river discharge regime. River discharge data up to 2008 for the largest Arctic rivers (Yenisei, Lena, Ob, Severnaya Dvina, Pechora, Kolyma in Eurasia and Mackenzie, Yukon in North America) were used to evaluate long-term flow variability. All of the Eurasian rivers, except Kolyma, showed significant (p<0.05) increasing trends in annual river discharge over 1936-2008. Mean total discharge over 2000-2008 for these six Eurasian rivers was 10 % higher than discharge over 1936-1999. North American rivers also show positive tendency in river discharge over 1965-2008 but the trends are insignificant. Thus the contemporary data further confirms the presence of significant increasing trend in the fresh water discharge to the Arctic Ocean.

To analyze the seasonal trends in river discharge we cannot use river monitoring stations located along many large rivers due to impoundments and other human impacts within the drainage basins. While at first the reservoirs appear small, their impact during low flow (winter period) could be significant even for gauges located very far from reservoir. An analysis of monthly discharge records longer than 50 years for rivers with no significant human impacts has been used to identify seasonal variations and changes in the hydrological regime across the Eurasian pan-Arctic. The results showed significant increase in winter and summer-autumn runoff across many regions of Eurasian pan-Arctic. An integrated analysis of the major components of water balance was made to better understand possible causes of significant runoff changes in the pan-Arctic. The results of the analysis support the conclusion that intensification of hydrological cycle is taking place and, more recently, this acceleration is increasing.