Change in spring snowmelt timing in Eurasian Arctic rivers

Changes in the amount and timing of the discharge of major Eurasian Arctic rivers have been well documented, but whether or not these changes can be attributed to climatic factors or to the construction of manmade reservoirs remains unclear. Here we endeavor to identify the key processes (snow cover and air temperature) that have regulated seasonal streamflow fluctuations in the Eurasian Arctic over the last half-century (1958-1999) and to understand the regional coherence of timing trends, using a set of Eurasian Arctic rivers selected specifically because they are free of known effects of dams. We find a shift toward earlier onset of spring runoff as measured by a modest change in the spring pulse onset (26 of 45 stations) and a strong change in the centroid of timing (39 of 45 stations). Winter streamflows increased over the period of record in most rivers, suggesting that trends observed by others in larger regulated Eurasian Arctic rivers may not be entirely attributable to reservoir construction. Upward trends in air temperature appeared to have had the largest impact on spring and summer flows for tributaries in the coldest of the major Eurasian Arctic river basins (e. g., the Lena). While the overall duration of snow cover has not significantly changed across the Eurasian Arctic, snow cover disappearance has trended earlier in the year and appears to be related to the increased May and snowmelt season fractional flows.