Eurasian river discharge into the Arctic Ocean has steadily increased during the 20th century, and many studies have documented the spatial distribution of the trends and hypothesized the causes. There is a large variation in the scope of these studies, including the spatial scale of interest, and they often lack consistency in the time period analyzed. Studies have shown a connection between changes in the seasonal snowpack and discharge, but they have been constrained by the limitations of the snow observational network, which contains few long-term stations. This study overcomes these problems by using both in situ observations and a land surface model to evaluate the role snowpack changes have had on increases in runoff across northern Eurasia from 1936 through 1999. Our analysis shows consistent trends in both observations and model predictions. Increases in cold season precipitation propagate into increases in maximum snow water equivalent, which lead to increases in runoff. A series of model experiments demonstrate that the nonlinear interaction between winter precipitation and temperature has driven changes in the snowpack, which are manifested in the modeled runoff trends. Given that winter precipitation is expected to continue to increase and temperatures to warm during the 21st century in this region, these results point to the importance in understanding how the projected changes will influence the seasonal snowpack, which may have important consequences for streamflow in this region and freshwater export to the Arctic Ocean.