On the Impact of Insufficient Atmospheric Moistening on the Low Annual Discharge of Large Rivers in European Russia

The regional peculiarities of annual atmospheric moistening in European Russia are investigated using Standardized Precipitation and Evapotranspiration Index (SPEI). It was found that the proportion of the years with considerable moistening deficiency rose in the drainage basins of the Northern Dvina, Pechora, and Don and dropped in the Volga basin in 1991–2018 vs 1961–1990. The study revealed a close correlation between the discharge of large rivers in European Russia and the annual atmospheric moistening in their basins. Annual low discharge at the Volga and Don was mostly recorded simultaneously with moistening deficiency in their basins either in the same year or for two successive years, while the discharge of northern rivers responded to moistening deficiency in the same year. It is important to highlight the present-day statistically significant increase in the recurrence of the pairs of successive dry years in the Volga basin by a factor of 3.7. Herewith, the deficiency of moistening in its basin in some years drives the increase of the low discharge probability in the next year by a factor of 1.6. The runoff in years with insufficient moistening was shown to be decreased relative to the mean by 4.4% for the Volga, by 8% for the Don, by 8.7% for the Pechora, and by 10.9% for the Northern Dvina.