Spatial–Temporal Structures of Trend and Oscillatory Variabilities of Precipitation over Northern Eurasia

Combinations of statistical analyses including principal component analysis, and uni- and multivariate singular spectrum analyses, were carried out to characterize the spatial–temporal structures of trend and interannual oscillatory variabilities of precipitation over the major north-flowing river basins in the former Soviet Union. The series of monthly precipitation were corrected for the biases of precipitation measurement due to the gauge-type change and changes in observing procedures. An upward trend was found in the monthly precipitation series for the last half century. This upward trend was stronger in the North Dvina and Pechora River basins, and in the Ob-Irtysh River basins, but much weaker (still upward, though) in the Yenisey–Lena River basins. The notable increases of precipitation over the southwestern part—the Volga and Ural River basins—were found to be due at least in part to the upward phase of some quasi-century periodicity. Generally speaking, the precipitation increases appeared to be more apparent during the cold seasons in the western half of the sector, while in the eastern part, it appeared to be equally or more notable during summer. On the interannual timescales, signals of 4–5-yr and quasi-biennial oscillations were found in the space–time-dependent precipitation series. The 4–5-yr oscillation was quite apparent over the entire Northern Eurasian sector, being stronger over the southeastern and western parts. This oscillation appeared to propagate eastward. The quasi-biennial oscillation was generally weaker; it was very weak during the 1955–65 period. This oscillation was relatively stronger in the western half of the sector and weaker over the eastern half.