Trend and interannual variation in summer precipitation in eastern Siberia in recent decades

ABSTRACT We analysed the long‐term trend and interannual variability in summer (JJA) precipitation over eastern Siberia (90°–140°E, 50°–70°N) for the period 1979–2007. An increasing trend in summer precipitation was observed over large areas (Yenisei and Lena river basins) of eastern Siberia. Summer mean 850‐hPa geopotential height decreased from Siberia to the marginal seas north of Siberia, with the largest decreases occurring over the northern part of eastern Siberia, while increasing trends were found around Mongolia, inducing a significant increase in westerly moisture flux and its convergence over eastern Siberia. Empirical orthogonal function (EOF) analysis of detrended summer precipitation revealed the leading modes of the interannual variability. The first leading mode (EOF1) represents interannual variation around the central Siberian Plateau and the middle reaches of the Lena river basin, related to the enhancement of a low‐level cyclonic circulation centred on 65°N, 100°E around eastern Siberia. The circulation pattern of EOF1 closely matches the trend pattern over Siberia, indicating that a deeper quasi‐stationary trough appears with increasing frequency in recent decades. The second leading mode (EOF2) shows a dipole pattern between the middle reaches of the Lena river basin and the western part of the Central Siberian Plateau. Wet summers in the Lena river basin are related to a stationary trough centred at around 60°N, 130°E. These leading patterns are related to the change in position of the stationary trough and the ridge of the wave train structure along the Arctic polar jet across the northern Eurasian continent.