Interdecadal changes in the western Siberian summer mean and extreme rainfall during 1982–2021

Abstract

Siberia, neighboring the Arctic Ocean, has a cold and dry climate. The famous Siberian forest, Taiga, has been greening in recent decades, mainly driven by climate factors. Besides the warming trend, summer rainfall is also critical for the vegetation variations there. This study finds that summer mean rainfall in western Siberia significantly increases after 1995 and decreases again slightly after 2012. The extreme rainfall shows similar interdecadal variations. Three periods are identified as 1982–1994 (P1), 1995–2011 (P2), and 2012–2021 (P3). The significant anomalous cyclone/anticyclone and water vapor convergence/divergence over western Siberia are responsible for the increased/decreased summer rainfall from P1 to P2/P2 to P3. All the extreme rainfall days show strong cyclonic anomalies in the lower level and a northwest–southeast-oriented anomalous cyclone–anticyclone dipole pattern in the upper level over western Siberia. The above anomalous circulation patterns are strongest during P2, when there are more extreme rainfall days with enhanced intensity. Distinct characteristics also exist in the developing processes of extreme rainfall events in the three periods.摘要本文研究发现, 西西伯利亚夏季降水在1995年后显著增加, 2012年后又有所减少, 极端降水日数和强度呈现一致的变化特征. 伴随这两次降水的年代际增加/减少, 西西伯利亚上空出现异常气旋/反气旋和水汽幅合/幅散. 极端降水发生时的区域环流特征在三个时段基本一致: 西西伯利亚低空出现气旋性异常, 高空为西北–东南向的异常气旋–反气旋偶极子型. 1995–2011年期间, 极端降水日数更多, 强度更强, 上述异常环流型也更强.