Epoch Difference in the Water Cycle in Siberia: Long-term Variations of the Siberian River Discharge

Abstract:

Among all the rivers flowing into the Arctic Ocean, the three great Siberian rivers; Lena, Yenisei and Ob, are the three largest in terms of water discharge (R), and they are a large source of freshwater. While linear trends of the Rs have been examined in many previous studies, causes of the R variations are still unclear. As pointed out in Fukutomi et al. (2003), during the 1980s to mid-1990s, the observed R of the Lena was negatively correlated with that of the Ob. The precipitation (P) and net precipitation (P-E) also showed negative correlation. These variations were affected by the east-west seesaw pattern of atmospheric circulation and associated moisture transport over Siberia. Our analysis, including records from recent years, revealed that the correlation of the R becomes weak after the mid-1990s, and it was positive during the mid-1950s to 1960s. These results indicated that the relationship between the observed Rs of the Lena and Ob was different in each epoch during the past seven decades. Reconstructed Rs based on the tree-ring during the past two centuries also showed positive and negative correlations in each of the epochs. Interestingly, the correlations were distributed on the negative side. This implies that the east-west seesaw pattern frequently appeared over Siberia. In addition, control simulation with an atmospheric general circulation model (AGCM) suggested that the east-west seesaw pattern appears as an atmospheric internal variability over Siberia. In conclusion, the atmospheric circulation which affects the P variations over Siberia was different in each epoch during the past two centuries, and as a result the relationship between the Rs of the Lena and Ob Rivers were changed in each of the epochs.