11:00 〜 13:00
[ACG43-P11] Multidecadal variability in summer precipitation over three large river basins in Siberia
キーワード：数十年規模変動、夏季降水量、大西洋数十年規模振動、太平洋十年規模振動、北東ユーラシア
Summer precipitation variability over Siberia significantly impacts the changes in river discharge into the Arctic Ocean from the three major Siberian river basins (Ob, Yenisei, and Lena). In Siberia, summer precipitation is derived mainly from evapotranspiration from the land surface, whereas large-scale moisture flux convergence is relatively small. The boreal forest plays an essential role in the hydroclimate of Siberia. On the other hand, it has been reported that boreal forests in eastern Siberia were severely damaged by permafrost degradation and waterlogging owing to the abnormal summer precipitation from 2005 to 2008. Therefore, revealing the spatiotemporal variability of Siberian summer precipitation is essential for understanding the hydrological cycle and forest ecosystem in high-latitude regions of the Northern Hemisphere. Multidecadal variability of the summer precipitation over Siberia has not been well understood. The relationship between the changes in the hydrological cycle driven by such variability and that associated with global climate warming remains unclear. This study investigates multidecadal variability in summer precipitation over three major Siberian river basins. We also identified large-scale atmospheric circulation anomalies related to the summer precipitation variabilities.
The dominant temporal variations of summer precipitation in the three major Siberian basins were frequently detected using time series precipitation data of CRU (Climatic Research Unit gridded Time Series v4.05) from 1901–2020 (120 years). The 5–10-yr cycle variability was pronounced in the Ob and Lena river basins. In the Ob River basin, multidecadal (20–40-yr) summer precipitation was dominant during the 1950s–1970s. On the other hand, the 20–40-yr cycle was dominant in the Lena River basin since the 1970s. On the contrary, significant other multidecadal (45–90-yr) variability was dominant only in the Yenisei River basin throughout 1901–2020. The spatial distribution of the predominant 20–40-yr cycle of summer precipitation indicates a north-south seesaw pattern with opposite phases in the Ob and Lena River basins. The spatial distribution of summer precipitation anomalies associated with the 45–90 years cycle is predominant over a wide area extending from the Ob to the Lena River basin, especially in the lower reaches of the Yenisei River basin.
We investigated the relationship between the 20–40-yr cycle of summer precipitation in the Lena River basin and the atmospheric circulation pattern over the Eurasian continent using the JRA55 (Japanese 55-year Reanalysis) data from 1958–2020. A stationary wave train pattern along with a sub-polar jet (65–75N°) was identified from the North Atlantic to the North Pacific (across the Eurasian continent) with the 20–40-yr cycle. The stationary wave pattern corresponding to the 20-40-yr precipitation cycle is similar to the regressed circulation pattern associated with the summer PDO (Pacific Decadal Oscillation) index. In particular, a positive precipitation year in the Lena River basin associated with the 20–40-yr variation corresponds to a negative phase of the PDO, and statistically significant anticyclonic anomalies were observed over the Sea of Okhotsk. The difference in spatial distribution between high (low) precipitation years associated with the 20–40-yr cycle before and after the 2000s in the Lena River basin was influenced by the 45–90-yr cycle associated with the AMO (Atlantic Multidecadal Oscillation). The results suggest that the phase of the AMO modulated the 20-40-yr cycle of summer precipitation in the Lena River basin.
The dominant temporal variations of summer precipitation in the three major Siberian basins were frequently detected using time series precipitation data of CRU (Climatic Research Unit gridded Time Series v4.05) from 1901–2020 (120 years). The 5–10-yr cycle variability was pronounced in the Ob and Lena river basins. In the Ob River basin, multidecadal (20–40-yr) summer precipitation was dominant during the 1950s–1970s. On the other hand, the 20–40-yr cycle was dominant in the Lena River basin since the 1970s. On the contrary, significant other multidecadal (45–90-yr) variability was dominant only in the Yenisei River basin throughout 1901–2020. The spatial distribution of the predominant 20–40-yr cycle of summer precipitation indicates a north-south seesaw pattern with opposite phases in the Ob and Lena River basins. The spatial distribution of summer precipitation anomalies associated with the 45–90 years cycle is predominant over a wide area extending from the Ob to the Lena River basin, especially in the lower reaches of the Yenisei River basin.
We investigated the relationship between the 20–40-yr cycle of summer precipitation in the Lena River basin and the atmospheric circulation pattern over the Eurasian continent using the JRA55 (Japanese 55-year Reanalysis) data from 1958–2020. A stationary wave train pattern along with a sub-polar jet (65–75N°) was identified from the North Atlantic to the North Pacific (across the Eurasian continent) with the 20–40-yr cycle. The stationary wave pattern corresponding to the 20-40-yr precipitation cycle is similar to the regressed circulation pattern associated with the summer PDO (Pacific Decadal Oscillation) index. In particular, a positive precipitation year in the Lena River basin associated with the 20–40-yr variation corresponds to a negative phase of the PDO, and statistically significant anticyclonic anomalies were observed over the Sea of Okhotsk. The difference in spatial distribution between high (low) precipitation years associated with the 20–40-yr cycle before and after the 2000s in the Lena River basin was influenced by the 45–90-yr cycle associated with the AMO (Atlantic Multidecadal Oscillation). The results suggest that the phase of the AMO modulated the 20-40-yr cycle of summer precipitation in the Lena River basin.