The Contrast Precipitation Patterns in Yangtze River Valley Between the Two La Niña Decaying Summers in 2021 and 2022

Although the summers of 2021 and 2022 are both in the two successive La Nina decaying stages and under the same climate background of negative Pacific Decadal Oscillation (PDO) phase and global warming trend, they exhibit significantly different and even opposite precipitation patterns in the Yangtze River Valley (YRV) as well as in the Indian monsoon region (IMR). In contrast to the abundant precipitation and lower temperature in the YRV in summer 2021, in summer 2022 the YRV experiences severe drought and extremely high temperatures, which is also accompanied by Mega-floods in the IMR. This study identifies the joint influence of sea surface temperature anomalies (SSTAs) in Nino4 and Barents Sea (BS) regions as the underlying cause for the contrast YRV precipitation anomalies in the summers of 2021 and 2022. Specifically, the cold SSTAs in both Nino4 and BS regions in summer 2021 favor stronger and southward shifted western North Pacific subtropical high (WNPSH), leading to more precipitation in the YRV, which is however generally reversed but more intense in summer 2022 because of the synergistic effect of cold Nino4 and warm BS SSTAs. Moreover, the induced extreme precipitation in the IMR in summer 2022, which is absent in summer 2021 due to the offsetting effect of cold SSTAs in both Nino4 and BS regions, in turn further strengthens the anomalous atmospheric circulations via its released large diabatic heating and serves as a relay pathway for the dramatic drought and heat wave in the YRV. The El Nino-Southern Oscillation (ENSO) is known to be the most significant interannual signal and one of the major factors for summer precipitation anomaly in East Asia. Nevertheless, the two summers of 2021 and 2022 are characterized by almost opposite precipitation patterns in the Yangtze River Valley (YRV) even though they are both in the two successive La Nina decaying stages. Our study demonstrates that except for the cold sea surface temperature anomalies (SSTAs) with obvious differences in both intensity and position in Nino4 region, the opposite SSTAs in Barents Sea region may play a dominant role in determining the strong contrast precipitation patterns in the YRV as well as in the Indian monsoon region (IMR). As the result of the synergistic effect of cold Nino4 and warm BS, the extreme IMR precipitation also serves as a relay pathway for the dramatic drought and heat wave in the YRV in summer 2022. It suggests that to clearly understand and accurately predict the climate anomalies in East Asia should consider the mid-high latitude signals besides the tropical ENSO signal, especially in the context of global warming when the signals and influences from the mid-high latitudes are becoming more and more prominent. The two La Nina decaying summers in 2021 and 2022 see nearly opposite precipitation patterns in Yangtze River valley Synergistic effect of cold Nino4 region and warm Barents Sea is the essential cause for the extreme summer drought in Yangtze River valley Indian monsoon precipitation plays a relaying role in linking the SST forcing and the Yangtze River valley precipitation via teleconnection