Interannual variation in summer extreme precipitation over Southwestern China and the possible associated mechanisms

This study explores the spatial-temporal variations in summer extreme precipitation over Southwestern China (SWC). The frequency of summer extreme precipitation (FEP) has exhibited strong interannual variation with slightly strengthened intensity in recent decades. The associated anomalous water vapour transport mainly originates from northern China, the Indian Ocean, the South China Sea and the Northwest Pacific. The high FEP over SWC is generally associated with the strong Eurasian (EU) pattern and the pattern that is similar to Pacific-Japan (PJ) teleconnection. The results further indicate that the anomalous May Arctic sea ice concentration and the sea surface temperature anomaly over the Northwest Pacific play an important role in the variation of FEP over SWC. On the one hand, the reduction in Arctic sea ice concentration intensifies Rossby wave propagation and then stimulates the formation of EU teleconnection pattern. The associated anomalous northeasterly integrated water vapour transport and high-level westerly anomalies can result in strong interannual changes in FEP over SWC. On the other hand, the sea surface temperature anomaly over the Northwest Pacific can induce an anomalous PJ-like pattern, and the associated anomalous southwesterly water vapour transport also exerts an impact on the change in FEP over SWC.