Attribution of tropical sea surface temperature change on extreme precipitation over the Yangtze River Valley in 2020

Record-breaking extreme precipitation occurred over the Yangtze River Valley (YRV) in June-July 2020. The impact of climate change on this event is examined from the perspectives of key physical processes including synoptic-scale circulation pattern and tropical sea surface temperature (SST) forcing based on self-organizing map approach and the regularized optimal fingerprinting method. The results indicate that the increase in extreme precipitation over the YRV has accounted for 69% of the increase in total precipitation since 1961. Both the amount and frequency of extreme rainfall during the Meiyu period in 2020 broke the historical record since 1961. The SST warming in tropical Indian Ocean (TIO) and tropical Atlantic Ocean (TAO) lead to the anomalous anticyclone in the Northwest Pacific, which further aggravate the occurrence of extreme precipitation in the YRV. Human influence is the primary cause for the observed SST rise in TIO and TAO since 1961, to which anthropogenic greenhouse gas emissions contribute the most. Quantitatively, the changes of TIO and TAO SST caused by anthropogenic forcing are 0.12 degrees C/10a and 0.08 degrees C/10a, respectively. Such SST warming drives the frequency change of synoptic-scale circulation patterns through air sea interaction. The higher occurrence likelihood of circulation patterns conducive to precipitation in all forcing experiment than that in natural forcing proves that the extreme precipitation in the YRV in 2020 is attributable to human-induced climate change.