A comparative analysis of the attribution of extreme summer precipitation in south and north parts of the East China monsoon region-with the year 2020 as an example

In summer 2020, several watersheds in China monsoon region experienced historically unusually heavy precipitation. The flooding associated with these heavy precipitation events led to devastating impacts on human life, infrastructure, agriculture and economy. Using historical climate simulations from the HadGEM3-GA6 and CMIP6 models under influences of natural and/or anthropogenic forcings, we conducted a comparative study on the attribution of extremely heavy precipitation events in summer 2020 in the mid-lower reaches of the Yangtze River and the mid-lower reaches of the Yellow River-Hai River Basin which locates respectively in the south and north parts of the East China monsoon region. The potential contributions of anthropogenic forcings to monthly-scale extreme precipitation and daily maximum precipitation (RX1day) were examined. The results suggest that human activities have decreased the probability of month-scale extreme precipitation events in the south part of the East China monsoon region. For RX1day extreme precipitation events, anthropogenic factors have increased their probability in both regions. However, the influence of anthropogenic forcings on month-scale extreme precipitation events in the north part of the East China monsoon region is not robust among the two attribution systems. Further analyses indicated that anthropogenic aerosols (AER) make both month-scale extreme precipitation events and extreme RX1day less likely to occur in summer 2020, and greenhouse gases (GHG) increase the likelihood of both. GHG influences on Rx1day overwhelm AER influences, leading to an increase of the probability of Rx1day similar to the 2020 events in both regions. In contrast, the decrease in the probability of month-scale precipitation in the south part of the East China monsoon region is predominantly due to aerosol forcing. The model projections show that the likelihood of both monthly and daily extreme precipitation events in both regions will increase in the future. Accordingly, the recurrence period of extreme precipitation events will be shortened by the end of the 21st century, which is more significant under the high-emission scenario.