Human influence on historical heaviest precipitation events in the Yangtze River Valley

Abstract

With the recurrence of high-impact extreme events and the growing public demands to understand the causes of the events, event attribution has emerged as a frontier of climate change research. Typically, an event attribution study focuses on one individual extreme event that has just occurred. Studies rarely examine human influence on multiple extreme events in different times of the past. Here we conduct a comprehensive attribution analysis on the four heaviest precipitation events in the Yangtze River Valley during the past 100 years. We start by defining extreme precipitation events as the heaviest precipitation over a fixed size area that is of direct relevance to flood preparedness and management. When examining the events over the historical time, we allow the precise location of the area to change in different years. By definition, four extremely strong events are identified, and they happened in the summer of 1931, 1954, 1998 and 2020. We find that the impacts of greenhouse gases (GHGs) and anthropogenic aerosols (AAs) on these events show clear difference in different time period. The impacts were negligible in the early period and became more and more discernible since the late 20th century. The GHGs have gradually increased the occurrence probability of extreme precipitaiton while the AAs have decreased the occurrence of extrem precipitation. These competing effects from the GHGs and AAs have led to a slight and then gradually increasing human influence on extreme precipitation over time. GHGs have exerted a larger influence on short-duration precipitation events while AAs have had a larger influence on monthly mean precipitation. The more extreme the precipitation event, the clearer the anthropogenic influence.