Anthropogenic forcing decreases the probability of the 2020 Yangtze River extreme flood and future risk

The Yangtze River basin experienced extreme flooding during the summer of 2020, leading to widespread impact and significant economic losses. However, there is a lack of specific and quantitative anthropogenic attribution analysis. Here, we used the VIC model and the Risk Ratio framework to isolate the contributions of two anthropogenic (ANT) forcings, aka greenhouse gas (GHG) and aerosol (AER), to this event and the associated potential risk. We also assessed future risk by employing projections from four simulations under the SSP2-4.5 scenario in 2041-2100. Our findings reveal that ANT forcing reduces the probability by 74 %, while GHG forcing increase it by 6 %, and AER forcing decreases it by 92 % at the downstream Datong station. At the middle-stream Cuntan station, ANT forcing decreases the probability of extreme floodings similar to the 2020 event by 87 %, while GHG forcing decreases it by 82 %, and AER forcing decreases it by 95 %. In the future period under the SSP2-4.5 scenario, ANT forcing reduces the probability of extreme flood events like 2020 by 78 % and 82 % at the Cuntan and Datong stations, respectively. And The GHG and AER forcings contribute positively and negatively to the probability of flooding in the Yangtze River Basin, respectively, mainly through influencing the probability of extreme precipitation and potential evapotranspiration. Our study provides valuable insights for policymakers to comprehend the anthropogenic influence on extreme flooding and to guide effective risk management strategies. Plain language summary: The Yangtze River basin experienced severe flooding in the summer of 2020, but there is no specific and quantitative anthropogenic attribution analysis yet. Therefore, we performed an attribution analysis using the hydrological model and global climate models to isolate the anthropogenic (ANT) contribution for the 1961-2020 and 2041-2100 periods. We find that ANT forcing decreases the risk of extreme flooding, similar to the 2020 event, at the middle-stream Cuntan station and the downstream Datong station. In the future, ANT forcing significantly reduces the probability of potential extreme flood events in both stations. Additionally, we discovered that the net effect of ANT forcing on extreme flood events is determined by the counterbalance of anthropogenic greenhouse gas and aerosol forcings. Our study aims to help policymakers gain a better understanding of the human impact on extreme flooding and develop effective risk management strategies.