Anthropogenic influence on extreme Meiyu rainfall in 2020 and its future risk

Abstract

Eastern China experienced excessive Meiyu rainfall in the summer of 2020, with a long rainy season and frequent extreme rainfall events. Extreme rainfall occurred on daily to monthly time scales. In particular, persistent heavy rainfall events occurred; e.g., the maximum accumulated rainfall over four consecutive weeks (Rx28day) in the lower reaches of the Yangtze River was 94% greater than climatology, breaking the observational record since 1961. With ongoing anthropogenic climate change, it is vital to understand the anthropogenic influence on this extreme rainfall event and its driving mechanisms. In this study, based on multi-model simulations under different external forcings that participate in the Detection and Attribution Model Intercomparison Project (DAMIP) in the Coupled Model Intercomparison Project-phase 6 (CMIP6), we show that anthropogenic forcing has reduced the probability of the Rx28day extreme rainfall as that in observations in the lower reaches of the Yangtze River in 2020, by 46% (22–62%). Specifically, greenhouse gas (GHG) emissions have increased the probability by 44% as a result of atmospheric warming and moistening. However, this effect was offset by anthropogenic aerosols, which reduced the probability by 73% by reducing atmospheric moisture and weakening the East Asian summer monsoon circulation. With the continuous emissions of GHGs and reductions in aerosols in the future, similar persistent heavy rainfall events are projected to occur more frequently. A higher occurrence probability is expected under higher emission scenarios, which is estimated to be 4.6, 13.6 and 27.7 times that in the present day under the SSP1-2.6, SSP2-4.5, and SSP5-8.5 emission scenarios, respectively, by the end of the 21st century. Thus, efficient mitigation measures will help to reduce the impacts related to extreme rainfall.