Anthropogenic Influence on 2022 Extreme Winter Precipitation over Southern China

From January to February (J–F) 2022, Southern China (SC) experienced abnormally heavy precipitation, with the regionally averaged total precipitation reaching 248 mm, making it the second-largest value since 1961. It was the second highest value since 1961 with the anomaly being about 2.3 standard deviations (2.3ơ, using as the threshold for the 2022 event) above the climatology in the period of 1961-2005. This extreme event resulted in significant damage to transportation, power supply, and crop production. Decreases in precipitation occur in both HadGEM3 and CMIP6 simulations over SC, accompanied by anomalous positive sea level pressure (SLP) and an anomalous anticyclonic circulation over SC.

The two most important anthropogenic forcings are greenhouse gases and atmospheric aerosols and they can have different effects on SC J–F precipitation. Anthropogenic influence reduced the likelihood of extreme events like 2022 by about 50% (55%) in HadGEM3 (CMIP6). Furthermore, the greenhouse gas (GHG) forcing leads to a rightward shift of probability density functions (PDFs) to a wetter climate relative to natural forcing (NAT), while the anthropogenic aerosol (AA) forcing shifts to a drier world. The estimated P_GHG and P_AA indicate that a ~26 years event becomes a ~15 years event with PR_GHG=1.75(1.60–2.00) in GHG and a ~83 years event in AA with PR_AA=0.31 (0.24–0.37).

Analyses of single forcing experiments using CMIP6 model ensembles demonstrate different roles of changes in GHG and AA in J–F precipitation over SC with GHG forcing inducing an increase and AA forcing inducing a decrease. However, the magnitude of AA-induced precipitation decrease is larger than that of GHG-induced increase, leading to the reduced likelihood of the J–F precipitation event similar to that of 2022 in SC by the combined effect of anthropogenic forcing.