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Changes in precipitation characteristics directly affect society through their impacts on drought and floods, hydro-dams, and urban drainage systems. Global warming increases the water holding capacity of the atmosphere and thus the risk of heavy precipitation. Here, daily precipitation records from over 700 Chinese stations from 1956 to 2005 are analyzed. The results show a significant shift from light to heavy precipitation over eastern China. An optimal fingerprinting analysis of simulations from 11 climate models driven by different combinations of historical anthropogenic (greenhouse gases, aerosols, land use, and ozone) and natural (volcanic and solar) forcings indicates that anthropogenic forcing on climate, including increases in greenhouse gases (GHGs), has had a detectable contribution to the observed shift toward heavy precipitation. Some evidence is found that anthropogenic aerosols (AAs) partially offset the effect of the GHG forcing, resulting in a weaker shift toward heavy precipitation in simulations that include the AA forcing than in simulations with only the GHG forcing. In addition to the thermodynamic mechanism, strengthened water vapor transport from the adjacent oceans and by midlatitude westerlies, resulting mainly from GHG-induced warming, also favors heavy precipitation over eastern China. Further GHG-induced warming is predicted to lead to an increasing shift toward heavy precipitation, leading to increased urban flooding and posing a significant challenge for mega-cities in China in the coming decades. Future reductions in AA emissions resulting from air pollution controls could exacerbate this tendency toward heavier precipitation.

The Community Earth System Model version 1 (CESM1) and version 2 (CESM2)'s abilities to simulate the impacts of Atlantic multidecadal variability (AMV) and Pacific multidecadal variability (PMV) on South American precipitation and temperature have not been assessed, and how the AMV and PMV modulate each other's influences on South American climate is not well understood. Here we use observations, reanalyses, and CESM1 and CESM2 simulations from 1920 to 2015 to study those problems. The models can reproduce the observed precipitation and temperature responses to AMV well, but can only roughly reproduce such responses to PMV. The precipitation response over the South Atlantic convergence zone (SACZ) is better simulated by CESM2 compared to CESM1, which is associated with an improved horizontal moisture flux over this region. However, the models cannot accurately simulate the observed differences between the influences of Pacific interannual and multidecadal variability on South American precipitation and temperature. The impacts of AMV and PMV on South American precipitation are modulated by the other mode via changes in horizontal moisture flux over the SACZ and River Plate basin in summer, as well as changes in vertical motion over the equatorial regions in winter. Similarly, the impacts of AMV and PMV on South American temperature are also modulated by the other mode. Over water‐limited regions, such as northeastern Brazil and southern Argentina, the precipitation and temperature responses are anti‐correlated, possibly via surface evaporation. Plain Language Summary: How the Community Earth System Model version 1 and version 2 simulate the influences of Atlantic and Pacific multidecadal sea surface temperature variations on South American climate has not previously been examined, and how the Atlantic and Pacific multidecadal variability (AMV and PMV) modulates the effects from the other basin on South American precipitation and temperature is unclear. In this study, we analyze historical observations and model simulations during 1920–2015 to investigate those problems. The general patterns of the precipitation and temperature responses to AMV are well simulated by both versions of the model, but the patterns of the responses to PMV are only roughly reproduced by the models. The precipitation response over the South American monsoon region is better represented in the model's version 2 than in version 1. The Atlantic and Pacific variability modulates each other's impacts on South American precipitation and temperature. The variations in the patterns of precipitation response are related to changes in horizontal moisture transport over subtropical regions in summer and vertical motion over equatorial regions in winter. The precipitation and temperature responses are anti‐correlated over relatively dry regions, such as northeastern Brazil and southern Argentina, possibly through surface evaporation. Key Points: The Community Earth System Model version 2 improves monsoon rainfall response to Pacific and Atlantic variability compared to version 1Precipitation anomaly patterns over South America are related to anomalous subtropical moisture flux and equatorial vertical motionOver water‐limited regions, anomalies in temperature and precipitation are anti‐correlated, possibly due to surface evaporative cooling [ABSTRACT FROM AUTHOR]