Changes in the East Asian summer monsoon rainfall under global warming: moisture budget decompositions and the sources of uncertainty

Abstract

We investigated the changes in the East Asian summer monsoon (EASM) rainfall under global warming based on the historical and representative concentration pathway (RCP) 4.5 runs of 18 models from the fifth phase of the Coupled Model Intercomparison Project (CMIP5). Because the mechanism of rainfall changes under global warming studied in previous studies is widely based on the moisture budget decompositions (MBDs), we first evaluated the applicability of three MBDs for the changes in the EASM rainfall, which are two complete MBDs in Chou et al. (J Clim 22(8):1982–2005; Chou et al., J Clim 22(8):1982–2005, 2009) and Seager et al. (J Clim 23(17):4651–4668; Seager et al., J Clim 23(17):4651–4668, 2010), and the simplified MBD in Huang et al. (Nat Geosci 6(5):357–361; Huang et al., Nat Geosci 6(5):357–361, 2013). The results show that the simplified MBD in Huang et al. (Nat Geosci 6(5):357–361, 2013) is applicable for the EASM rainfall changes, providing an efficient way to study the EASM rainfall changes, which is used in this study. The EASM rainfall changes can be well explained by two components: the thermodynamic component due to the increase in specific humidity and the dynamic component due to the changes in EASM circulation changes. The thermodynamic component is quite robust among the models, whereas the dynamic component with the circulation changes contributes the major uncertainties of the EASM rainfall changes. Moreover, the apparent intermodel difference in the background circulation is another important source of the EASM rainfall changes. The results imply that the background and changes of the EASM circulation are the key factors for further narrowing the uncertainties of the projected EASM rainfall changes.