Since the mid-1990s precipitation trends over eastern China display a dipole pattern, characterized by positive anomalies in the south and negative anomalies in the north, named as the Southern-Flood-Northern-Drought (SFND) pattern. This work investigates the drivers of decadal changes of the East Asian summer monsoon (EASM), and the dynamical mechanisms involved, by using a coupled climate model (specifically an atmospheric general circulation model coupled to an ocean mixed layer model) forced by changes in (1) anthropogenic greenhouse gases (GHG), (2) anthropogenic aerosol (AA) and (3) the combined effects of both GHG and AA (All Forcing) between two periods across the mid-1990s. The model experiment forced by changes in All Forcing shows a dipole pattern of response in precipitation over China that is similar to the observed SFND pattern across the mid-1990s, which suggests that anthropogenic forcing changes played an important role in the observed decadal changes. Furthermore, the experiments with separate forcings indicate that GHG and AA forcing dominate different parts of the SFND pattern. In particular, changes in GHG increase precipitation over southern China, whilst changes in AA dominate in the drought conditions over northern China. Increases in GHG cause increased moisture transport convergence over eastern China, which leads to increased precipitation. The AA forcing changes weaken the EASM, which lead to divergent wind anomalies over northern China and reduced precipitation.


  • Summer precipitation over East Asia is mainly associated with the East Asian summer monsoon (EASM)

  • Corresponding to changes in precipitation is the weakened EASM, characterized by positive sea level pressure (SLP) anomalies over Asian continent and India, weaker southeasterly flow from the Indian Ocean and less moisture transport to northern China

  • We have performed a set of time-slice experiments using MetUM-GOML1 to quantify the roles of changes in: (1) All Forcing, the combined effects of greenhouse gas (GHG) and anthropogenic aerosols (AA) emissions, (2) GHG forcing and (3) AA emissions in generating the observed SFND pattern

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Summer precipitation over East Asia is mainly associated with the East Asian summer monsoon (EASM). Associated with the weakened EASM circulation is enhanced precipitation over the middle and lower reaches of the Yangtze River valley and over south China, and suppressed precipitation over northern China. This pattern of rainfall change is named the “Southern Flood Northern Drought” (SFND) pattern (i.e. Wang 2001; Ding et al 2008, 2009, note the time-period used to define the SFND in this study is different due to the need to avoid volcanic eruptions). Based on the coupled general circulation model (CGCM) Bergen Climate Model (BGM), and by using multi-ensemble simulations, Wang et al (2013) argued that the SFND pattern is predominantly forced by the combined effect of increasing GHG and aerosol emissions


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