The inter-annual variability of summer precipitation in East Asia is dominated by the East Asian summer monsoon, which is closely associated with the western Pacific subtropical high. Many studies have been performed to investigate the influencing factors of the inter-annual variability of the East Asian summer monsoon and western Pacific subtropical high, which include El Nino-Southern Oscillation (ENSO) and sea surface temperature (SST) anomalies in the tropical Indian Ocean, western tropical Pacific, and central-eastern tropical Pacific. 

The leading empirical orthogonal function (EOF) mode of precipitation represents the dominating pattern of the inter-annual variability of precipitation and could explain a significant portion of its temporal variances, which generally reflects the influence on precipitation in different areas that are exerted by significant climate modulators, such as the ENSO and Arctic Oscillation. Variations of the leading EOF mode of precipitation in East Asia indicate changes of the underlying physical mechanisms related to the climate in East Asia.  

Researchers from the Institute of Atmospheric Physics, Chinese Academy of Sciences revealed that during past decades, the leading mode of summer rainfall in East China has shifted from a previous “？+？” pattern to a recent “+？” pattern. The “？+？” pattern was significant during the period 1962？1991 which was characterized by increased (decreased) rainfall in the Yangtze River valley and decreased (increased) rainfall in South China and North China in the positive (negative) phase years, and the “+？” pattern was significant during the period 2001？2012 which was characterized by increased (decreased) rainfall in areas north of the Yangtze River and decreased (increased) rainfall in areas south of the Yangtze River in the positive (negative) phase years.  

This inter-decadal transition of the leading mode of summer rainfall in East China was further attributed to an inter-decadal change of the influencing mechanism of tropical SSTs on East Asian climate. It is found that the SSTs in the tropical Indian Ocean, western Pacific, and central and eastern Pacific Ocean has all been of below-normal inter-annual variability during the period 2001？2012. The weakened influence from tropical SSTs may lead to a failure of inducing and sustaining a meridional wave-train that features an “anticyclone-cyclone” dipole-structured water vapor transport pattern over East Asia, which is closely associated with the “？+？” leading mode pattern of rainfall, but causes an anticyclonic monopole-structured water vapor transport over East Asia that results in an “+？” leading mode pattern of rainfall.