Abstract
Understanding the physical mechanisms behind the secular trends of summer rainfall extremes over the heavily populated Southeast and East Asian monsoon regions is not only of scientific importance but also of considerable socioeconomic implications. In this study, the relevance of the excessive-rain-producing low pressure systems (LPSs) to extreme rainfall is quantified. Using an objective feature-tracking algorithm, the synoptic-scale LPSs are identified and tracked in the 40-yr ECMWF interim reanalysis. The region experiences approximately 16 terrestrial and 18 marine LPSs each summer. The terrestrial LPSs form near the downwind side of the Tibetan Plateau and travel northeastward toward jet latitudes. The marine LPSs form over the western North Pacific Ocean and migrate along the western periphery of the subtropical high. While both types of LPSs account for a large portion of upper-tail rainfall, the terrestrial LPSs predominantly impact the extreme rainfall over inland areas, and the marine LPSs primarily affect the coastal regions where they frequently make landfall. The historical extreme rainfall trend during 1979–2018 aligns with the changes in LPS tracks. The decreasing number of northeastward-moving terrestrial LPSs leads to an extreme rainfall dipole with negative trends in north-central China and positive trends in southern China, while the increasing number of northward-recurving marine LPSs enhances the extreme rainfall in the eastern China coast but suppresses it over the South China Sea. These trends are driven dynamically by the weakening of the monsoonal southwesterlies and the eastward retreat of the subtropical high, which might be attributable to anthropogenic forcings.
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