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Numerous circulation indices have been applied in practical climate services focused on regional precipitation. It is beneficial to identify the most influential or decisive indices, but this is difficult with conventional correlation analyses because of the underlying nonlinear mechanisms for precipitation. This paper demonstrates a set of the most influential indices for July–August precipitation in North China, based on the recursive random forest (RRF) method. These decisive circulation indices include the Polar–Eurasia teleconnection, North African subtropical high ridge position, India–Burma trough, Antarctic Oscillation, Northern Hemisphere polar vortex central latitude, North Atlantic Oscillation, and western Pacific subtropical high northern boundary position. Some of these factors have been recognized as directly influential to the regional precipitation, for example, those of the northwestern Pacific subtropical high; however, some are not easily understood. Decision tree (DT) models using these indices were developed to facilitate composite analyses to explain the RRF results. Taking one of the most interesting DT rules as an example, when the North African subtropical high ridge position is sufficiently far south, an anomalous anticyclone occurs in the upstream and an anomalous cyclone in the downstream of North China. This is unfavorable for northward moisture transport in eastern China and hence causes less precipitation in North China than climatology. The present results are not only helpful for improving diagnostic models of regional precipitation, but also enlightening for exploring how global climate change could impact a region by modulating large-scale circulation patterns. [ABSTRACT FROM AUTHOR]

This study documents the decadal changes of the summer precipitation in East China, with increased rainfall in the Huang-Huai River region (HR) and decreased in the Yangtze River region (YR) during 2000-2008 in comparison to 1979-1999. The main features of the atmospheric circulation related to the increased precipitation in the HR are the strengthened ascending motion and slightly increased air humidity, which is partly due to the weakened moisture transport out of the HR to the western tropical Pacific (associated with the weakened westerly over East Asia and the warming center over the Lake Baikal). The rainfall decrease in the YR is related to the weakened ascending motion and reduced water vapor content, which is mainly related to the weakened southwesterly moisture flux into the YR (associated with the eastward recession of the Western Pacific Subtropical High). The global sea surface temperature (SST) also shows significant changes during 2000-2008 relative to 1979-1999. The shift of the Pacific decadal oscillation (PDO) to a negative phase probably induces the warming over the Lake Baikal and the weakened westerly jet through the air-sea interaction in the Pacific, and thus changes the summer precipitation pattern in East China. Numerical experiments using an atmospheric general circulation model, with prescribed all-Pacific SST anomalies of 2000-2008 relative to 1979-1999, also lend support to the PDO's contribution to the warming over the Lake Baikal and the weakened westerlies over East China. [ABSTRACT FROM AUTHOR]