Changes in the summer extreme precipitation in the Jianghuai plum rain area and their relationship with the intensity anomalies of the south Asian high

Abstract Based on the daily precipitation data of 66 stations in the Jianghuai plum rain area from 1960 to 2014 and the concurrent reanalysis data of NCEP/NCAR, this study utilized several techniques, including trend analysis, empirical orthogonal function (EOF) analysis and composite analysis, to investigate the spatio-temporal changes of the summer extreme precipitation in the area and their relationship with the intensity anomalies of the south Asian high (SAH). The main results are as follows: (1) The first eigenvector of the summer extreme precipitation indices (EPIs) PQ90 and PNL90 exhibits a distribution pattern of uniform “+”, and the first principal component (PC1) shows a significant increasing trend. The second eigenvector generally exhibits a dipole pattern of “south +, north –”, and the second principal component (PC2) of PQ90 shows a significant increasing trend. (2) The intensity index of the summer SAH (SAHI) underwent an abrupt change around 1977, with a subsequent increasing trend. The SAHI depicts a significant positive correlation with PC1 of PNL90 and PQ90, thus the EPIs are higher during the years with a strong SAH. (3) When the SAH shifts eastward (westward) and strengthens (weakens) and the location of the western Pacific subtropical high shifts westward (eastward), the mid-latitude region displays the characteristics of a meridional (zonal) circulation pattern, facilitating (hindering) the occurrence of extreme precipitation in the Jianghuai plum rain area. In addition, corresponding to the above-mentioned circulation patterns, vertical movement over the Jianghuai plum rain area strengthens (weakens), and thus water vapor fluxes enhance and converge (weaken and diverge). Therefore, extreme precipitation in the study area strengthened (weakened). (4) The preceding changes in the atmospheric heat source over the eastern Qinghai-Tibet Plateau (one month in advance) affects the changes of the intensity of the following SAH significantly. The changes in the vertically integrated apparent heat sources 〈Q1〉over the eastern Qinghai-Tibet Plateau and the sea surface to the east of the Philippines and the apparent moisture sink of the Jianghuai plum rain area is an important factor for the above-mentioned adjustment in the circulation structure and changes in extreme precipitation.